Hi I don't know if I can help but here are a few thoughts. First the S-meter is just an indication of the AGC voltage so it is normal for it to not work when the AGC is turned off because there is no AGC voltage when turned off.
If you are losing the signal out of the crystal filter check each crystal pin to ground with an ohm meter. You should get a high reading not a short. Sometimes if too much solder is used the solder will flow up under the crystal shorting it to the ground plain on the top of the board under the crystal. If one of them is shorted you will need to remove that crystal and remove the excess solder. The RF probe outputs a DC voltage to your meter but the component values on the probe and the 10 meg ohm input resistance of the meter form a divider that makes the DC voltage read on the meter equivalent to the RF RMS voltage at the probe tip. Don Brown KD5NDB ----- Original Message ----- From: "Chris Kantarjiev" <[EMAIL PROTECTED]> To: <elecraft@mailman.qth.net> Sent: Tuesday, February 28, 2006 11:43 PM Subject: [Elecraft] low audio on K2 s/n 3641 (was RE: PLL ReferenceOscillator Range Test) > Last night I sent out a message about my PLL reference oscillator range > test showing the range to be a bit too small; I was starting to track > down the low-audio on new-to-me s/n 3641. > > Don W3FPR made several helpful suggestions off-list, none of which > panned out (including checking T7). I played around with the AGC > settings and discovered that there is reasonable (but not room-filling) > audio when the AGC is off, but turning on the AGC quiets it way > down. I also found that the S-meter response is not what I expect: > > I injected a -50dBm signal at 7100KHz. I zero-beat it with SPOT on. RF > gain is fully clockwise. > > - I really don't understand what the S-meter is meant to do when switching > AGC off and on: it seems that when the AGC is on, the S-meter reading goes > up even if the audio goes down; when I switch the AGC off, the S-meter > reading droops off the left edge. What's going on here? > > - I expect this to be S9 or so, and it's much less. I have done CAL S LO > and CAL S HI several times, just to be sure. When I drop the signal to > -100dBm, the S-meter is zero; it takes about -70dBm to get the meter > to register. > > I found a note from Gary Surrency of Elecraft in the archives, "K2: 25 > reasons for low RX sensitivity or low audio. (long)". The first > things he mentions is checking CAL FIL. So I borrowed Leigh WA5ZNU's > ngen and used Spectrogram to set the filters per Tom N0SS's > excellent instructions. (Some day I'll understand why everyone > chooses different filter widths :-) > > So I started on the Receiver Signal Tracing in my manual. Everything > was more or less correct until I got to the crystal filter: > > 4. Post-Mixer Amp Output. Expected 2.2Vrms. Got 3.02Vrms > > 5. -5dB Pad Output. Expected 1.40Vrms. Got 3.04Vrms > > 6. Crystal Filter Output. Expected 0.35Vrms. Actual 0.094Vrms. > > I stopped there, because this seems very wrong. > > In Gary's note, he mentions that the crystals here should be marked > 4915-20, not 4915-S. Mine are marked 4.9136-S, which is what the > manual's inventory lists for the crystal filter set... > > So. I'm open to suggestions. Thanks! > > 73 de chris K6DBG > > P.S. Should these readings really be listed Vrms? It's a DC voltage > after it leaves the RF probe, isn't it? I'm certainly reading it > on my DC scale. > > _______________________________________________ > 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 > _______________________________________________ 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
