Article: 97758 of rec.radio.amateur.homebrew From: jasen Subject: Re: FA KEITHLEY 610C ELECTROMETER, PICO AMMETER COULOMB METER Plus References: <8659g.23076$mX1.20976@newsfe2-gui.ntli.net> Message-ID: <66da.449fa326.573d6@clunker.homenet> Date: Mon, 26 Jun 2006 09:04:38 -0000 On 2006-06-25, ctyguy wrote: > Who pray tell, would have the need to measure coulombs? A "coulomb" is an > abstract number of electrons assigned to current 'flow'." someone who's dealing with static electricity. -- Bye. Jasen Article: 97760 of rec.radio.amateur.homebrew From: john wilkinson Subject: Spurs on mixer output Date: Tue, 27 Jun 2006 21:37:44 +0100 Message-ID: Hi, If I feed my second mixer into a spectrum analyser, and inject a 44.545MHz LO, with no power to the first IF stage, I see spurs at about 48-50KHz intervals on the mixer output, from 0 to the 455KHz normal output freq. The mixer is an SBL-1. Any ideas as to where these are comming from? Best regards, John Article: 97761 of rec.radio.amateur.homebrew From: nospam@nouce.bellatlantic.net Subject: Re: Spurs on mixer output Message-ID: References: Date: Tue, 27 Jun 2006 17:03:06 GMT On Tue, 27 Jun 2006 21:37:44 +0100, john wilkinson wrote: >Hi, >If I feed my second mixer into a spectrum analyser, and inject a 44.545MHz >LO, with no power to the first IF stage, I see spurs at about 48-50KHz >intervals on the mixer output, from 0 to the 455KHz normal output freq. > >The mixer is an SBL-1. > >Any ideas as to where these are comming from? > >Best regards, >John You have spurs on one or both of the inputs to the SBL1. Passive doide mixers will not generate spurs like that though they may pass them through if the sources are dirty. Also the IF could also be oscillating and your see ing that contribution. If its the 100db IF duscussed before, thats a lot of gain and I'd hope its bypassed and shielded very well. Allison Article: 97762 of rec.radio.amateur.homebrew From: john wilkinson Subject: Re: Spurs on mixer output Date: Wed, 28 Jun 2006 19:48:20 +0100 Message-ID: References: On Tue, 27 Jun 2006 17:03:06 +0000, nospam wrote: > On Tue, 27 Jun 2006 21:37:44 +0100, john wilkinson > wrote: > >>Hi, >>If I feed my second mixer into a spectrum analyser, and inject a 44.545MHz >>LO, with no power to the first IF stage, I see spurs at about 48-50KHz >>intervals on the mixer output, from 0 to the 455KHz normal output freq. >> >>The mixer is an SBL-1. >> >>Any ideas as to where these are comming from? >> >>Best regards, >>John > > You have spurs on one or both of the inputs to the SBL1. Passive > doide mixers will not generate spurs like that though they may pass > them through if the sources are dirty. > > Also the IF could also be oscillating and your see ing that > contribution. If its the 100db IF duscussed before, thats a lot of > gain and I'd hope its bypassed and shielded very well. > > Allison Hi Allison, I have disconected the second mixer from the output of the first IF amp. That amp is powered down, and disconnected from any supply. The LO input to the mixer is from a crystal oscillator, at 7-8dBm. The output from the mixer is into the spectrum analyser only, not the second IF. This morning I did an experiment. If I left the RF port unterminated, the output was quite clean on the analyser. If I put a 50 Ohm term to gnd, the spurs appear. Maybe it is on the LO itself, but looking at the LO on the analyser it looks OK to me. Thanks, John Article: 97763 of rec.radio.amateur.homebrew From: john wilkinson Subject: A sudden thought Date: Wed, 28 Jun 2006 22:10:46 +0100 Message-ID: Thank you all for being pacient with me and my stupid questions. Another thought has just raised its head. I have 2 IF amps. 1ts with approx 20dB gain, second with 100dB gain. The first IF has a XTAL filter at 45MHz. The second has the collins mech filter at the beginnig, then 100dB gain, straight into a diode detector. I think I need some form of additional filtering at the output of the second IF, before the detector, to reduce the noise introduced by the 100dB amp, else it don't work. Except for strong signals. Is that right? Many thanks, John. Article: 97764 of rec.radio.amateur.homebrew From: nospam@nouce.bellatlantic.net Subject: Re: Spurs on mixer output Message-ID: References: Date: Wed, 28 Jun 2006 00:50:03 GMT On Wed, 28 Jun 2006 19:48:20 +0100, john wilkinson wrote: >> You have spurs on one or both of the inputs to the SBL1. Passive >> doide mixers will not generate spurs like that though they may pass >> them through if the sources are dirty. >> >> Also the IF could also be oscillating and your see ing that >> contribution. If its the 100db IF duscussed before, thats a lot of >> gain and I'd hope its bypassed and shielded very well. >> >> Allison >Hi Allison, > >I have disconected the second mixer from the output of the first IF amp. >That amp is powered down, and disconnected from any supply. >The LO input to the mixer is from a crystal oscillator, at 7-8dBm. >The output from the mixer is into the spectrum analyser only, not the >second IF. > >This morning I did an experiment. If I left the RF port unterminated, the >output was quite clean on the analyser. >If I put a 50 Ohm term to gnd, the spurs appear. Either the LO is dirty and your not seeing it due to overdriving the analyser or the stages after SBL1 are dirty. What I'd expect with the input of the SBL1 terminated and the LO applied is the LO (40db or so down) some second and third harmonic also way down and if you go far enough down some noise. >Maybe it is on the LO itself, but looking at the LO on the analyser it >looks OK to me. Ok whats at the output of the SBL1? Or more specifically whats between the SBL1 and the Analyser? Allison Article: 97765 of rec.radio.amateur.homebrew From: nospam@nouce.bellatlantic.net Subject: Re: A sudden thought Message-ID: References: Date: Wed, 28 Jun 2006 00:59:42 GMT On Wed, 28 Jun 2006 22:10:46 +0100, john wilkinson wrote: >Thank you all for being pacient with me and my stupid questions. > >Another thought has just raised its head. > >I have 2 IF amps. 1ts with approx 20dB gain, second with 100dB gain. >The first IF has a XTAL filter at 45MHz. >The second has the collins mech filter at the beginnig, then 100dB gain, >straight into a diode detector. > >I think I need some form of additional filtering at the output of the >second IF, before the detector, to reduce the noise introduced by the >100dB amp, else it don't work. Except for strong signals. is this FM or AM/SSB/CW? IF FM the 100db amp will be limiting by time the input is around 10uV. IF AM/SSB/CW you should be seeing AGC voltage developed by time the input is 10uV (50 at the extreme max). I suspect the 20db 1st IF is not happy. FYI those 45mhz filters are fairly wide (usualy 15khz or more). So any selectivity is developed in the latter stages (your MF). However the problem is you can easily be overloaded by strong close signals by then. >Is that right? Depends on the answer to the question. >Many thanks, >John. Allison Article: 97766 of rec.radio.amateur.homebrew From: tim gorman Subject: Re: Spurs on mixer output References: Message-ID: <9c0u7e.qnd.ln@tg6124.ab0wr.net> Date: Wed, 28 Jun 2006 07:43:20 -0500 john wilkinson wrote: > > > Hi, > If I feed my second mixer into a spectrum analyser, and inject a 44.545MHz > LO, with no power to the first IF stage, I see spurs at about 48-50KHz > intervals on the mixer output, from 0 to the 455KHz normal output freq. > > The mixer is an SBL-1. > > Any ideas as to where these are comming from? > > Best regards, > John A couple of observations. If you simply disconnected the second mixer from the 1st mixer then it sounds like you do not have the output of the 1st mixer properly terminated. Unless, that is, the spectrum analyzer provides a good 50ohm termination in the probe. The SBL-1 is a double-balanced mixer but in order to get the "balance" to work right you must properly terminate *all* ports. Otherwise all kinds of impedances can be "thrown" back to the other ports - causing all kinds of problems with attached LO's and RF stages. Regularly spaced spurs from DC to 455khz does not sound like spurious mixing products. It sounds more like an oscillator being driven into saturation causing square waves to be produced which are providing regular harmonic outputs. This could be a product of poor terminations on the mixer ports. Directly connecting the output of a SBL-1 to the input of another mixer, even another SBL-1, is not recommended either. The SBL-1 does not have built-in terminations. A good, symmetric, 50ohm 3db pad between the stages would provide a much better setup and would not significantly impact your overall noise factor. Be sure and connect your spectrum analyzer to the far side of the pad. tim ab0wr Article: 97767 of rec.radio.amateur.homebrew From: Markus Wolfgart Subject: Identification of rare/obsolete parts Date: Wed, 28 Jun 2006 15:41:36 +0200 Message-ID: <4gff8hF1nh7k7U1@news.dfncis.de> Dear Friends, I had currently buy some semiconducors at the ham radio exhibition in Germany but there are some parts that are unknown to me. Could you help me to solve that miracle or point me to a link where to find some information on these parts. Many thanks in advance for your help. Markus DL8MBY imprint Manf. Case additional imprint 21H9983 ST QFP48 uC J920A009 controller ?? 50H7012 IBM QFP48 1414PQ no ide CTS9415 ??? SO16 passive part like r-chain ?? OATI A1A ??? SO8 no idea (opv) PE-65101-001 Puls Eng. DIL WB 16 DC/DC Converter ?? IOR017G IR??? SMD (TO220) Power FET ?? M993Q0126D ST DIL16 62P00C/RFA Memory ?? 32H9511 ??? ??? 75.000 KA 0050 XCO ?? Article: 97768 of rec.radio.amateur.homebrew From: Markus Wolfgart Subject: Re: Identification of rare/obsolete parts Date: Wed, 28 Jun 2006 17:00:00 +0200 Message-ID: <4gfjrhF1mk64tU1@news.dfncis.de> References: <4gff8hF1nh7k7U1@news.dfncis.de> <1151505602.458515.214910@75g2000cwc.googlegroups.com> Hi Tim, thanks for prompt reply. In this case as it could be a passive device, I will try to find the pinout by a ohm meter. Bye Markus Tim Shoppa schrieb: > Markus Wolfgart wrote: >> PE-65101-001 Puls Eng. DIL WB 16 DC/DC Converter ?? > > This maker (and others) do broadband transformers in DIL packages. > > Some of these (especially those used in twisted pair/Ethernet) very > commonly show up on the surplus market. > > It would be interesting to repurpose them for ham use (e.g. the 88mH > toroids from the NA Bell system in the mid-20th century.) > > Tim. > Article: 97769 of rec.radio.amateur.homebrew From: john wilkinson Subject: Re: A sudden thought Date: Thu, 29 Jun 2006 19:09:31 +0100 Message-ID: References: On Wed, 28 Jun 2006 22:10:46 +0100, john wilkinson wrote: > Thank you all for being pacient with me and my stupid questions. > > Another thought has just raised its head. > > I have 2 IF amps. 1ts with approx 20dB gain, second with 100dB gain. > The first IF has a XTAL filter at 45MHz. > The second has the collins mech filter at the beginnig, then 100dB gain, > straight into a diode detector. > > I think I need some form of additional filtering at the output of the > second IF, before the detector, to reduce the noise introduced by the > 100dB amp, else it don't work. Except for strong signals. > > Is that right? > > Many thanks, > John. I put a ceramic filter after my last AD603 amp, and bingo!!! I get quite good reception. I think the 2 off AD603 with no output filtering was swamping the diode detector with the noise floor level. However, the detector is buffered from the filter through an emitter follower, and guess what it oscillates at 170MHz. How do I cure this? Has anyone seen an emitter follower oscillating before? Article: 97770 of rec.radio.amateur.homebrew From: john wilkinson Subject: Filter type Date: Thu, 29 Jun 2006 19:17:53 +0100 Message-ID: Hi, When I was looking at an IF amp in the "Experimental mathods in RF", I noticed a filter I have not seen before. I will try to describe: 200 Ohm i/p impedance feeding 1 cap. The othe side of the cap feeds another cap down to ground and an inductor. The other side of the inductor has a cap down to ground. The junction of the ind and cap, has another cap feeding a load of 100 Ohm. When I simulate this it is a bandpass filter. What do you call this filter, and where can I find some info about it? Thanks, John Article: 97771 of rec.radio.amateur.homebrew From: nospam@nouce.bellatlantic.net Subject: Re: Spurs on mixer output Message-ID: References: <9c0u7e.qnd.ln@tg6124.ab0wr.net> Date: Wed, 28 Jun 2006 20:12:21 GMT On Wed, 28 Jun 2006 07:43:20 -0500, tim gorman wrote: >john wilkinson wrote: > >> >> >> Hi, >> If I feed my second mixer into a spectrum analyser, and inject a 44.545MHz >> LO, with no power to the first IF stage, I see spurs at about 48-50KHz >> intervals on the mixer output, from 0 to the 455KHz normal output freq. > >> The mixer is an SBL-1. >> >> Any ideas as to where these are comming from? >> >> Best regards, >> John > >A couple of observations. > >If you simply disconnected the second mixer from the 1st mixer then it >sounds like you do not have the output of the 1st mixer properly >terminated. Unless, that is, the spectrum analyzer provides a good 50ohm >termination in the probe. The SBL-1 is a double-balanced mixer but in order >to get the "balance" to work right you must properly terminate *all* ports. >Otherwise all kinds of impedances can be "thrown" back to the other ports - >causing all kinds of problems with attached LO's and RF stages. > >Regularly spaced spurs from DC to 455khz does not sound like spurious mixing >products. It sounds more like an oscillator being driven into saturation >causing square waves to be produced which are providing regular harmonic >outputs. This could be a product of poor terminations on the mixer ports. Tim, the LO is 45.455 (or 44.545) either way there should be no LF outputs from the mixer below the LO injection unless it's a spur on the LO. >Directly connecting the output of a SBL-1 to the input of another mixer, >even another SBL-1, is not recommended either. The SBL-1 does not have >built-in terminations. A good, symmetric, 50ohm 3db pad between the stages >would provide a much better setup and would not significantly impact your >overall noise factor. Be sure and connect your spectrum analyzer to the far >side of the pad. Thats true though his testing is with a 20db IF after it and one would hope that does present a 50ohm match to the IF port. Usually if the poarts are badly matched the mixing spurs are greater and the port to port isolation go to pot. If the only thing going in is the LO then likely the LO is the source but if there is gain flollowing then the gain stage is also suspect. I've worked with enough SBL1 and MD108s and all their similar DBMS to know the SBL1 in this case is not the offendor Even if misterminated. Likely causes are the 45mhz filter is looking reactive to the IF amp and the IF is unstable (makes a fine OSC) or there is some other source of RF that is unaccounted for (spurs). Allison Kb!GMX Article: 97772 of rec.radio.amateur.homebrew From: nospam@nouce.bellatlantic.net Subject: Re: A sudden thought Message-ID: <8so5a29n9grh749ja473j9sjqfhm93g35q@4ax.com> References: Date: Wed, 28 Jun 2006 20:17:51 GMT On Thu, 29 Jun 2006 19:09:31 +0100, john wilkinson wrote: >On Wed, 28 Jun 2006 22:10:46 +0100, john wilkinson wrote: > >> Thank you all for being pacient with me and my stupid questions. >> >> Another thought has just raised its head. >> >> I have 2 IF amps. 1ts with approx 20dB gain, second with 100dB gain. >> The first IF has a XTAL filter at 45MHz. >> The second has the collins mech filter at the beginnig, then 100dB gain, >> straight into a diode detector. >> >> I think I need some form of additional filtering at the output of the >> second IF, before the detector, to reduce the noise introduced by the >> 100dB amp, else it don't work. Except for strong signals. >> >> Is that right? >> >> Many thanks, >> John. >I put a ceramic filter after my last AD603 amp, and bingo!!! I get quite >good reception. > >I think the 2 off AD603 with no output filtering was swamping the diode >detector with the noise floor level. Maybe or the filter is stripping off out of band oscillations. >However, the detector is buffered from the filter through an emitter >follower, and guess what it oscillates at 170MHz. > >How do I cure this? > >Has anyone seen an emitter follower oscillating before? > Try 33ohm in the base lead. IF an emitter follower is oscilating I'd syspect layout has it looking like a VHF colpits osc. Any layout will oscilate if the effective gains is >1. Allison Article: 97773 of rec.radio.amateur.homebrew From: nospam@nouce.bellatlantic.net Subject: Re: Filter type Message-ID: References: Date: Wed, 28 Jun 2006 20:27:15 GMT On Thu, 29 Jun 2006 19:17:53 +0100, john wilkinson wrote: >Hi, >When I was looking at an IF amp in the "Experimental mathods in RF", I >noticed a filter I have not seen before. >I will try to describe: Cite page and figure for faster finding. Its a thick book. I'd think it's described in the book. > >200 Ohm i/p impedance feeding 1 cap. The othe side of the cap feeds >another cap down to ground and an inductor. The other side of the inductor >has a cap down to ground. The junction of the ind and cap, has another cap >feeding a load of 100 Ohm. > >When I simulate this it is a bandpass filter. Likely it's a simple capacitively tapped tuned circuit. >What do you call this filter, and where can I find some info about it? > >Thanks, >John Allison Article: 97774 of rec.radio.amateur.homebrew From: "W3JDR" References: Subject: Re: Filter type Message-ID: Date: Wed, 28 Jun 2006 22:27:05 GMT Values???; frequency??? "john wilkinson" wrote in message news:pan.2006.06.29.18.17.52.418843@clara.co.uk... > Hi, > When I was looking at an IF amp in the "Experimental mathods in RF", I > noticed a filter I have not seen before. > I will try to describe: > > 200 Ohm i/p impedance feeding 1 cap. The othe side of the cap feeds > another cap down to ground and an inductor. The other side of the inductor > has a cap down to ground. The junction of the ind and cap, has another cap > feeding a load of 100 Ohm. > > When I simulate this it is a bandpass filter. > > What do you call this filter, and where can I find some info about it? > > Thanks, > John Article: 97775 of rec.radio.amateur.homebrew From: "Ken Ward" References: <8659g.23076$mX1.20976@newsfe2-gui.ntli.net> <66da.449fa326.573d6@clunker.homenet> Subject: Re: FA KEITHLEY 610C ELECTROMETER, PICO AMMETER COULOMB METER Plus Message-ID: Date: Thu, 29 Jun 2006 12:41:10 GMT "Roger leighton" wrote in message news:CqKdnVa_zu48ND_ZRVny1w@bt.com... >> Just remember the Milikan experiment... > > Please don't mention Spike on here ... What about a Bolt through the Nose? KW Article: 97776 of rec.radio.amateur.homebrew Subject: EARN CASH WHILE SAVING GAS From: "Gas Savers" Date: Thu, 29 Jun 2006 13:12:24 -0400 Message-ID: <1151600658_8587@sp6iad.superfeed.net> Looking to supplement your income or even change careeers. distributors needed all over the world. Take a look at this website and start earning real money in no time. The tablets really work and the income will continue to grow. This company is new and is growing leaps and bounds. Get in now. www.ransue.myffi.biz ----== Posted via Newsfeeds.Com - Unlimited-Unrestricted-Secure Usenet News==---- http://www.newsfeeds.com The #1 Newsgroup Service in the World! 120,000+ Newsgroups ----= East and West-Coast Server Farms - Total Privacy via Encryption =---- Article: 97777 of rec.radio.amateur.homebrew From: David Snowdon Subject: Re: Questions about I.F. Transformers Date: Thu, 29 Jun 2006 20:04:38 -0400 Message-ID: References: <1151624454.814545.127930@p79g2000cwp.googlegroups.com> Jody wrote: > I can't seem to find any I.F. transformers for 465 KHZ. I was wondering > if you can use the 455 khz ones instead without changing any other > components. I'm building a reciever that calls for 465. Can a 455 be > tuned this high using the slug? or does anyone know of a source for > these parts. Any advice would be greatly appreciated. > Most of these IF xformers have a fixed capacitor on the bottom of the device. You can remove it, measure it's value, and place a capacitor of a slightly lower value in its place. David, VA3DKS Article: 97778 of rec.radio.amateur.homebrew From: nospam@nouce.bellatlantic.net Subject: Re: Questions about I.F. Transformers Message-ID: References: <1151624454.814545.127930@p79g2000cwp.googlegroups.com> Date: Fri, 30 Jun 2006 00:09:49 GMT On 29 Jun 2006 16:40:54 -0700, "Jody" wrote: >I can't seem to find any I.F. transformers for 465 KHZ. I was wondering >if you can use the 455 khz ones instead without changing any other >components. I'm building a reciever that calls for 465. Can a 455 be >tuned this high using the slug? or does anyone know of a source for >these parts. Any advice would be greatly appreciated. I've met very few that would not tune that far. It's easy enough to test beforehand if ther eis uncertainty. Allison Article: 97779 of rec.radio.amateur.homebrew From: David Subject: Mosfet RF Amp "sprogging" Message-ID: Date: Fri, 30 Jun 2006 01:20:52 GMT I am currently experimenting with construction of my first Dual-Gate Mosfet Amp. Below is an attempt to explain the circuit typology as best I can Freq = 148 MHz to 152 MHz Power supply is 8V, Bias on G2 is 4V. Source is grounded Drain has Variable inductor to Vcc and Cap to ground to form first stage of a double-tuned circuit. This then couples through a small cap to the second half of the DTC. RF input to Single tuned circuit with tapped capacitors attached to G1 of BF998. C1 to ground is 56pF, C2 to G1 is 15pF, L from G1 to ground is variable with nominal inductance of 85nH (tunes 75nH to 110nH), Q approx. 100 The Drain has the same type of inductor to Vcc (decoupled Vcc end). C3 is 18pF from drain to ground (This forms part of the double-tuned circuit on the output). Coupling to second half of DTC is 1pF. Second half of DTC C4 = 18pF to ground and L is same as previous inductors (85nH nom.). This will later go to G1 of a Dual-Gate Mosfet mixer but for testing I replaced the 15pF on second DTC with series 18pF and 56pF to form a capacitive divider down to 50 Ohms for my spectrum analyzer input. With this configuration the circuit will oscillate on its own when the input is removed. If I replace the Capo from drain to ground with a trim cap I can adjust it so the self-oscillation stops but as soon as I try to change the tuning of the inductor from drain to Vcc, it starts to oscillate on its own. If I remove the cap from drain to ground altogether, the oscillations stop but I almost the ability to tune the Inductor, it becomes extremely broad tuning.(The input inductor and output DTC inductor tune fine though). I have tried a series 33R between the Drain of the mosfet and the Inductor/Capacitor and this did not help. The measured gain with the capacitor removed was 17dB. Drain current was 4.8mA. 3dB bandwidth was 3.2MHz. The circuit is laid out "dead-bug" style on a flat bare PCB. I'm not sure if it is a layout problem or typology issue. I have seen damping used across tuned circuits in output stages of rf amps and may try this next. But, I would like to know what is happening because if I manage to stop the oscillation, I am not sure if it is marginal and will reappear with changes in temperature or drive level etc. Any help much appreciated. Regards David Article: 97780 of rec.radio.amateur.homebrew From: David Subject: MOSFET amp sprogging[2] Message-ID: <41%og.18624$ap3.1561@news-server.bigpond.net.au> Date: Fri, 30 Jun 2006 01:22:08 GMT BTW: The device is a BF998 SMD package. Article: 97781 of rec.radio.amateur.homebrew From: nospam@nouce.bellatlantic.net Subject: Re: Mosfet RF Amp "sprogging" Message-ID: References: Date: Fri, 30 Jun 2006 02:25:54 GMT On Fri, 30 Jun 2006 01:20:52 GMT, David wrote: >I am currently experimenting with construction of my first Dual-Gate >Mosfet Amp. > >Below is an attempt to explain the circuit typology as best I can > >Freq = 148 MHz to 152 MHz > >Power supply is 8V, Bias on G2 is 4V. Source is grounded > >Drain has Variable inductor to Vcc and Cap to ground to form first stage >of a double-tuned circuit. This then couples through a small cap to the >second half of the DTC. > >RF input to Single tuned circuit with tapped capacitors attached to G1 >of BF998. > >C1 to ground is 56pF, C2 to G1 is 15pF, L from G1 to ground is variable >with nominal inductance of 85nH (tunes 75nH to 110nH), Q approx. 100 > >The Drain has the same type of inductor to Vcc (decoupled Vcc end). >C3 is 18pF from drain to ground (This forms part of the double-tuned >circuit on the output). >Coupling to second half of DTC is 1pF. Second half of DTC C4 = 18pF to >ground and L is same as previous inductors (85nH nom.). > >This will later go to G1 of a Dual-Gate Mosfet mixer but for testing I >replaced the 15pF on second DTC with series 18pF and 56pF to form a >capacitive divider down to 50 Ohms for my spectrum analyzer input. > >With this configuration the circuit will oscillate on its own when the >input is removed. If I replace the Capo from drain to ground with a trim >cap I can adjust it so the self-oscillation stops but as soon as I try >to change the tuning of the inductor from drain to Vcc, it starts to >oscillate on its own. > >If I remove the cap from drain to ground altogether, the oscillations >stop but I almost the ability to tune the Inductor, it becomes extremely >broad tuning.(The input inductor and output DTC inductor tune fine though). > >I have tried a series 33R between the Drain of the mosfet and the >Inductor/Capacitor and this did not help. > >The measured gain with the capacitor removed was 17dB. Drain current was >4.8mA. 3dB bandwidth was 3.2MHz. > >The circuit is laid out "dead-bug" style on a flat bare PCB. I'm not >sure if it is a layout problem or typology issue. >I have seen damping used across tuned circuits in output stages of >rf amps and may try this next. But, I would like to know what is >happening because if I manage to stop the oscillation, I am not sure if >it is marginal and will reappear with changes in temperature or drive >level etc. > >Any help much appreciated. > >Regards > >David Usually DGFET amps are stable. But they are also very high gain. The likely culprit is the input can see the output (incidental coupling). I always build this with a shield partition right across the device and also a ferrite bead in the G2 lead near the deivce as possible (or for SMD in the Source leg bypass cap). These devices will take off at uhf due to gain and less then careful bypassing. That includes making sure the G2 bias resistor (Gate to DC source) does not couple RF back. As part of this also insure the input and output leads to the connector are short as possible or even coax. Allison Article: 97782 of rec.radio.amateur.homebrew From: David Subject: Re: Mosfet RF Amp "sprogging" References: Message-ID: <0%0pg.18680$ap3.7270@news-server.bigpond.net.au> Date: Fri, 30 Jun 2006 03:36:28 GMT Thanks for the feedback (no pun intended :) I appreciate it. I will add a shield between input and output circuit. I do remember seeing this in other designs. In my prototype construction I do have the input and output coils fairly close and in the same orientation so I imagine there very well could be coupling between them. the fact that the circuit oscillates very close to the tuned frequency is probably a clue that positive feedback between input and output is happening. The source is grounded so Drain - Gate seems feasible. I will also take the advice of adding a ferrite bead between G2 pin and the voltage divider for G2. (Currently 100k+100k with 1n decoupling). Can anyone suggest a reasonably simple method to determine noise figure of this stage ? I do not have a distortion meter. I have directional couplers, sig gens, sepctrum analyzer and digital power meter. Can I use these somehow ? Thanks in advance again Best regards David nospam@nouce.bellatlantic.net wrote: > On Fri, 30 Jun 2006 01:20:52 GMT, David > wrote: > >> I am currently experimenting with construction of my first Dual-Gate >> Mosfet Amp. >> >> Below is an attempt to explain the circuit typology as best I can >> >> Freq = 148 MHz to 152 MHz >> >> Power supply is 8V, Bias on G2 is 4V. Source is grounded >> >> Drain has Variable inductor to Vcc and Cap to ground to form first stage >> of a double-tuned circuit. This then couples through a small cap to the >> second half of the DTC. >> >> RF input to Single tuned circuit with tapped capacitors attached to G1 >> of BF998. >> >> C1 to ground is 56pF, C2 to G1 is 15pF, L from G1 to ground is variable >> with nominal inductance of 85nH (tunes 75nH to 110nH), Q approx. 100 >> >> The Drain has the same type of inductor to Vcc (decoupled Vcc end). >> C3 is 18pF from drain to ground (This forms part of the double-tuned >> circuit on the output). >> Coupling to second half of DTC is 1pF. Second half of DTC C4 = 18pF to >> ground and L is same as previous inductors (85nH nom.). >> >> This will later go to G1 of a Dual-Gate Mosfet mixer but for testing I >> replaced the 15pF on second DTC with series 18pF and 56pF to form a >> capacitive divider down to 50 Ohms for my spectrum analyzer input. >> >> With this configuration the circuit will oscillate on its own when the >> input is removed. If I replace the Capo from drain to ground with a trim >> cap I can adjust it so the self-oscillation stops but as soon as I try >> to change the tuning of the inductor from drain to Vcc, it starts to >> oscillate on its own. >> >> If I remove the cap from drain to ground altogether, the oscillations >> stop but I almost the ability to tune the Inductor, it becomes extremely >> broad tuning.(The input inductor and output DTC inductor tune fine though). >> >> I have tried a series 33R between the Drain of the mosfet and the >> Inductor/Capacitor and this did not help. >> >> The measured gain with the capacitor removed was 17dB. Drain current was >> 4.8mA. 3dB bandwidth was 3.2MHz. >> >> The circuit is laid out "dead-bug" style on a flat bare PCB. I'm not >> sure if it is a layout problem or typology issue. >> I have seen damping used across tuned circuits in output stages of >> rf amps and may try this next. But, I would like to know what is >> happening because if I manage to stop the oscillation, I am not sure if >> it is marginal and will reappear with changes in temperature or drive >> level etc. >> >> Any help much appreciated. >> >> Regards >> >> David > > Usually DGFET amps are stable. But they are also very high > gain. > > The likely culprit is the input can see the output (incidental > coupling). I always build this with a shield partition right across > the device and also a ferrite bead in the G2 lead near the deivce > as possible (or for SMD in the Source leg bypass cap). These > devices will take off at uhf due to gain and less then careful > bypassing. That includes making sure the G2 bias resistor > (Gate to DC source) does not couple RF back. As part of this > also insure the input and output leads to the connector are short > as possible or even coax. > > > Allison Article: 97783 of rec.radio.amateur.homebrew From: Roy Lewallen Subject: Re: Mosfet RF Amp "sprogging" Date: Thu, 29 Jun 2006 20:33:01 -0700 Message-ID: <12a96rj1pc6omaa@corp.supernews.com> References: Your bypasses from G2 to ground and from the top of the drain inductor to ground should be physically small, have very nearly zero lead length, and connect directly to the drain or the bottom of the drain resistor if used. Roy Lewallen, W7EL Article: 97784 of rec.radio.amateur.homebrew From: Alfred Green Subject: Re: FA KEITHLEY 610C ELECTROMETER, PICO AMMETER COULOMB METER Plus References: <8659g.23076$mX1.20976@newsfe2-gui.ntli.net> <66da.449fa326.573d6@clunker.homenet> Message-ID: Date: Thu, 29 Jun 2006 22:11:15 -0700 >>> >>> >> Just remember the Milikan experiment... > > > Please don't mention Spike on here ... > > You mean Milligna, the well-known typing error? 73 Alf MU8I "Puckoon" Article: 97785 of rec.radio.amateur.homebrew From: David Subject: Re: Mosfet RF Amp "sprogging" References: <12a96rj1pc6omaa@corp.supernews.com> Message-ID: Date: Fri, 30 Jun 2006 05:27:44 GMT I have applied the suggestions and still can't manage to "tame the beast". As long as the cap to ground from drain is in circuit the amp becomes unstable at oscillates close to the centre frequency. If I remove the cap the amp settles down but I loose tuning of the drain circuit and the gain drops down. I have a picture of the layout and schematic if anyone would be prepared to take a look and see if there is something obvious. The shield is placed right across the top of the BF998 to separate input >from output. All component leads are cut as close to the component body as possible. I also added another shield between G2 and the input circuit so the input now is totally isolated from the rest of the ckt Regards David Roy Lewallen wrote: > Your bypasses from G2 to ground and from the top of the drain inductor > to ground should be physically small, have very nearly zero lead length, > and connect directly to the drain or the bottom of the drain resistor if > used. > > Roy Lewallen, W7EL Article: 97786 of rec.radio.amateur.homebrew From: David Subject: The beast (Dual gate Mosfet RF Amp) is settling down References: <12a96rj1pc6omaa@corp.supernews.com> Message-ID: <5w3pg.18735$ap3.2463@news-server.bigpond.net.au> Date: Fri, 30 Jun 2006 06:28:17 GMT I have conducted further investigation and discovered the following 1. Coupling between tuned circuits in DTC was a little high (reduce this >from 1pF to 0.5pF) 2. The Cap from Drain to ground (1st tuned ckt in DTC) was a little large. Reduced this to 10pF from 15pF. These changes enable smooth tuning of each inductor without any surprises. Gain has shot up to around 24dB and 3dB bandwidth is around 3.5MHz at 151 MHz Fo. What I do notice is that when I remove the input cable from the signal generator, the circuit starts to oscillate. If I terminate the floating cable with say a 6dB attenuator, the oscillation stops. Should I have something in front of the Single tuned input circuit such as a RFC, 3dB resistive pad or LPF to define input impedance ? Or is it maybe just the input floating as the Tapped capacitor divider has nothing to ground on the input side (FET side of course has the inductor to ground). Thanks Regards David David wrote: > I have applied the suggestions and still can't manage to "tame the beast". > > As long as the cap to ground from drain is in circuit the amp becomes > unstable at oscillates close to the centre frequency. > > If I remove the cap the amp settles down but I loose tuning of the drain > circuit and the gain drops down. > > I have a picture of the layout and schematic if anyone would be prepared > to take a look and see if there is something obvious. > > The shield is placed right across the top of the BF998 to separate input > from output. > All component leads are cut as close to the component body as possible. > > I also added another shield between G2 and the input circuit so the > input now is totally isolated from the rest of the ckt > > Regards > > David > > Roy Lewallen wrote: >> Your bypasses from G2 to ground and from the top of the drain inductor >> to ground should be physically small, have very nearly zero lead >> length, and connect directly to the drain or the bottom of the drain >> resistor if used. >> >> Roy Lewallen, W7EL Article: 97787 of rec.radio.amateur.homebrew From: "Eamon Skelton" Subject: Re: Mosfet RF Amp "sprogging" References: Message-ID: Date: Fri, 30 Jun 2006 08:02:41 GMT On Fri, 30 Jun 2006 03:36:28 +0000, David wrote: > Thanks for the feedback (no pun intended I appreciate it. > > I will add a shield between input and output circuit. I do remember > seeing this in other designs. In my prototype construction I do have the > input and output coils fairly close and in the same orientation so I > imagine there very well could be coupling between them. I had a similar problem with a 2M RF amp. I cured it by reversing the winding direction of one of the inductors. > Can anyone suggest a reasonably simple method to determine noise figure > of this stage ? I'm a bit reluctant to suggest a method that I haven't tried mysef, but you should be able to calculate NF by measuring the receiver noise output with a hot and cold resistor connected to the input. The usual method involves boiling water and melting ice. http://tinyurl.com/psdfo 73, Ed. EI9GQ. -- Remove 'X' to reply by e-mail. Linux 2.6.17 Article: 97788 of rec.radio.amateur.homebrew From: Roy Lewallen Subject: Re: Spurs on mixer output Date: Fri, 30 Jun 2006 11:53:16 -0700 Message-ID: <12aasp1i154uoad@corp.supernews.com> References: <9c0u7e.qnd.ln@tg6124.ab0wr.net> <1uudnfjaxZcAkjjZnZ2dnUVZ_vWdnZ2d@comcast.com> Pete KE9OA wrote: >. . . > In conclusion, make sure that the IMD isn't being generated in your test > setup, and make sure that you are not exceeding the recommended RF input > level to the SBL-1. A quick test for spurs being generated by the spectrum analyzer is to increase the spectrum analyzer input attenuation by 10 dB. Real spurs will drop 10 dB. Most spurs generated by the analyzer will drop a greater amount -- 20 dB if they're second order, 30 dB if they're third order, and so forth. If any spurs do drop more than 10 dB, you have to reduce the SA attenuator setting or the input signal level to the SA -- at least the level of the signal(s) generating the spurs. Roy Lewallen, W7EL Article: 97789 of rec.radio.amateur.homebrew From: "Steve N." Subject: Re: Mosfet RF Amp "sprogging" Date: Fri, 30 Jun 2006 13:18:45 -0500 Message-ID: References: <0%0pg.18680$ap3.7270@news-server.bigpond.net.au> "Eamon Skelton" wrote in message news:BU4pg.10810$j7.315106@news.indigo.ie... > On Fri, 30 Jun 2006 03:36:28 +0000, David wrote: > > > Thanks for the feedback (no pun intended I appreciate it. > > > > I will add a shield between input and output circuit. I do remember > > seeing this in other designs. In my prototype construction I do have the > > input and output coils fairly close and in the same orientation so I > > imagine there very well could be coupling between them. > > > I had a similar problem with a 2M RF amp. I cured it by > reversing the winding direction of one of the inductors. > > > > Can anyone suggest a reasonably simple method to determine noise figure > > of this stage ? > > I'm a bit reluctant to suggest a method that I haven't tried > mysef, but you should be able to calculate NF by measuring the > receiver noise output with a hot and cold resistor connected > to the input. The usual method involves boiling water and > melting ice. http://tinyurl.com/psdfo > > 73, Ed. EI9GQ. > David, I don't know your technical level, but here goes. I thought the dual gate is a type of cascode arrangement and should be stable owing to the isolation of the "top" device... Anyway... You are very correct about trying to "band-aid" it with de-Q'ing resistors. You need to find the root cause, not hope a patch works. You are well aware of and trying to solve a possible proximity feedback issue, so I won't go there. It is not clear what your term "sprogging" may mean. There was a term "Squeeging" which referred to oscillation or what is also called regen(regeneration) which is typically used for dirty (sideband-type), rather than clean (single frequency) oscillation. Is the oscillation a clean, oscillator signal (pure carrier), or does it have sidebands? If sidebands, are they clear and distinct or is it more of a wideband grunge/garbage? Are the sidebands mirrored on both sides or are they lopsided? These are all clues. If you have regular sidebands or grunge, you have a low frequency oscillation component and need to also look at bypassing. 33-200 ohms or a ferrite bead in series with a bypass can help diagnose it. If the sidebands are unequal, there are most likely both AM and FM components to the oscillation. Putting a regular scope on the supply or other places which are supposed to be bypassed might see the signal, helping to ID the cause. Be aware that two bypasses in parallel, of different size, can become a tuned circuit and therefore a high impedance at frequencies where the larger one is above self resonance and appears inductive. Pay extreemly close attention to the ground currents for the input and output circuitry. You want to have an absolute minimum of common path for these. I didn't see anything in your circuit description about the FET source. If it is self biased with a resistor & cap combination or what, but >from the source you should have two distinct paths in the ground you have to the respectice components tith no length of this "ground current path" in common - where both currents share a common path. you can even cut the PCB so there are two distinct ground planes which only meet at the FET source or its resistor/bypass cap. Watch the power supply side pretty much the same. Where does the Drain bypass connect to the plane? Hope this helps. 73, Steve, K9DCI Article: 97790 of rec.radio.amateur.homebrew From: "Steve N." Subject: Re: Spurs on mixer output Date: Fri, 30 Jun 2006 13:23:58 -0500 Message-ID: References: <9c0u7e.qnd.ln@tg6124.ab0wr.net> <1uudnfjaxZcAkjjZnZ2dnUVZ_vWdnZ2d@comcast.com> This didn't sound like the problem if I read it correctly, but... To test for analyzedr generated effects, switch-in 10 dB of attenuatin in FRONT of the analyzer mixer (not in the analyzer IF). If the garbage drops more than 10dB (like 20 or 30) then you are over driving the analyzer. If it is coming from outside, then you'll se dB for dB changes. 73, Steve, K9DCI Ain't the math of nonlinearity great? "Pete KE9OA" wrote in message news:1uudnfjaxZcAkjjZnZ2dnUVZ_vWdnZ2d@comcast.com... > What kind of spectrum analyzer are you using? What are the front end > attenuator settings on the spectrum analyzer? What is your reference level? > All of these things, especially the front end attenuator settings, can > affect your result. If the 1st mixer in the spectrum analyzer is driven into > nonlinearity, you can see all kinds of IMD products that are generated in > the analyzer itself. > Also, why are you doing this test with the RF port of the mixer terminated > in 50 Ohms? This type of termination is only used when doing either return > loss tests or noise balance tests. > If you are driving the SBL-1 mixer with +7 to +9dBm of LO level and you are > driving the RF port with a signal that is at least 20dB below the 1dB > compression point of the SBL-1, the main things you should see at the I.F. > port are a supressed LO signal, an upper sideband that is about 7dB lower in > level than the RF injection level, and a lower sideband that is also about > 7dB lower in level than the RF injection level. > The 1dB compression point on the SBL-1 is about 0dBm, so I would set the > level to the RF port at -20dBm. If you go above this level, you will see > higher conversion loss, and possibly more IMD products at the I.F. port of > the mixer. > In conclusion, make sure that the IMD isn't being generated in your test > setup, and make sure that you are not exceeding the recommended RF input > level to the SBL-1. > > Pete > > wrote in message > news:p9o5a21152qsldg22fqccf0tm1ba7grf2d@4ax.com... > > On Wed, 28 Jun 2006 07:43:20 -0500, tim gorman > > wrote: > > > >>john wilkinson wrote: > >> > >>> > >>> > >>> Hi, > >>> If I feed my second mixer into a spectrum analyser, and inject a > >>> 44.545MHz > >>> LO, with no power to the first IF stage, I see spurs at about 48-50KHz > >>> intervals on the mixer output, from 0 to the 455KHz normal output freq. > > > >> > >>> The mixer is an SBL-1. > >>> > >>> Any ideas as to where these are comming from? > >>> > >>> Best regards, > >>> John > >> > >>A couple of observations. > >> > >>If you simply disconnected the second mixer from the 1st mixer then it > >>sounds like you do not have the output of the 1st mixer properly > >>terminated. Unless, that is, the spectrum analyzer provides a good 50ohm > >>termination in the probe. The SBL-1 is a double-balanced mixer but in > >>order > >>to get the "balance" to work right you must properly terminate *all* > >>ports. > >>Otherwise all kinds of impedances can be "thrown" back to the other > >>ports - > >>causing all kinds of problems with attached LO's and RF stages. > >> > >>Regularly spaced spurs from DC to 455khz does not sound like spurious > >>mixing > >>products. It sounds more like an oscillator being driven into saturation > >>causing square waves to be produced which are providing regular harmonic > >>outputs. This could be a product of poor terminations on the mixer ports. > > > > Tim, the LO is 45.455 (or 44.545) either way there should be no LF > > outputs from the mixer below the LO injection unless it's a spur on > > the LO. > > > >>Directly connecting the output of a SBL-1 to the input of another mixer, > >>even another SBL-1, is not recommended either. The SBL-1 does not have > >>built-in terminations. A good, symmetric, 50ohm 3db pad between the stages > >>would provide a much better setup and would not significantly impact your > >>overall noise factor. Be sure and connect your spectrum analyzer to the > >>far > >>side of the pad. > > > > Thats true though his testing is with a 20db IF after it and one would > > hope that does present a 50ohm match to the IF port. Usually if the > > poarts are badly matched the mixing spurs are greater and the port > > to port isolation go to pot. If the only thing going in is the LO > > then likely the LO is the source but if there is gain flollowing then > > the gain stage is also suspect. > > > > I've worked with enough SBL1 and MD108s and all their similar DBMS > > to know the SBL1 in this case is not the offendor Even if > > misterminated. Likely causes are the 45mhz filter is looking reactive > > to the IF amp and the IF is unstable (makes a fine OSC) or there is > > some other source of RF that is unaccounted for (spurs). > > > > > > Allison > > Kb!GMX > > Article: 97791 of rec.radio.amateur.homebrew From: nospam@nouce.bellatlantic.net Subject: Re: Self-heating of crystal in inverter oscillator Message-ID: References: Date: Fri, 30 Jun 2006 21:49:43 GMT On Fri, 30 Jun 2006 15:48:03 -0500, Ben Jackson wrote: >I've got a 74HC86 (quad XOR) and I'm using 2 of the gates (with one input >tied high) to make inverter oscillators. One crystal at 14.85MHz in a >SMT package was relatively easy to start up and stabilize. The 25MHz >crystal (in a short can package) was very sensitive to Rs (series resistor >between the inverter output and one leg of the crystal) and low supply >voltage. To get it to start reliably I ended up with Rs=110 @ 5V. The >whole thing is drawing about 25mA. > >The problem I have is that the 74HC86 and 25MHz crystal seem to warm >up quickly and cause the 25MHz to drop by about 200Hz. This oscillator >isn't intended to be on for long periods of time, so I'd like to avoid >that. I've isolated those two parts by a combination of heating and >cooling components to see which contribute the most (the temp swing is >too small for me to feel, I'm just warming with a finger and cooling >with a puff of compressed air). > >So if I'm putting 15mA+ into that crystal, is that unusually high? >What would be a typical amount for such an oscillator? Is there >anything I can do about the effects of chip heating (I'm assuming >the gate capacitance is going up as it heats)? >From a stability factor point of view those "inverter" based oscillators are amoung the worst. I doubt it's all crystal heating and I bet there are parameter shifts in the "chip" as it warms up operating at high frequency like that. Also If you drive the crystal hard like they do (15ma!!!) bad things happen. Those circuits are OK for micros and other less critical apps. I suggest a discrete Bipolar or FET where you can control the operating point of the device better. Allison Article: 97792 of rec.radio.amateur.homebrew From: nospam@nouce.bellatlantic.net Subject: Re: Spurs on mixer output Message-ID: References: <9c0u7e.qnd.ln@tg6124.ab0wr.net> <1uudnfjaxZcAkjjZnZ2dnUVZ_vWdnZ2d@comcast.com> Date: Fri, 30 Jun 2006 21:54:39 GMT On Fri, 30 Jun 2006 06:48:45 -0500, "Pete KE9OA" wrote: >What kind of spectrum analyzer are you using? What are the front end I'm not using one the author of the thread is. >attenuator settings on the spectrum analyzer? What is your reference level? Ask him not me. >All of these things, especially the front end attenuator settings, can >affect your result. If the 1st mixer in the spectrum analyzer is driven into >nonlinearity, you can see all kinds of IMD products that are generated in >the analyzer itself. >Also, why are you doing this test with the RF port of the mixer terminated >in 50 Ohms? This type of termination is only used when doing either return >loss tests or noise balance tests. >If you are driving the SBL-1 mixer with +7 to +9dBm of LO level and you are >driving the RF port with a signal that is at least 20dB below the 1dB >compression point of the SBL-1, the main things you should see at the I.F. >port are a supressed LO signal, an upper sideband that is about 7dB lower in >level than the RF injection level, and a lower sideband that is also about >7dB lower in level than the RF injection level. >The 1dB compression point on the SBL-1 is about 0dBm, so I would set the >level to the RF port at -20dBm. If you go above this level, you will see >higher conversion loss, and possibly more IMD products at the I.F. port of >the mixer. >In conclusion, make sure that the IMD isn't being generated in your test >setup, and make sure that you are not exceeding the recommended RF input >level to the SBL-1. > >Pete You top posted to a reply that I'd posted to and your context is way off as a result. Go bat to the root of the thread and read the posting again. Briefly, he's seeing spurs every 25 or 50 khz with a LO in the 45mhz region and NO RF on the input (unterminated RF port). Allison > > wrote in message >news:p9o5a21152qsldg22fqccf0tm1ba7grf2d@4ax.com... >> On Wed, 28 Jun 2006 07:43:20 -0500, tim gorman >> wrote: >> >>>john wilkinson wrote: >>> >>>> >>>> >>>> Hi, >>>> If I feed my second mixer into a spectrum analyser, and inject a >>>> 44.545MHz >>>> LO, with no power to the first IF stage, I see spurs at about 48-50KHz >>>> intervals on the mixer output, from 0 to the 455KHz normal output freq. >> >>> >>>> The mixer is an SBL-1. >>>> >>>> Any ideas as to where these are comming from? >>>> >>>> Best regards, >>>> John >>> >>>A couple of observations. >>> >>>If you simply disconnected the second mixer from the 1st mixer then it >>>sounds like you do not have the output of the 1st mixer properly >>>terminated. Unless, that is, the spectrum analyzer provides a good 50ohm >>>termination in the probe. The SBL-1 is a double-balanced mixer but in >>>order >>>to get the "balance" to work right you must properly terminate *all* >>>ports. >>>Otherwise all kinds of impedances can be "thrown" back to the other >>>ports - >>>causing all kinds of problems with attached LO's and RF stages. >>> >>>Regularly spaced spurs from DC to 455khz does not sound like spurious >>>mixing >>>products. It sounds more like an oscillator being driven into saturation >>>causing square waves to be produced which are providing regular harmonic >>>outputs. This could be a product of poor terminations on the mixer ports. >> >> Tim, the LO is 45.455 (or 44.545) either way there should be no LF >> outputs from the mixer below the LO injection unless it's a spur on >> the LO. >> >>>Directly connecting the output of a SBL-1 to the input of another mixer, >>>even another SBL-1, is not recommended either. The SBL-1 does not have >>>built-in terminations. A good, symmetric, 50ohm 3db pad between the stages >>>would provide a much better setup and would not significantly impact your >>>overall noise factor. Be sure and connect your spectrum analyzer to the >>>far >>>side of the pad. >> >> Thats true though his testing is with a 20db IF after it and one would >> hope that does present a 50ohm match to the IF port. Usually if the >> poarts are badly matched the mixing spurs are greater and the port >> to port isolation go to pot. If the only thing going in is the LO >> then likely the LO is the source but if there is gain flollowing then >> the gain stage is also suspect. >> >> I've worked with enough SBL1 and MD108s and all their similar DBMS >> to know the SBL1 in this case is not the offendor Even if >> misterminated. Likely causes are the 45mhz filter is looking reactive >> to the IF amp and the IF is unstable (makes a fine OSC) or there is >> some other source of RF that is unaccounted for (spurs). >> >> >> Allison >> Kb!GMX > Article: 97793 of rec.radio.amateur.homebrew From: David Subject: Re: Mosfet RF Amp "sprogging" References: <0%0pg.18680$ap3.7270@news-server.bigpond.net.au> Message-ID: Date: Fri, 30 Jun 2006 23:46:14 GMT Thanks all for your input into this issue. I appreciate all the feedback I have received. I do like to discover and understand the mechanism for this issue so I can avoid it next time. "Sprogging" was probably not the best term to use afterall. The unwanted response is a clean carrier with no sidebands. This carrier appears within the tuning band of the amp tuned circuits and moves as either the input tuning or Drain tuning is adjusted. The Source is connected to ground plane. The circuit now only just starts to produce a very low level signal (maybe around 60 dB down) when I unplug the input cable from the signal generator. If I terminate the floating cable with a 50 Ohm attenuator, the oscillation stops. The most improvement has been achieved by addition of shielding between Input circuit and drain circuit. I suspect that I am getting radiated signal fed back. I also suppose that as long as the path loss between drain and input is greater than the gain of the amp then the circuit should not be able to oscillate. One other issue I were considering was that even though the circuit is built with very short leads directly on a continuous ground plane (PCB), Some "Pads" have been made by cutting away copper. But because the PCB is double sided, I wonder if the interaction between these pads make the lower ground plane and pads act like a capacitor (ie. energy coupled >from the pads into the lower ground plane and up into other pads through capacitive coupling). Maybe if it was single sided board or I add heaps of track pins from top to bottom layer would prove if this was the case. Another thing is the coils do not have their own shields so they probably act like antennas. I think it would be prudent to use only shielded cans as I cannot always ensure large physical distance between them. Regards David Steve N. wrote: > "Eamon Skelton" wrote in message > news:BU4pg.10810$j7.315106@news.indigo.ie... >> On Fri, 30 Jun 2006 03:36:28 +0000, David wrote: >> >>> Thanks for the feedback (no pun intended I appreciate it. >>> >>> I will add a shield between input and output circuit. I do remember >>> seeing this in other designs. In my prototype construction I do have the >>> input and output coils fairly close and in the same orientation so I >>> imagine there very well could be coupling between them. >> >> I had a similar problem with a 2M RF amp. I cured it by >> reversing the winding direction of one of the inductors. >> >> >>> Can anyone suggest a reasonably simple method to determine noise figure >>> of this stage ? >> I'm a bit reluctant to suggest a method that I haven't tried >> mysef, but you should be able to calculate NF by measuring the >> receiver noise output with a hot and cold resistor connected >> to the input. The usual method involves boiling water and >> melting ice. http://tinyurl.com/psdfo >> >> 73, Ed. EI9GQ. >> > > David, > I don't know your technical level, but here goes. I thought the dual > gate is a type of cascode arrangement and should be stable owing to the > isolation of the "top" device... Anyway... > > You are very correct about trying to "band-aid" it with de-Q'ing resistors. > You need to find the root cause, not hope a patch works. You are well aware > of and trying to solve a possible proximity feedback issue, so I won't go > there. > > It is not clear what your term "sprogging" may mean. There was a term > "Squeeging" which referred to oscillation or what is also called > regen(regeneration) which is typically used for dirty (sideband-type), > rather than clean (single frequency) oscillation. > > Is the oscillation a clean, oscillator signal (pure carrier), or does it > have sidebands? > If sidebands, are they clear and distinct or is it more of a wideband > grunge/garbage? > Are the sidebands mirrored on both sides or are they lopsided? > These are all clues. > > If you have regular sidebands or grunge, you have a low frequency > oscillation component and need to also look at bypassing. 33-200 ohms or a > ferrite bead in series with a bypass can help diagnose it. > If the sidebands are unequal, there are most likely both AM and FM > components to the oscillation. Putting a regular scope on the supply or > other places which are supposed to be bypassed might see the signal, helping > to ID the cause. > > Be aware that two bypasses in parallel, of different size, can become a > tuned circuit and therefore a high impedance at frequencies where the larger > one is above self resonance and appears inductive. > > Pay extreemly close attention to the ground currents for the input and > output circuitry. You want to have an absolute minimum of common path for > these. I didn't see anything in your circuit description about the FET > source. If it is self biased with a resistor & cap combination or what, but > from the source you should have two distinct paths in the ground you have to > the respectice components tith no length of this "ground current path" in > common - where both currents share a common path. you can even cut the PCB > so there are two distinct ground planes which only meet at the FET source or > its resistor/bypass cap. > Watch the power supply side pretty much the same. Where does the Drain > bypass connect to the plane? > > Hope this helps. > 73, Steve, K9DCI > > Article: 97794 of rec.radio.amateur.homebrew From: nospam@nouce.bellatlantic.net Subject: Re: Mosfet RF Amp "sprogging" Message-ID: References: <0%0pg.18680$ap3.7270@news-server.bigpond.net.au> Date: Sat, 01 Jul 2006 00:33:51 GMT On Fri, 30 Jun 2006 23:46:14 GMT, David wrote: >Thanks all for your input into this issue. I appreciate all the feedback >I have received. > >I do like to discover and understand the mechanism for this issue so I >can avoid it next time. > >"Sprogging" was probably not the best term to use afterall. > >The unwanted response is a clean carrier with no sidebands. >This carrier appears within the tuning band of the amp tuned circuits >and moves as either the input tuning >or Drain tuning is adjusted. > >The Source is connected to ground plane. > >The circuit now only just starts to produce a very low level signal >(maybe around 60 dB down) when I unplug the input cable from >the signal generator. If I terminate the floating cable with a 50 Ohm >attenuator, the oscillation stops. > >The most improvement has been achieved by addition of shielding between >Input circuit and drain circuit. > >I suspect that I am getting radiated signal fed back. I also suppose >that as long as the path loss between drain and input is greater than >the gain of the amp then the circuit should not be able to oscillate. You may try changing the input coil (less L and more C) and see if that helps. > >One other issue I were considering was that even though the circuit is >built with very short leads directly on a continuous ground plane (PCB), >Some "Pads" have been made by cutting away copper. But because the PCB >is double sided, I wonder if the interaction between these pads make the >lower ground plane and pads act like a capacitor (ie. energy coupled >from the pads into the lower ground plane and up into other pads through >capacitive coupling). Grount the top to the bottom of two sided boards. I use foil or braid to wrap the edges. Also add a few holes and put wires from top to bottom near the source lead. Next time rather than cutting pads in the board try this, Cut tiny islands of PCB material and super glue them down. Then you have isolated pads for SMT parts. For devices like BF998 in SMT I've used board "chips" that are 0.1x0.2 inch and that works fine. FYI when I used that device the source has a 100 ohm resistor to ground and the bypass cap is .001(for 6m) with a ferrite bead on the non grounded lead. That is a "stock" circuit for DG fets and it seems well behaved to me. >Maybe if it was single sided board or I add heaps of track pins from top >to bottom layer would prove if this was the case. Do the latter. If you wrap the edges and put pins through near grounded compnents that's enough (likely only a few needed). >Another thing is the coils do not have their own shields so they >probably act like antennas. I think it would be prudent to use only >shielded cans as I cannot always ensure large physical distance between >them. That helps. Also make sure the output side has a valid load on it too. Do not load or resistive pad the input as that degrades the NF and gain. Allison > >Regards > >David > >Steve N. wrote: >> "Eamon Skelton" wrote in message >> news:BU4pg.10810$j7.315106@news.indigo.ie... >>> On Fri, 30 Jun 2006 03:36:28 +0000, David wrote: >>> >>>> Thanks for the feedback (no pun intended I appreciate it. >>>> >>>> I will add a shield between input and output circuit. I do remember >>>> seeing this in other designs. In my prototype construction I do have the >>>> input and output coils fairly close and in the same orientation so I >>>> imagine there very well could be coupling between them. >>> >>> I had a similar problem with a 2M RF amp. I cured it by >>> reversing the winding direction of one of the inductors. >>> >>> >>>> Can anyone suggest a reasonably simple method to determine noise figure >>>> of this stage ? >>> I'm a bit reluctant to suggest a method that I haven't tried >>> mysef, but you should be able to calculate NF by measuring the >>> receiver noise output with a hot and cold resistor connected >>> to the input. The usual method involves boiling water and >>> melting ice. http://tinyurl.com/psdfo >>> >>> 73, Ed. EI9GQ. >>> >> >> David, >> I don't know your technical level, but here goes. I thought the dual >> gate is a type of cascode arrangement and should be stable owing to the >> isolation of the "top" device... Anyway... >> >> You are very correct about trying to "band-aid" it with de-Q'ing resistors. >> You need to find the root cause, not hope a patch works. You are well aware >> of and trying to solve a possible proximity feedback issue, so I won't go >> there. >> >> It is not clear what your term "sprogging" may mean. There was a term >> "Squeeging" which referred to oscillation or what is also called >> regen(regeneration) which is typically used for dirty (sideband-type), >> rather than clean (single frequency) oscillation. >> >> Is the oscillation a clean, oscillator signal (pure carrier), or does it >> have sidebands? >> If sidebands, are they clear and distinct or is it more of a wideband >> grunge/garbage? >> Are the sidebands mirrored on both sides or are they lopsided? >> These are all clues. >> >> If you have regular sidebands or grunge, you have a low frequency >> oscillation component and need to also look at bypassing. 33-200 ohms or a >> ferrite bead in series with a bypass can help diagnose it. >> If the sidebands are unequal, there are most likely both AM and FM >> components to the oscillation. Putting a regular scope on the supply or >> other places which are supposed to be bypassed might see the signal, helping >> to ID the cause. >> >> Be aware that two bypasses in parallel, of different size, can become a >> tuned circuit and therefore a high impedance at frequencies where the larger >> one is above self resonance and appears inductive. >> >> Pay extreemly close attention to the ground currents for the input and >> output circuitry. You want to have an absolute minimum of common path for >> these. I didn't see anything in your circuit description about the FET >> source. If it is self biased with a resistor & cap combination or what, but >> from the source you should have two distinct paths in the ground you have to >> the respectice components tith no length of this "ground current path" in >> common - where both currents share a common path. you can even cut the PCB >> so there are two distinct ground planes which only meet at the FET source or >> its resistor/bypass cap. >> Watch the power supply side pretty much the same. Where does the Drain >> bypass connect to the plane? >> >> Hope this helps. >> 73, Steve, K9DCI >> >> Article: 97795 of rec.radio.amateur.homebrew From: larson@w6yx.stanford.edu (Alan Larson) Subject: Re: is an STA needed to transmit data on CB channel 40? Date: Sat, 1 Jul 2006 06:30:05 +0000 (UTC) Message-ID: References: <1150652485.685726.246160@c74g2000cwc.googlegroups.com> <1150742942.564318.271840@p79g2000cwp.googlegroups.com> In article <1150742942.564318.271840@p79g2000cwp.googlegroups.com> eternalsquire@comcast.net writes: >Thank you all for your suggestions. > >This is not a hoax. But I too find the need sufficiently implausible >that I feel a little bit queasy taking R&D fees for a cause like this >at $50 per hour. The only reason that I'm not mentioning the >consulting firm is that I could stand to get paid... and any money is >better than no money. And if I'm the king's coin then I ought to make >it work. > >I agree, Truck stops are a very good idea for commandeering CB's, but >you only find those in the exurbs.. Yes, other commercial radio >services could and maybe even should be drafted into this. The squad >lead could then determine the tradeoffs based on the availability of >foraged equipment. > >Allison, your idea of using the dummy loads to simulate fading over >distance is OUTSTANDING. I'll do it! > >Using dummy loads as a demo, I could then get the consulting firm to >ask the FCC for an STA for field tests. > >For my test rigs, I'm intending to plug in a laptop sound card I/O into >the SSB mic and headphone jacks. Therefore no type acceptance needed >because no mods. As soon as you plug in something other than the approved mike, you have probably broken type acceptance. >My brother says ideally in the scenario, each squad leader should only >need to carry a mini-CDROM in his or her pocket. The squad lead could >then commandeer a laptop, an SSB CB radio, and then use an abandoned >automobile as an electric generator for the laptop and radio. Antenna >would be flung over a 3 story office building. SSB CB radios are fairly rare nowdays. The microphone connection is non-standard, and won't directly wire to a sound card. A wire flung over a 3 story office building won't be matched. It will likely work poorly, or it may even fry the transmitter. >One of the reasons for this scenario is to lighten the overall squad >load and thereby increase the speed of response. That way each squad >could break into an abandoned store and then set up a first responder >posts. A 1 to 2 pound VHF radio will give better coverage, will function as they are going in, and will free up personnel labor for more important tasks. Wasting a person's time setting something like this up is more serious than carrying a small hand-held radio. Alan Article: 97796 of rec.radio.amateur.homebrew From: larson@w6yx.stanford.edu (Alan Larson) Subject: Re: is an STA needed to transmit data on CB channel 40? Date: Sat, 1 Jul 2006 06:33:41 +0000 (UTC) Message-ID: References: <1150742942.564318.271840@p79g2000cwp.googlegroups.com> <1150761212.462138.299280@y41g2000cwy.googlegroups.com> In article <1150761212.462138.299280@y41g2000cwy.googlegroups.com> eternalsquire@comcast.net writes: > >jimp@specsol.spam.sux.com wrote: >> eternalsquire@comcast.net wrote: > >> Let's see, all you have to do is find a bunch of laptops with 12V >> adapters, > >12V power is standard power jack for laptops No, it isn't. Many use higher voltages. > a bunch of CB radios with documentation on the mic input, > >The docs could be on the CD-ROM. Squad leader or designate >could read that using the laptop. > >> a soldering iron to make up a mic/laptop interface cable (assuming >> you can use the existing mic cable connector). >Shouldn't be too hard. > >> >> The only problem left is how to get the abandoned automobile to the >> top of the 3 story office building (if any are left standing in this >> disaster). >The feed could start at street level and connect to a dipole on the >rooftop. Carrying a 1 to 2 pound VHF radio in will provide communications all the way in. Using it will save a lot of personnel time that can be used for something more important that hacking together something with a CB that would work very poorly if at all. Conclusion: This must be a troll. I hope that nobody in our government is *STUPID* enough to fall for such a plan. Alan Article: 97797 of rec.radio.amateur.homebrew From: Paul Keinanen Subject: Re: Questions about I.F. Transformers Message-ID: References: <1151624454.814545.127930@p79g2000cwp.googlegroups.com> Date: Sat, 01 Jul 2006 11:33:57 +0300 On 29 Jun 2006 16:40:54 -0700, "Jody" wrote: >I can't seem to find any I.F. transformers for 465 KHZ. I was wondering >if you can use the 455 khz ones instead without changing any other >components. I'm building a reciever that calls for 465. What exactly specifies that the 465 kHz must be used ? Is there a frequency synthesiser or frequency counter with specifies a fixed 465 kHz offset ? If not, just run the local oscillator at a frequency 10 kHz lower to produce the 455 kHz IF and calibrate the scale accordingly. If this is a dual conversion receiver, change the second mixer oscillator frequency. Paul OH3LWR Article: 97798 of rec.radio.amateur.homebrew From: David Subject: Re: Mosfet RF Amp "sprogging" References: <0%0pg.18680$ap3.7270@news-server.bigpond.net.au> Message-ID: <5_upg.19499$ap3.6117@news-server.bigpond.net.au> Date: Sat, 01 Jul 2006 13:43:29 GMT Thanks for your input everyone. I re-constructed the layout using SMD components on a bare copper PCB. This time I changed the typology slightly and added 100R with 1n in the source of the BF998. I placed a 2k7 across the drain coil to set correct Rp for the DTC bandwidth. I also changed the tuning coils for fixed coils and tuned with variable caps instead. The circuit seems stable now. The Amp has total gain of 23dB (includes loss of the input filter and double tuned circuit). All caps are tuning properly with no unexpected behaviour. I have not yet added any shielding or connected vias from top to bottom plane of the PCB. The tuning range is almost as calculated (6MHz Bandwidth at Fo = 150 MHz). Does anyone know what an reasonable 1dB compression point would be for a the BF998 at 150 Mhz ? The drain current seems a bit low (about 3mA) and I think this may need increasing to get a reasonable dynamic range ? The gate 2 bias is currently 4V. This should not be pinching off the drain current at all. I wonder if the 100 Ohm in the source should be made smaller ? Any ideas. Thanks Regards David Highland Ham wrote: >> One other issue I were considering was that even though the circuit is >> built with very short leads directly on a continuous ground plane >> (PCB), Some "Pads" have been made by cutting away copper. But because >> the PCB is double sided, I wonder if the interaction between these >> pads make the lower ground plane and pads act like a capacitor (ie. >> energy coupled from the pads into the lower ground plane and up into >> other pads through capacitive coupling). >> >> Maybe if it was single sided board or I add heaps of track pins from >> top to bottom layer would prove if this was the case. > ============================== > With only having double sided PCB material I drill various holes and > bond the 2 planes at different locations by soldering wires on both planes. > For VHF/UHF circuits (in addition to the above) I line the circumference > of the material by folding 6mm wide thin (abt 0.2mm thick)copper strip > onto both planes and solder. I found a 'half a mile long ' roll of this > material at a flea market . > > Frank GM0CSZ / KN6WH Article: 97799 of rec.radio.amateur.homebrew From: nospam@nouce.bellatlantic.net Subject: Re: Mosfet RF Amp "sprogging" Message-ID: <0cvca2p5c8l02ljro604h9jegjc6esen8j@4ax.com> References: <0%0pg.18680$ap3.7270@news-server.bigpond.net.au> <5_upg.19499$ap3.6117@news-server.bigpond.net.au> Date: Sat, 01 Jul 2006 13:58:44 GMT On Sat, 01 Jul 2006 13:43:29 GMT, David wrote: >Thanks for your input everyone. > >I re-constructed the layout using SMD components on a bare copper PCB. >This time I changed the typology slightly and added 100R with 1n in the >source of the BF998. I placed a 2k7 across the drain coil to set correct >Rp for the DTC bandwidth. > >I also changed the tuning coils for fixed coils and tuned with variable >caps instead. > >The circuit seems stable now. The Amp has total gain of 23dB (includes >loss of the input filter and double tuned circuit). >All caps are tuning properly with no unexpected behaviour. > >I have not yet added any shielding or connected vias from top to bottom >plane of the PCB. > >The tuning range is almost as calculated (6MHz Bandwidth at Fo = 150 MHz). > >Does anyone know what an reasonable 1dB compression point would be for >a the BF998 at 150 Mhz ? The drain current seems a bit low (about 3mA) >and I think this may need increasing to get a reasonable dynamic range ? Before you get too concerned over the amps DR you need to consider that the RX following will be typically be degraded in DR by the amount of gain ahead of it. That would be true for most cases unless the RX has a IP if +10DBm or better. I haven't meaured many of those amps for DR but 1db compression is around a few DBm ( one was at +2dbm and the other was +5dbm output) by then most recievers are grossly overloaded. >The gate 2 bias is currently 4V. This should not be pinching off the >drain current at all. I wonder if the 100 Ohm in the source should be >made smaller ? Any ideas. FETs have good dynamic range for their current. You can lower the 100r but the increase in DR is small. You can also play with the bias to gate 2 (go for the high current side of peak gain). Allison > >Thanks > >Regards > >David > > > >Highland Ham wrote: >>> One other issue I were considering was that even though the circuit is >>> built with very short leads directly on a continuous ground plane >>> (PCB), Some "Pads" have been made by cutting away copper. But because >>> the PCB is double sided, I wonder if the interaction between these >>> pads make the lower ground plane and pads act like a capacitor (ie. >>> energy coupled from the pads into the lower ground plane and up into >>> other pads through capacitive coupling). >>> >>> Maybe if it was single sided board or I add heaps of track pins from >>> top to bottom layer would prove if this was the case. >> ============================== >> With only having double sided PCB material I drill various holes and >> bond the 2 planes at different locations by soldering wires on both planes. >> For VHF/UHF circuits (in addition to the above) I line the circumference >> of the material by folding 6mm wide thin (abt 0.2mm thick)copper strip >> onto both planes and solder. I found a 'half a mile long ' roll of this >> material at a flea market . >> >> Frank GM0CSZ / KN6WH Article: 97800 of rec.radio.amateur.homebrew From: nospam@nouce.bellatlantic.net Subject: Re: Self-heating of crystal in inverter oscillator Message-ID: <8vvca294jm11qma8glha502eu4rrmgqgkv@4ax.com> References: Date: Sat, 01 Jul 2006 14:04:33 GMT On Sat, 01 Jul 2006 02:23:19 -0500, Ben Jackson wrote: >On 2006-06-30, nospam@nouce.bellatlantic.net wrote: >> From a stability factor point of view those "inverter" based >> oscillators are amoung the worst. > >Good to know. I was trying to reduce part count -- the quad XOR provides >the two oscillators plus one mixer. > >> and I bet there are parameter shifts in the "chip" as it warms up > >The other parameter shift I was missing was droop in the 5V rail as >the 78L05 warmed up (rapidly!) and noise injected by a MAX202 charge >pump also on that 5V rail. I thought that regulator was just for an >(unused) LCD header, but I was wrong. Those added elements don't help. However I've used flavors (both TTL and CMOS) of the circuit and stability is only ok at best. One use was a simple freq counter (commercial purchase) and I could never get it to stay zeroed on WWV, it was always 100hz or more off every time I'd check it. I tried everything and finally pulled that out and added a simple transistor circuit. After than the error was usually less than a few hz. >> I suggest a discrete Bipolar or FET where you can control the >> operating point of the device better. > >If I can't tame this VCXO I will try that. This must be how Manhattan >prototyping branches off into "Ugly"... It do at that. ;) Allison Article: 97801 of rec.radio.amateur.homebrew From: "john graesser" Subject: Re: Using Garage for Ham Shack Date: Sat, 1 Jul 2006 09:36:40 -0500 Message-ID: <12ad1pqjm50l90b@corp.supernews.com> References: <1151699486.365534.315290@y41g2000cwy.googlegroups.com> "Alex" wrote in message news:1151699486.365534.315290@y41g2000cwy.googlegroups.com... > Hi Everyone, > > I hope to get my technician license for the first time in a month or > two, and I've been thinking of setting-up shop in the garage once I > start getting some radios and equipment. > > Some questions though, the garage is on the corner of our brick house > with one smaller window (facing front of house), two walls are interior > walls with other two being exterior (one having garage door). > > My thought is if I insulate the attic and the one exterior wall without > the garage door then replace my aging garage door with a better sealing > one, that should do the trick -- right? As for heating and cooling, > i'm in central texas, and our summers do get hot. I don't think our > A/C in the house could pump out enough cool air to cool an additional > 430sqft, so any suggestions for that? The only window is on front of > house, so don't want to use window unit. I have a radiant heater I've > used in there for winter, and it works well. > > Thanks for any suggestions or ideas ... we don't park our cars in the > garage, and I hope to build a small shead in the back yard for the > mowers and such -- so that's 430sqft of space that's going to waste. I'm also here in central TX and have the additional penalty in that I live in an apartment. My shack is in my car, it doesn't take up much room to install a vhf radio and an hf radio. I do have duplicates in the apartment in the event that the car is out of service. I just don't have the hf rig in the apt hooked up to an antenna full time since the manager is not ham friendly. If I want to work hf I just drive the car to the top of a hill and tune up, idling with the ac running it works just fine for the 9 months of summer, with the heater running for the 2 months of winter and with the windows open for each of the 2 weeks of spring and fall. If you are more interested in emergency operations, then tying yourself to your garage can be a negative. thanks, John. KC5DWD