[R-390] Distortion in MGC on strong signal

[eldim at att.net]

Hello Distortion Analyzers,
I find that this seems to be NORMAL BEHAVIOR for any receiver that operates without an AGC circuit, with the audio being distorted in the presence of strong signals.  Thank goodness for AGC, for without it you would always have to fiddle with the RF Gain Control to deal with varying signal levels. I do find the MGC Mode to have it's advantage when trying to pull in very weak signals.  My nickels worth.
73,
Glen Galati, KA7BOJ
Tacoma, WA
42.3 Deg F @ 23:00 Hrs on quiet Wednesday evening


-------------- Original message from "Jim M." <jmiller1706 at cfl.rr.com>: -------------- 


> 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" 
> To: 
> 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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