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
