Thanks to both for info and assistance. You were right Don about the 'weirdness' when injecting signals by C7.
It turns out that the sensitivity issue was caused by a tiny solder bridge on the SMD MC1350 (IF amp) which I found by injecting a signal @ IF freq. before and after the IF Amp. The receiver is now working very nice with an IMD of -136db. The filter/BFO set-up went without a hitch and RX sounds like a million bucks with absolutely no signs of ringing with tight filtering. Are - LB3SA KX1# 1864 K2# 6498 K3: Delivery late July Don Wilhelm wrote: > > Are, > > The 'wierd' symptoms you report could be normal depending on the output > characteristics of your signal generator. The capacitors C7 and C8 in > the 40 meter bandpass form a voltage divider that is intended to match > the high impedance of the filter parallel tuned circuits down to a lower > impedance level. If a signal is arbitrary injected at the top end of C7, > there can (and likely will) be more voltage developed across the filter > than if the same signal voltage is injected at the junction of C7 and C8 > (a similar argument applies to the other bands). Put RFC7 and W6 back > in place to give the proper termination for the filter. > > A valid comparison is to compare the signal at the junction of C7 and C8 > with the signal at the junction of C4 and C5. That would give an > indication of the loss through the bandpass filter. That comparison is > more easily done in transmit than receive (the filter is bi-lateral). > Compare the RF voltage at the junction of D6 and D7 with the RF voltage > at W6 using a transmit power level of 1 to 2 watts. > > If the bandpass filter is not indicating a substantial loss, then you > may have some other problem in the receive path. > > If your bandpass filter does show a substantial loss, try re-peaking it > first, and if that does not produce adequate results, then look for an > impedance mismatch at the filter terminations - check R36 and R5 first > for proper values and good soldering. > > There are many other places other than the bandpass filter that can > cause weak receive. If your K2 develops full output power on all bands, > then the bandpass filter is likely not the problem area. > > 73, > Don W3FPR > -- View this message in context: http://www.nabble.com/K2---signal-loss-in-band-pass-filter-tp17294418p17627350.html Sent from the Elecraft mailing list archive at Nabble.com. _______________________________________________ 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
