[R-390] Distortion in MGC on strong signal

[Jim M.]

My radio is also driven into distortion in MGC unless I back off the front 
panel RF gain.  What you describe seems to be normal behavior on strong 
signals.  Things work much better with AGC on, that's why there is an AGC 
circuit.  In fact I leave my AGC on all the time.


----- Original Message ----- 
From: "Barry" <n4buq at knology.net>
To: <r-390 at mailman.qth.net>
Sent: Wednesday, March 14, 2007 11:50 PM
Subject: [R-390] Distortion in MGC on strong signal


> When tuned to strong stations in MGC mode, my R390A is driven into
> distortion.  Monitoring the Diode Load, I'm seeing approximately -60V when
> tuned to a strong station.  Backing the RF Gain control to where the Diode
> Load reads more around -30V causes the signal to sound normal again.
> Switching to AGC (any AGC speed) causes the Diode Load to drop to 
> about -30V
> and the signal sounds normal as well.
>
> I can reduce the IF Gain to almost zero and cause the Diode Load in MGC 
> mode
> to be around -30V with the RF Gain at "10", but I'm sure this is too low 
> of
> a setting for the IF Gain Control.  I've followed the manual's procedure
> (150mV into the IF deck and set for -7V Diode Load) as well as backing it
> off slightly for Chuck Rippel's procedure so setting it far enough back to
> keep the Diode Load down to an acceptable level when the RF Gain is at 
> "10"
> is not the correct solution.
>
> I assume the radio should not be acting this way, right?  If not, any
> suggestions on where to look for problems?
>
> Thanks,
>
> Barry - N4BUQ
>
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