K2: RXVFO Waveform?
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While debugging a transmit output problem (cracked RFC13 found) I noticed
that although the input to U3 is a nice sine wave the output (RXVFO) is distorted. It has the proper gain (x2) but has what appears to be some higher order distortion on its way to the proper output level. Maybe second or third order. Definitely not oscillation. Power and ground to the IC is clean. Is this due to the TUF-1 load as the diodes begin to conduct? The input TXVFO is nice and clean so it makes me think the '1252 was put in this location just to handle the effect of the mixer non-linear load. The receiver sounds great on 40M. I'm going ahead and tuning up the receiver on the other bands while waiting on the choke. Or maybe I have another issue to debug... 73 jim ab3cv (pam shipped my rfc13 right after i called!!!) _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Here's a link to the pics I took of scope traces for TP1 aka RXVFO.
As I said the receiver sounds fine. I'm not used to working with CFA type amps driving low impedence nonlinear loads. Does this look OK? http://www1.snapfish.com/share/p=55201169346768265/l=239913880/g=15542617/cobrandOid=1000131/otsc=SYE/otsi=SALB 73 jim ab3cv _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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don't worry about creating an account or signing in. just click the "view
now" button. first time i've tried snapfish... 73 jim ab3cv _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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In reply to this post by Jim AB3CV
Jim,
> Does this look OK? > http://www1.snapfish.com/share/p=55201169346768265/l=239913880/g=15542617/co brandOid=1000131/otsc=SYE/otsi=SALB I think these waveforms are as expected when driving such a nonlinear load as the diode mixer. Also this correlates very well with the reported interference from strong near-by FM stations in 2002 due to harmonic mixer products, see e.g. http://www.ac6rm.net/mailarchive/html/elecraft-list/2002-05/msg00829.html There were many reports about this in May 2002, just search for FM in http://www.ac6rm.net/mailarchive/html/elecraft-list/2002-05/index.html and here are some possible explanations: http://www.ac6rm.net/mailarchive/html/elecraft-list/2002-05/msg00907.html http://www.ac6rm.net/mailarchive/html/elecraft-list/2002-06/msg00386.html http://www.ac6rm.net/mailarchive/html/elecraft-list/2002-06/msg00528.html 73 Sverre LA3ZA Unofficial Guide to K2 Modifications http://www.qslnet.de/member/la3za/K2/mod.html -- I am using the free version of SPAMfighter for private users. It has removed 1820 spam emails to date. Paying users do not have this message in their emails. Get the free SPAMfighter here: http://www.spamfighter.com _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Sverre:
Thanks for the historical FM interference research. At the suggestion of Bob, N5BZ, I recently made some measurements of my K2's sensitivity to responses of the form N*LO +/- 4915 KHz, via a short piece of exposed coaxial cable (a BNC-to-binding post adapter at the end of the cable), moving the cable end around, outside the K2's enclosure. N is an integer representing the harmonic number of the LO signal. I found responses up to 73 MHz (I stopped testing at that frequency, so I am not saying that higher frequency unwanted responses are not present). I found the strongest response when the cable end was near the right rear bottom of the enclosure, i.e., near the SO239 antenna connector. During the tests, the only connections to the K2 were the power supply and headphones. The antenna input was connected to a shorting cap. I could hear the unwanted signals with a signal generator output as low as -20 to -30 dBm. Since the signal generator's radiating element is only a binding post adapter, it is perhaps 1" (2.5 cm) long at most. I imagine the coupling mode is a combination of pickup on the power connection, the headphone connection and direct leakage into the enclosure. The driving signal to a diode mixer of the type used in the K2 will be a flat topped as the diodes are driven into conduction during the peak excursions of the LO signal, exactly as you have shown with the oscilloscope photograph you made. Jack K8ZOA Sverre Holm wrote: > Jim, > > >> Does this look OK? >> >> > http://www1.snapfish.com/share/p=55201169346768265/l=239913880/g=15542617/co > brandOid=1000131/otsc=SYE/otsi=SALB > > I think these waveforms are as expected when driving such a nonlinear load > as the diode mixer. > > Also this correlates very well with the reported interference from strong > near-by FM stations in 2002 due to harmonic mixer products, see e.g. > > http://www.ac6rm.net/mailarchive/html/elecraft-list/2002-05/msg00829.html > > There were many reports about this in May 2002, just search for FM in > http://www.ac6rm.net/mailarchive/html/elecraft-list/2002-05/index.html > > and here are some possible explanations: > > http://www.ac6rm.net/mailarchive/html/elecraft-list/2002-05/msg00907.html > http://www.ac6rm.net/mailarchive/html/elecraft-list/2002-06/msg00386.html > http://www.ac6rm.net/mailarchive/html/elecraft-list/2002-06/msg00528.html > > > > 73 > > Sverre > LA3ZA > > Unofficial Guide to K2 Modifications > http://www.qslnet.de/member/la3za/K2/mod.html > > Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Jack, Sverre
Thanks for the feedback. Although the waveform was a bit unexpected since it was of the proper amplitude and fundamental I thought the IC was probably fine. The DC level was also at 4v as expected. The diodes are indeed driven solidly into conduction with the expected flat tops apparent. So it looks like everthing should be fine. Eagerly awaiting the delivery of RFC13. I can't believe that after nearly 50 years of building stuff I cracked the body by not properly bending the leads. I know better than to do that. Bad engineer, no cookie! 73 jim ab3cv _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Jim,
Did you order the KPA100 option? If so, there are 100 uH RF Chokes in that kit that you can borrow until you receive the RFC13 replacement. 73, Don W3FPR > -----Original Message----- > tops apparent. So it looks like everthing should be fine. > > Eagerly awaiting the delivery of RFC13. I can't believe that > after nearly 50 > years of building stuff I cracked the body by not properly bending the > leads. I know better than to do that. Bad engineer, no cookie! > > -- No virus found in this outgoing message. Checked by AVG Free Edition. Version: 7.5.432 / Virus Database: 268.17.0/639 - Release Date: 1/18/2007 6:47 PM _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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Hi Don
No KPA for me at this time. So far I've been satified with QRP. Pam sent them out on Friday so I suspect that they'll be in my mailbox Monday or Tuesday. I finished the initial receiver alignment on the other bands and did the rest of the assy stuff. Then I built up the KNB. Still have the KAF to build today then it will be time to clean out the broken RFC13 in preparation for the new one. I'll probably play around with the Spectrogram program for a while to be ready for final alignment as well. Thanks for the suggestion however! jim ab3cv _______________________________________________ Elecraft mailing list Post to: [hidden email] You must be a subscriber to post to the list. Subscriber Info (Addr. Change, sub, unsub etc.): http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/subscribers.htm Elecraft web page: http://www.elecraft.com |
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