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Re: how-to disable agc on ft847/100d



>From: Douglas Cole <n7bfs@qwest.net>
>Anyone know how to do the above ?
>
>Would like to do some noise measurements on my dish/converter setup , but
don't
>know quite yet ( ok , I am lazy and was hoping someone else has done this
>already and can just tell me so I don't have to do the research ;^}  ) how to
>disable the agc on these two rigs .
>
>Tnx for any input !

Sorry, Doug, you can't disable the agc on these and most modern ham rigs.
The manufacturers have determined that hams are too stupid to cope with
manual gain controls, soooo...

That means making Y-factor measurements of noise requires the use of a
precision step attenuator:
1.  Set the system up pointed at cold sky and note the signal level
{preferrably on an accurate audio voltmeter}.
2.  Insert attenuator into coax line ahead of receiver and note the noise
level on the ac meter.
3.  Move your antenna to the sun and peak the noise.
4.  Add attenuation until the meter reads the same as step two.
5.  The sun/cold sky Y-factor = the number of dB added.

Since you bring the noise signal back to the same reference level, the agc
does not affect your measurement.  In fact you should use the slow agc
setting as this smooths the reading somewhat.

Ed

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