Posted by
Sarah K. on
Nov 23, 2007; 8:53pm
URL: http://elecraft.85.s1.nabble.com/K2-AGC-Threshold-Too-Low-tp367004.html
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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