[Elecraft] Re: K2 AGC Threshold.

[Geoffrey Mackenzie-Kennedy]

Mike,

Great to hear that you are all set and that the work is progressing - and
you are very welcome.

About the problem. Your K2 and mine wanted a higher voltage at U2 pin 5 than
the "normal" to prevent the AGC working on the receiver's own internal
noise. The AGC Threshold was too low and could not be raised because the
adjustment pot R1 had reached the end of its travel. The reason that we
could not get the voltage at U2 pin 5 to the value required for a proper
setting of the AGC threshold was simply that the output voltage from the 8
volt regulator was / is less than 8 volts, but still within the allowed
tolerance, and the divider composed of parts of RP6 along with R1 could not
cater to this lower voltage. Adding the 27K resistor across RP6 (3-4)
compensates enough for the low output from the 8V regulators that we have
and, in my case, results in the wiper of R1 being close to mid-travel when
set for the AGC threshold that I like. But I must stress that this "fix" is
for our K2s. The global modification would have to cater for all DC voltage
tolerances, AGC closed loop tolerances, receiver gain tolerances and so on,
if one goes whole hog - which might not be necessary. But I'll leave those
sums for the lads at Elecraft !

Hope that answers your question, and have fun.

73, Geoff      GM4ESD


----- Original Message ----- 
From: "Mike, W8ENG" <w8eng at arrl.net>
To: "Geoffrey Mackenzie-Kennedy" <gmk at gm4esd.fsworld.co.uk>
Cc: "Elecraft Discussion List" <elecraft at mailman.qth.net>
Sent: Saturday, November 20, 2004 2:11 AM
Subject: Re: K2 AGC Threshold.


> Geoff,   I think I'm all set for now, and the work is progressing nicely.
I
> would be interested in hearing Elecrafts thoughts on the AGC circuit, and
> what you thought the problem was.  Thanks again for the help.
>
> Mike, W8ENG
>
>
>