Hi Don, Extremely helpful and encouraging; thanks. Actually, I was able to get the trimmers set pretty well, i think, using a strong signal source. But I will make the measurements you recommended. Right now, I suspect either low VFO output or something is pulling down the gain of U1.
Les On Aug 18, 2014 3:00 PM, "Don Wilhelm" <w3...@embarqmail.com> wrote: > Les, > > Yes, the NE612 should show plenty of gain. When it does not, the usual > reason is little or no oscillator signal to pin 6. > > The Pre-mixer Bandpass filter must be aligned before you will get much of > a signal at U1 pin 6. > > Since you have a 'scope (hopefully with a 10X probe), I will give you an > alternate method of tuning the Pre-Mixer Bandpass filter. > > Since you have the 4 band board, you must follow the proper band order - > adjust 15 (or 17) meters before adjusting 20 meters, and likewise adjust 30 > meters before 40 meters. > Make a check before starting - align all the slots in the trimmer > capacitors parallel with the long edge of the band board. Then check the > activity of the crystal for each band - put your probe on band board P1 pin > 4 and not the amplitude of the signal as you switch through the bands - you > should have greater than 200 mV peak to peak. The position of the trimmer > slots when tuned should be no more than 30 degrees from the center position > if your toroids are correct. > > Then switch to 15 (or 17) meters, and with your probe on P1 pin 6, adjust > the Pre-Mixer trimmer caps for 15 meters for the maximum amplitude. Switch > to 30 meters and do the same for that bands trimmers. Do the same for 20 > meters and 40 meters. You should be able to get 200 mV peak to peak there > on all bands. > Remember that your 'scope probe will load the Pre-Mix filter a bit, so the > trimmers to the right of the filter will not be at their optimum setting, > but it will be enough for receive - you will set the optimum position when > you adjust for transmit. > > You should check to see that the Pre-Mix signal is getting to U1 pin 6 - > if it is not, suspect the coax link on the bottom of the board between J9 > and J10. > > Once you have a good signal at U1 pin 6, you should see that the output at > pin 4 is much greater than the input at pin 1. > > 73, > Don W3FPR > > On 8/18/2014 5:20 PM, Les Garwood wrote: > >> Dear Fellows, >> >> I Bought a K1 kit at a ham fest several years ago (SN 02197) and recently >> finished the receiver section. Although audio is strong, as evidenced by >> the hiss, I have nearly no signal on all 4 bands. >> I can pump strong rf into it and hear a good side tone/bfo but not >> strongly. Once, I heard a very faint CW station that was loud on my big >> rig. But no others. >> >From the best of my repeated testings, all voltages and resistances >> provided in the manual match. I have not built an rf probe for my DMM yet >> but will. However, I also used the signal generator kit from Elecraft >> (the KXGI?). It is only weakly audible too, and only on the 50 microvolt >> setting. The AGC setting has no effect. The attenuator kills the weak >> probe signal when on. >> One post I found after scouring the Net spoke of a very similar problem >> that turned out to be a bad 2N7000, in the A Preamp stage, but I can't >> see >> how that would affect signal sensitivity, only audio gain. >> I also put a scope on pin one and pin 4 of U1, the Receiver Mixer. The >> relative voltage was 3x higher on pin 1 than on pin 4. I would at least >> have expected gain instead. >> >> >> > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html Message delivered to arch...@mail-archive.com
