[R-390] Distortion Troubleshooting

[Bill Cotter]

Thanks, Bill -

Even though the IFG was set during final alignment, I will try to 
set it the 'Navy Way' with the sig gen input.

I am pleased to learn 150uV is the setting range, that makes the 
operating range likely to be closely above and below this number. 
Your reasoning about the stage-gain in the RF section would 
substantiate this idea. I will go about setting the IFG in this 
manner, and testing afterwards should lead towards either the IF 
deck or RF deck as the source.

73 bill n4alg


At 04:41 PM 3/10/2002, you wrote:
>Hope you are getting some good suggestions, but in case we're
>all waiting for someone else to step in, I'll make a basic
>suggestion:
>
>Have you set the IF Gain pot on the IF Amp Assy? The Navy
>manual says to change the RF cabling so that the IF Out jack
>is connected to IF In on the IF Amp. Supply 150 microvolts
>at 455 KC, 30% mod to the external IF Out jack. Set Function to
>MGC and RF Gain to 10. Adjust IF Gain for -7 VDC at the Diode
>Load terminal, not the AGC voltage. See the Manual for further
>details.
>
>Since the RF Deck has only one stage of gain (the other tubes
>are oscillators and mixers) it seems unlikely that the IF Amp
>would see as much as 10 millivolts input, but I don't know the
>design input range. Perhaps the Technical Report has it.
>
>Usually, distortion comes from clipping, which can be from core
>saturation. In the 390A, it can also come from overdriving
>the mechanical filters.
>
>Does anyone know the design input range for the IF Amp?
>
>Regards,
>Bill Hawkins