Posted by
dave.wilburn on
Nov 23, 2007; 9:21pm
URL: http://elecraft.85.s1.nabble.com/K2-AGC-Threshold-Too-Low-tp367004p367015.html
Greetings Sarah, welcome to the hobby, and to a great radio. My AGC
measurement was down a bit, not quite as far as yours, but it has been
discussed here that there is some variation, and that it is not critical
at that point. I re-visited my a little later on in the build process,
and the numbers came up some.
Don, W3FPR, has given some good explanations for why this is, I just
don't recall them at the moment. A quick search of the archive;
http://www.mail-archive.com/elecraft@.../maillist.htmlHere is one example of what I found;
http://www.mail-archive.com/elecraft@.../msg01791.htmlSo I don't think your measurement is at a critical level at this time.
Don, or others will likely help with further information. Best of luck
to you, and enjoy the build. It really is a fine radio. 73
-
David Wilburn
[hidden email]
K4DGW
K2 S/N 5982
On Fri, 2007-11-23 at 12:53 -0800, Sarah K. wrote:
> Hi,
>
> I'm Sarah, AF6FH! I just got my license a couple weeks ago, and I'm
> now assembling K2# 0622, which will be my first HF radio. I started
> assembly on Wednesday night, and so far, everything's been going just
> fine.
>
> But...
>
> I'm having a little issue with setting the AGC Threshold.
>
> The instructions (pg. 48) say to set the RF GAIN control fully
> clockwise, measure the voltage on pin 5 of U2 on the control board,
> and adjust trimmer R1 for a reading of 3.80 volts.
>
> I did my voltage measurements with my own (cheap) DMM, not the
> internal voltmeter.
>
> My concern is that, by adjusting R1, the highest I could get the
> voltage to go was 3.59v, so for the moment, that's where it's set.
>
> I measured the voltage on the LM29307-8, and it has 12.23V at the
> input, but only 7.53V at the output. The 78M05 has 4.93V at its
> output.
>
> When I rotate the AF GAIN control, I get a range of 4.68V (fully
> counter-clockwise) to 3.59V (fully clockwise) on pin 5 of U2.
>
> My power supply is a small benchtop power supply; it's putting out
> 12.4V, and reports the K2 is drawing about 100mA. When I measure the
> input voltage across the K2 input jack, I get the same 12.4V.
>
> All of the previous checks were fine, and the following step, S-Meter
> Alignment, seemed to work just fine.
>
> So, my question is, do I have a problem? Should I be concerned?
>
> Thanks,
>
> Sarah AF6FH
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