Proper Adjustment of K2 AGC

[Roy Morris-6]

After reading Don's (W3FPR) AGC procedure, curiosity got the best of me.  I set up my parameters as he stated and was surprised to find a considerable difference between AGC ON and AGC OFF with AGC OFF being considerably louder.  I am going to remove R1 (71K) from the Control Board and substitute a pot to find the proper resistance value.  I understand this pot should be adjusted to where the AGC ON and OFF should be just about the same with the RF gain set fully clockwise.  If I remember correctly a 100K pot should be used to establish the value of R1.  Is this the correct procedure?   Roy Morris  W4WFB
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[Don Wilhelm-3]

Roy,

You must have misread something (or did a typo).  The stock value for
Control Board R1  on the older boards is 51k.  A 50k pot will do the task
for you, or a 20k pot in series with a 33k resistor.  I typically find that
a 39k, 36k or 33k resistor will set the proper level, but I have also found
that the stock 51k value is OK in some cases.  I would hesitate to go below
33k at R1 because as I have mentioned before, the S-meter settings (and
readings) become 'funny' (that is tech-speak for too critical).

I have not yet discovered a concise set of parameters for determining what
the value should be, but I do know that the exact output from the 8 volt
regulator is a large factor - if you have 8.2 volts or more from the
regulator, the stock value is likely correct.  I suspect (but cannot
substantiate nor quantify) that there are minor dfferences in the gain vs.
AGC voltage at the IF amp chip that also come into the picture.

Your procedure is correct, but I would recomend the smaller value for the
pot - the 100k will work, but the adjustment will be more 'touchy' compared
with a smaller value.  Set it to the point where the AGC ON noise is just
barely discernable from the AGC OFF.

73,
Don W3FPR

> -----Original Message-----
>
> After reading Don's (W3FPR) AGC procedure, curiosity got the best
> of me.  I set up my parameters as he stated and was surprised to
> find a considerable difference between AGC ON and AGC OFF with
> AGC OFF being considerably louder.  I am going to remove R1 (71K)
> from the Control Board and substitute a pot to find the proper
> resistance value.  I understand this pot should be adjusted to
> where the AGC ON and OFF should be just about the same with the
> RF gain set fully clockwise.  If I remember correctly a 100K pot
> should be used to establish the value of R1.  Is this the correct
> procedure?   Roy Morris  W4WFB

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[Ron D'Eau Claire-2]

A couple of people have posed a question to me off the reflector that speaks
to a point I think is important: when checking to see if the volume changes
when switching the AGC on and off, do it with *no antenna*! Best, a 50 ohm
dummy load connected!

Background QRN, even up on 10 meters, can easily trigger the AGC, especially
with the preamp turned on. In that case, hearing the audio level increase
when AGC is turned off is normal, indicating normal AGC operation.

Ron AC7AC


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[Roy Morris-6]

----- Original Message -----
From: "Don Wilhelm" <[hidden email]>
To: "Roy Morris" <[hidden email]>; <[hidden email]>
Sent: Monday, August 14, 2006 11:44 PM
Subject: RE: [Elecraft] Proper Adjustment of K2 AGC

Thanks Don.  Yes, I had a senior moment on the resistor value.  I think the
procedure for setting the AGC threshold should be incorporated in the
manual.  This is very important in obtaining optimum performance from the K2
receiver.  Thanks again for your excellent info.  Roy

You must have misread something (or did a typo).  The stock value for
> Control Board R1  on the older boards is 51k.

> Roy,
>
> You must have misread something (or did a typo).  The stock value for
> Control Board R1  on the older boards is 51k.  A 50k pot will do the task
> for you, or a 20k pot in series with a 33k resistor.  I typically find
> that
> a 39k, 36k or 33k resistor will set the proper level, but I have also
> found
> that the stock 51k value is OK in some cases.  I would hesitate to go
> below
> 33k at R1 because as I have mentioned before, the S-meter settings (and
> readings) become 'funny' (that is tech-speak for too critical).
>
> I have not yet discovered a concise set of parameters for determining what
> the value should be, but I do know that the exact output from the 8 volt
> regulator is a large factor - if you have 8.2 volts or more from the
> regulator, the stock value is likely correct.  I suspect (but cannot
> substantiate nor quantify) that there are minor dfferences in the gain vs.
> AGC voltage at the IF amp chip that also come into the picture.
>
> Your procedure is correct, but I would recomend the smaller value for the
> pot - the 100k will work, but the adjustment will be more 'touchy'
> compared
> with a smaller value.  Set it to the point where the AGC ON noise is just
> barely discernable from the AGC OFF.
>
> 73,
> Don W3FPR
>
>
>> -----Original Message-----
>>
>> After reading Don's (W3FPR) AGC procedure, curiosity got the best
>> of me.  I set up my parameters as he stated and was surprised to
>> find a considerable difference between AGC ON and AGC OFF with
>> AGC OFF being considerably louder.  I am going to remove R1 (71K)
>> from the Control Board and substitute a pot to find the proper
>> resistance value.  I understand this pot should be adjusted to
>> where the AGC ON and OFF should be just about the same with the
>> RF gain set fully clockwise.  If I remember correctly a 100K pot
>> should be used to establish the value of R1.  Is this the correct
>> procedure?   Roy Morris  W4WFB
>
>
> --
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> Checked by AVG Free Edition.
> Version: 7.1.405 / Virus Database: 268.10.10/419 - Release Date: 8/15/2006
>
>

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