Hi Don and All I have used this method on 3 or 4 of the K2's I have built. I use a 1pF or 2pF NPO cap to lower the bottom end of the range to get it to meet the spec. I agree with you on pulling the crystal much with this method. I would not recommend cap values above maybe 3 or 4 pF. I have never needed more than 1 pf. Padding C173 and C174 is a better method if the radio needs more than 1 or 2 pf. I believe this method was suggested by Gary at Elecraft some time back. At any rate it is a little easier to do than the padding or change out of C174 and C173
The other Don Don Brown KD5NDB ----- Original Message ----- From: "Don Wilhelm" <[EMAIL PROTECTED]> To: <[EMAIL PROTECTED]>; <[EMAIL PROTECTED]>; <[email protected]> Sent: Thursday, December 08, 2005 5:03 PM Subject: RE: RE: [Elecraft] K2 BFO Test > Sverre, > > I have not tried that small capacitor from the junction of the crystals > and > L33 so I cannot comment on it from that standpoint. > > What I would like to state is that when one pulls a crystal by any method, > the stability becomes worse as the amount of pulling becomes greater. One > should be aware of this and related facts when modifying any circuit in a > way that is not 'approved and tested'. Also due to the nature of > crystals, > something that happens to work in one situation may not work the same for > all cases. Remember that I am only bringing up cautions here, I am not > makeing a firm statement about the operation one way or another. > > It certainly would be nice if someone (or better yet, several someones) > with > access to suitable instrumentation could try this or any other mod and > report the results. The fact that it worked on a sample of one does not > create a statement that it will work in other cases - that is simple > statistical knowledge - I would like to see something that says it works > in > at least 5 or 10 trials before drawing any firm conclusions. > > So, yes I think it should be left on your website, but you may want to put > a > "Use at your own peril" disclaimer on all those that are not 'approved by > Elecraft' or otherwise adequately tested (and I invite you to add any of > my > mods to that group as well, even though I have absolute confidence in my > own > work). > > 73, > Don W3FPR > > > -----Original Message----- > > > > > > The preferred method of padding the BFO capacitors is to > > > maintain the ratio between C173 and C174 by paralleling them > > > with capacitors. A single capacitor from the junction to > > > ground will be in parallel with the series combination of > > > C173 and the varactor D38 and could make the BFO less stable > > > than it should be. > > > > > > > Don, > > > > How about a single capacitor (1-4 pF) from the junction of the > > crystals and > > the L33 inductor as in > > http://www.ac6rm.net/mailarchive/html/elecraft-list/2005-08/msg00562.html? > > Does that create potential stability problems also? > > > > I've got this link on my K2 mods page and just wanted to make sure I can > > recommend it and keep it there. I have never had any problems > > with BFO range > > myself so I have no personal experience with this myself. > > > > 73 > > > > Sverre > > LA3ZA > > http://www.qslnet.de/la3za/ > > > > _______________________________________________ > Elecraft mailing list > Post to: [email protected] > 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 > _______________________________________________ Elecraft mailing list Post to: [email protected] 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
