The RC on the output of the zener trick works for white noise, but I think the freq jumps would be just as annoying.
Dennis AE6C On Sat, Jul 30, 2011 at 2:31 PM, Garey Barrell <k4...@mindspring.com> wrote: > Dennis - > > Well, I know "I" want to know more! I've been out of semis so long I'm > completely lost. I 'know' a lot of things, (Zeners are noisy,) but didn't > know 'why'! An engineering brain is a terrible thing to waste....... :-) > > > 73, Garey - K4OAH > Glen Allen, VA > > Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line > and TR-4/C Service Supplement CDs > <www.k4oah.com> > > > Dennis Monticelli wrote: > >> Hi Ron, >> Well, what we call a zener these days is actually not a zener (whose >> breakdown mechanism is actually quantum mechanical tunneling), but rather an >> avalanche breakdown diode. Electrons get rippped loose by the high electric >> fields at the PN junction interface, smack into other atoms, kick loose more >> electrons and pretty soon you've got something akin to a snow avalanche. >> This is an inherantly noisy process of generating current. When the PN >> junction is manufactured such that the avalanching occurs at the surface of >> the semiconductor chip that is bad for stability. Various mobile ions >> (often from the molding compound itself) migrate to the region of the >> breakdown under the influence of the attractive electric field. They >> accumlate there and alter the breakdown characteristic. The point of >> avalanche then tends to flit from one region to another, each region with a >> sightly different voltage value. Hence the net zener voltage jumps around >> in a random fashion. This is in addition to the normal white noise of >> avalanche. The worst I've ever seen is 500mV and more typically it is a few >> mV's or ten's of mV, but that is sufficient to shift an LC oscillator. >> A zener diode made in a sophisticated way can avoid the instability issue >> entirely but "burying" the PN junction below the surface of the chip. >> Probably more than you wanted to know :-) >> Dennis AE6C >> On Sat, Jul 30, 2011 at 11:32 AM, Ron <wd8...@yahoo.com <mailto: >> wd8...@yahoo.com>> wrote: >> >> Dennis, >> I would be interested in hearing more about the physics. Not sure if >> the rest of the list >> would be. >> >> I studied Electronics, and then ended up in computers. Kind of enjoy >> some good old college >> "lecture series" now and then. >> >> 73, >> Ron WD8SBB >> >> --- On *Sat, 7/30/11, Dennis Monticelli /<dennis.montice...@gmail.com >> <mailto:dennis.monticelli@**gmail.com <dennis.montice...@gmail.com>>>/* >> wrote: >> >> >> From: Dennis Monticelli <dennis.montice...@gmail.com <mailto: >> dennis.monticelli@**gmail.com <dennis.montice...@gmail.com>>> >> >> Subject: Re: [Drakelist] R-4A PTO: Confirmed it's the PTO. >> >> To: "Steve Wedge" <w1es1...@earthlink.net <mailto: >> w1es1...@earthlink.net**>> >> Cc: drakelist@zerobeat.net <mailto:drakelist@zerobeat.net**> >> >> Date: Saturday, July 30, 2011, 12:31 PM >> >> >> I know from my experience in the semiconductor business that zeners >> (especially those from >> a prior era) are notoriously noisy and can become outright unstable >> to varying degrees. You will not see this with a DVM or other >> averaging type instrument. You should put a >> scope on the zener and turn up the gain as high as the scope will >> go while setting the >> time base for anywhere from 1 to 100ms/div. Make sure your scope >> ground connection is >> right at the zener to keep stray pickup at a minimum. If it is >> unstable you will see the >> voltage jumping around in discrete steps. A typical zener will >> just exhibit "white" noise >> which looks like tall grass on the CRT. Both the discrete steps >> and the white noise will >> modulate the PTO. The steps manifest as annoying random freq >> shifts while the white >> noise just adds to the noise sidebands of the oscillator. The >> discrete jumps in zener >> voltage are understood in the physics but unless folks are truly >> interested in that stuff >> I won't go into it here. >> Not to scold the Drake design team (whom I respect) and maybe >> mostly because I witnessed >> how the sausage is actually made, but I would NEVER design a zener >> into a circuit as noise >> sensitive as an oscillator, mixer or preamp. I designed and built >> a homebrew antenna >> noise bridge. Guess what I used as the broadband noise source? >> Dennis AE6C >> >> On Fri, Jul 29, 2011 at 3:25 PM, Steve Wedge < >> w1es1...@earthlink.net >> >> <http://mc/compose?to=**w1es1...@earthlink.net<http://mc/compose?to=w1es1...@earthlink.net>>> >> wrote: >> >> Well, it has been a long, strange trip here. >> >> Just finished a little experiment with the PTO and my K3. >> First of all, the K3 is >> deaf as a post at 4.9 MHz ;-) but I did get enough of a signal >> through a scope probe >> hooked to the PTO output to confirm that it's the PTO that is >> shifting frequency. >> >> Having confirmed that, my next step will be replacing the 3000 >> pF and the zener - even >> though I'm fairly convinced the zener is okay (alright - I'll >> replace the 3000 pF >> first...). >> >> I have a sneaking suspicion that this may be one of the S.A.T. >> caps. If so, it's >> going to be interesting since I no longer have a capacitance >> meter. >> >> Steve Wedge, W1ES/4 >> >> "I can't complain, but sometimes I still do." >> - Joe Walsh >> >> If the above message appears, it came from Steve's Son of >> Laptop! >> ----- Original Message ----- From: "Garey Barrell" < >> k4...@mindspring.com >> >> <http://mc/compose?to=k4oah@**mindspring.com<http://mc/compose?to=k4...@mindspring.com> >> >> >> To: "Steve Wedge" <w1es1...@earthlink.net < >> http://mc/compose?to=**w1es1...@earthlink.net<http://mc/compose?to=w1es1...@earthlink.net> >> >> >> Cc: <drakelist@zerobeat.net <http://mc/compose?to=** >> drakelist@zerobeat.net <http://mc/compose?to=drakelist@zerobeat.net>>> >> >> Sent: Friday, July 29, 2011 3:21 PM >> Subject: Re: [Drakelist] R-4A PTO: It wasn't the transistors >> >> >> Steve - >> >> Yes, the PreMixer signal (V8) (BAND minus PTO) is the one >> that is piped back and >> forth between the two units. >> >> All you have to do is listen to the PTO signal itself on a >> separate receiver. "0" >> on the dial = 5.455 MHz, "500" = 4.955. The BFO crystal is >> 5.595 MHz. The BFO is >> a tube, V3, which I believe we swapped way back towards the >> beginning of this >> odyssey!! I also thought you had put a counter on the PTO, >> but I guess that's >> another 'project'. :-) I typically have three or four of >> these eMail projects >> going at one time, which is why I like to keep the entire >> thread together. Makes >> it easier to go back occasionally just to review just what >> path got us 'here'! :-) >> >> 73, Garey - K4OAH >> Glen Allen, VA >> >> Drake 2-B, 2-C/2-NT, 4-A, 4-B, C-Line >> and TR-4/C Service Supplement CDs >> <www.k4oah.com <http://www.k4oah.com/>> >> >> >> >> Steve Wedge wrote: >> >> You know, Garey, I've been thinking about the xtal >> oscillator. It would have >> to be part that doesn't get bandswitched - which would >> include THAT transistor. >> >> When the T-4X controls the frequency, it sounds great >> and never jumps >> frequency. In looking at the schematic, I have been >> aware that the two >> solid-state oscillators (PTO and LO for the band) get >> mixed in V8 (IIRC) and >> that this combination gets overridden by the output of >> the T-4X's premixer. >> >> Looks like I am going to need a counter to find out. I >> am loathe to dig into >> the T-4X because it's working so well and the PTO is >> much more difficult to >> remove from it due to the volume of wires in the area. >> >> 73, >> >> Steve, W1ES >> >> >> Date: Fri, 29 Jul 2011 13:31:12 -0400 >> From: Garey Barrell<k4...@mindspring.com >> >> <http://mc/compose?to=k4oah@**mindspring.com<http://mc/compose?to=k4...@mindspring.com>>> >> >> >> To: Richard >> Knoppow<1oldlens1@ix.netcom.**com<1oldle...@ix.netcom.com> >> >> <http://mc/compose?to=**1oldle...@ix.netcom.com<http://mc/compose?to=1oldle...@ix.netcom.com> >> >> >> Cc: drakelist@zerobeat.net <http://mc/compose?to=** >> drakelist@zerobeat.net <http://mc/compose?to=drakelist@zerobeat.net>> >> >> Subject: Re: [Drakelist] R-4A PTO: It wasn't the >> transistors >> (entirely) >> >> Message-ID:<4E32EE60.4060209@**mindspring.com<4e32ee60.4060...@mindspring.com> >> <http://mc/compose?to=**4E32EE60.4060209@mindspring.** >> com <http://mc/compose?to=4e32ee60.4060...@mindspring.com>>> >> >> Content-Type: text/plain; charset=ISO-8859-1; >> format=flowed >> >> Richard - >> >> Yes, one wonders...... :-) This type of >> 'dithering' is known in PTOs, but >> although much less >> common, a poor crystal oscillator such as the BAND or >> 2nd MIXER oscillators >> 'could' present the same >> way. >> >> >> >> ______________________________**_________________ >> Drakelist mailing list >> Drakelist@zerobeat.net <http://mc/compose?to=** >> Drakelist@zerobeat.net <http://mc/compose?to=Drakelist@zerobeat.net>> >> >> >> http://mailman.zerobeat.net/**mailman/listinfo/drakelist<http://mailman.zerobeat.net/mailman/listinfo/drakelist> >> >> >> >> -----Inline Attachment Follows----- >> >> >> ______________________________**_________________ >> Drakelist mailing list >> Drakelist@zerobeat.net <http://mc/compose?to=** >> Drakelist@zerobeat.net <http://mc/compose?to=Drakelist@zerobeat.net>> >> >> >> http://mailman.zerobeat.net/**mailman/listinfo/drakelist<http://mailman.zerobeat.net/mailman/listinfo/drakelist> >> >> >>
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