AGC Threshold voltage?

[nz8j]

The overall receiver gain  of the K2 I just built (serial number 4993) seems
low as compared with my older serial number 315 K2.

The max AGC threshold voltage I can get is 3.82 volts. (3.8 is what is
called for in alignment and Test Part I), but the troubleshooting section
says you can increase the voltage to increase the overall no-signal IF gain
and that a typical setting might be 3.9 volts.  Mine is maxed out at 3.8...
does this sound correct?

Thanks
Tim
Nz8J


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[Evert Bakker (PA2KW)]

Hello Tim,

I had the same experience. Mine was max 3.78V but it seems nothing to worry
about. I do agree that the given figures and the real ones don't give the
right feeling. I was worried as well. It would haven been "better" to have
the real figures somewhere midway the lower and maximum limits to give a
proper feeling of being normal.

Evert, PA2KW
K2 #4836

-----Original Message-----
From: [hidden email]
[mailto:[hidden email]] On Behalf Of NZ8J
Sent: 25 July 2005 18:58
To: [hidden email]
Subject: [Elecraft] AGC Threshold voltage?

The overall receiver gain  of the K2 I just built (serial number 4993) seems
low as compared with my older serial number 315 K2.

The max AGC threshold voltage I can get is 3.82 volts. (3.8 is what is
called for in alignment and Test Part I), but the troubleshooting section
says you can increase the voltage to increase the overall no-signal IF gain
and that a typical setting might be 3.9 volts.  Mine is maxed out at 3.8...
does this sound correct?

Thanks
Tim
Nz8J


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[Don Wilhelm-3]

Tim,

Actually that troubleshooting section of the manual is incorrect - the gain
of the receiver will increase if you DECREASE the AGC THRESHOLD voltage.
The really optimized voltage for the AGC Threshold is the highest voltage
that shows no change in internal noise (no antenna connected) when changing
from AGC On to AGC Off (press AGC and PRE/ATT buttons together to toggle AGC
on/off).

I normally find that a setting in the range of 3.7 to 3.8 volts will be the
optimum point, but it will vary from K2 to K2.

Try monitoring the voltage at Control Board U2 pin 5 to convince yourself
that a lower voltage will result in higher gain.

The max voltage that one can find at U2 pin 5 will be determined by the
actual voltage on the 8A line - it will be a bit less than half that
voltage - and is not really an indication of any problem.  The 8A voltage
can vary from 7.6 volts to 8.4 volts and the regulator will still be in spec
(and OK for use in the K2).

73,
Don W3FPR

> -----Original Message-----

>
> The overall receiver gain  of the K2 I just built (serial number
> 4993) seems
> low as compared with my older serial number 315 K2.
>
> The max AGC threshold voltage I can get is 3.82 volts. (3.8 is what is
> called for in alignment and Test Part I), but the troubleshooting section
> says you can increase the voltage to increase the overall
> no-signal IF gain
> and that a typical setting might be 3.9 volts.  Mine is maxed out
> at 3.8...
> does this sound correct?
>
> Thanks
> Tim
> Nz8J
>

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[Larry Makoski W2LJ]

The max on K2 #4090 was 3.78V, too.  I moved on and didn't worry about
it.  The radio works great!  If it was more than .5V difference, I
probably would have been more concerned.

73 de Larry W2LJ

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[nz8j]

Thanks to everyone for the suggestions and help... As Don pointed out the IF
gain decreases with an increase in voltage.  I set the voltage at a point
where there is no difference in the background noise with AGC on and off and
the sensitivity is better....I built the little Elecraft generator a few
minutes ago that I had been putting off for months.... :)  The new K2 shows
SO-9 in the 50 micro position and the old one does too...  AGC threshold
voltage is only 3.30v now though, but everything seems to be working fine...
I guess that won't be a problem..
thanks again
Tim
Nz8J
----- Original Message -----
From: "NZ8J" <[hidden email]>
To: <[hidden email]>
Sent: Monday, July 25, 2005 12:57 PM
Subject: [Elecraft] AGC Threshold voltage?


> The overall receiver gain  of the K2 I just built (serial number 4993)
seems
> low as compared with my older serial number 315 K2.
>
> The max AGC threshold voltage I can get is 3.82 volts. (3.8 is what is
> called for in alignment and Test Part I), but the troubleshooting section
> says you can increase the voltage to increase the overall no-signal IF
gain
> and that a typical setting might be 3.9 volts.  Mine is maxed out at
3.8...

> does this sound correct?
>
> Thanks
> Tim
> Nz8J
>
>
> _______________________________________________
> Elecraft mailing list
> Post to: [hidden email]
> You must be a subscriber to post to the list.
> Subscriber Info (Addr. Change, sub, unsub etc.):
>  http://mailman.qth.net/mailman/listinfo/elecraft
>
> Help: http://mailman.qth.net/subscribers.htm
> Elecraft web page: http://www.elecraft.com
>

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