[Milsurplus] [MMRCG] GRC-106 AME problem

[Meir Ben-Dror WF2U]

Thanks Ray,

 

Yes, I’m aware that the AM is AME – single sideband with full carrier insertion. I have the manual in front of me and I studied the steps to set the APP/APC and the  AM carrier level. The module carrier output on AM should be half the voltage of the peak output with tone input on SSB – 15 mV as opposed to 30 mV on SSB with the specified tone input level in the manual. I got the long amplifier control cable for working on the exciter away from the rack, to see how the AM mode works with the amplifier, before buttoning up the exciter. Instead of a millivoltmeter which I don’t have, I’m going to use a scope.

 

73, Meir WF2U

Landrum, SC

 

From: Ray Fantini 
Sent: Monday, January 4, 2021 2:37 PM
To: Meir Ben-Dror WF2U <wf2u at ws19ops.com>
Cc: mmrcg at groups.io; MRCA <mrca at mailman.qth.net>; Milsurplus <milsurplus at mailman.qth.net>
Subject: RE: [MMRCG] GRC-106 AME problem

 

Remember that the GRC-106 has no AM, they make a fake AM by running USB and also injecting a carrier thru R14 on 1A5 

Power control is by the PPC and APC voltages. A1R15 controls overall PPC voltage and is derived from the amplifier. It works with A1R14 the ALC level by the fixed resistor network on the mode control. The other adjustment under the cover is A1R13 that sets the power level in the TUNE mode.

If the exciter is overdriving the amplifier and is causing plate trips it would be interesting to see what the PPC and more important the APC voltages are doing. You can see the test points for each on top of 1A5

PPC is more audio derived and used to control distortion, APC is derived from the 1A1A2A5 located under the chassis from what I recall and derived from the exciter output.

Try to avoid the temptation to just crank on R14 on 1A5 (AM Carrier Level) because if the PPC and APC are not working that can result in the radio always running wide open.

Think the manual refers to both voltages being around 3 volts under normal operation but would not swear to that.

 

 

Ray F/KA3EKH

 

 

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