-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 Don Wilhelm wrote: > Ron, > > The problem is that your crystals have a Q which is high and they are > more difficult than the average to pull down in frequency. > > Your best recourse is to pad the crystals down in frequency a bit. You > can first try a small capacitor from the junction of the crystals and > C174 (U11 pin 6) to ground. My rule is that the capacitor should not > exceed 20 pf. Too much capacity here can cause the BFO oscillation to > act 'strangely'. > > If 20 pf will not lower the low frequency enough, then add a padder > capacitor to both C174 and C173. 47 pf across C174 and 120 pf across > C173 should do the job nicely and preserve the ratio of the two > capacitors - the ratio is important to control the feedback for the > oscillator circuit. > > 73, > Don W3FPR >
Don, Updated data below. No real progress with the padding. :-( A B 10pf 20pf 47/122pf BFO Hi 4917.62 4917.63 4917.11 4916.8 4917.39 BFO Lo 4913.59 4913.49 4913.3 4913.16 4913.02 Range 4.03 4.14 3.81 3.64 4.37 A is the original set of BFO crystals B is the replacement set of crystals Try 1: 10pf from pin 3 - 6 of U11 Try 2: 20pf from pin 3 - 6 of U11 Try 3: 47pf across C174, 122pf across C173 As you can see by the data padding the junction of the crystals only reduced the upper range. So I then tried the recommended padding across C173 and C174, and, as you can see, it still fails to bring the lower range into spec. Where to go from here? Thanks a mil for all the help. Ron - -- - -=-------------------------o---------------------------=- Ron Hahn, EI2JP | Grid Square: IO62TG Rose Hill | Fists: 10883 Rosslare Strand | QRP-ARCI: 12584 County Wexford, IRELAND | K2: 4922 __+__ -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.7 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFGgP4xyJCeYjZnfkQRAkf1AKCLMNWQAeDCdE2qq73TEWwRa9q7PACgpL21 k4Vjs2ml++Lh7AktxnYuDyw= =Elee -----END PGP SIGNATURE----- -- This message has been scanned for viruses and dangerous content by MailScanner, and is believed to be clean. _______________________________________________ Elecraft mailing list Post to: Elecraft@mailman.qth.net 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