Burt, I am interested by that mod also.
Thanks in advance, Didier KO4BB Sent from my Verizon Wireless BlackBerry -----Original Message----- From: "Burt I. Weiner" <b...@att.net> Sender: time-nuts-boun...@febo.com Date: Thu, 24 Feb 2011 13:12:25 To: <time-nuts@febo.com> Reply-To: Discussion of precise time and frequency measurement <time-nuts@febo.com> Subject: [time-nuts] To Bert from Burt... Bert, I run my 3586B from an external GPS controlled reference. There's no practical relationship for the product detector L.O. that would be easy or likely worth the effort. Here's a link to my FMT Methodology that describes what I've done. If you're interested in the I.F. pickoff point information let me know and I can e-mail to you information on "How I Did It". See: http://www.k5cm.com/k6OQK%20FMT%20NEW.htm Burt, K6OQK >Hi Everyone, > >Some recent tests I have made on my HP 3586B Selective Level Meter have >confirmed that the detected audio drifts a lot as a function of ambient >temperature. A day/night change of 1.5 degree Celcius was clearly visible on >Spectrum Lab samples. I could actually find out how many times and when the >central home furnace had cycled in-out overnight. It gave a neat plot which I >post here: https://www.onlinefilefolder.com/3sFcUl8Z8i8zy7 > >So I have been looking at modifying my HP 3586B SLM so that it >becomes entirely >synchronized off the external 10MHz reference. As you probably know, >all stages >exept the final one, the SSB LO (BFO), are derived from the 10MHz reference. >The SSB LO chain is made of two free-running crystals used for LSB and USB >detection. In my unit (3586B, option 003), the detection LO frequencies are >13775 Hz and 17475 Hz. These two frequencies are not directly math-related to >any other internal reference (at least I could not personally find any). BTW, >the IF LO rate is 15625 Hz. > >I have substituted a function generator instead of the internal >oscillators just >to see how much the off-centering would affect the audio quality, >and found out >that this works well as long as it is not too far off the designed >LO rates. The >closest 10MHz-derived integer rate I could find that will work for audio tone >measurement is divide-by-726 (13774.104... Hz) in LSB. The closest USB rate >would be divide-by-572 (17482.5... Hz), much farther than the LSB one. So the >LSB rate difference of around 0.9 Hz can be neglected when keying in the >frequency and listening to regular radio signals. When making absolute audio >measurements, subtracting that delta is easy to achieve in post processing. >Besides, the frequency and amplitude measurement capabilities of the >instrument >are not altered by this mod. To me this would seem like an >acceptable compromise >that is simple to implement and would add long-term stability. My >intent is to >have a single chip (in this case, an 8-pin PIC divider) do the >trick, as we are >dealing with tTL level signals here. > >But can I do better? >How much more complex? >Can I avoid PLLs? >All mixer stages become synchronized to a single source. Is this an issue for >reliable audio detection? >Am I missing something here? > >As always, I truly enjoy your feedback and am quite convinced I will learn >something new once more. > >Thanks, > >Bert, VE2ZAZ > > > > > Burt I. Weiner Associates Broadcast Technical Services Glendale, California U.S.A. b...@att.net www.biwa.cc K6OQK _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.