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Re: IC-910 AGC

At 07:54 PM 2/16/2003 +0000, f6bki wrote:
>I would like to use my IC910H to make some sun noise measurements to compare
>antennas /preamps etc.... The problem is that it is not possible to switch
>off the AGC on this rig . Is there people that have made modifications ? any
>other ideas ??
>Thanks 73
>Jacques F6BKI


This is a common problem with modern ham rigs.  One way of making sun-noise
measurements without defeating the agc iby using a precision step
attenuator.  First you point at cold sky and measure your audio output with
a good AF voltmeter.  The peak on the sun and add attenuation unitl the
voltmeter reads the same as cold sky.  The solar noise value is the amount
of attenuation you used.  This is not very accurate with small AO-40 dishes
since they may only show 1-2 dB of noise rise.

Others have maintained that agc is not that significant with the slight
shift in level involved, so you might calibrate your receiver with a signal
generator and note the level change on the generator for the two levels.

Ed - AL7EB
I have seen about one-half s-unit noise rise looking at the sun with my
85cm dish.  This is ~2 or 3 dB (verified with a precise audio voltmeter
made by Sinader). 

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