NARCO Com 11A

[Tom-D]

The wire diagram says to place a 1500 ohm resistor between pin 7&8 if the audio panel is not used.

what does it do?
What will happen if you don't?

Today while I had the 170 out of the hangar I tried the radio, the intercom works on all stations, the radio will transmit but not receive.
Pin 7&8 are both audio pins.
7 = Aux audio in
8 = low level audio out.

 

[weirdjim]

Tom ...

Short answer is that you need the resistor. Anything from 500ð to 2.2Kð should work just fine.

I'll look up the real answer in my 11A manual when I get home this afternoon.

Jim

 

[Tom-D]

Tom ...

Short answer is that you need the resistor. Anything from 500ð to 2.2Kð should work just fine.

I'll look up the real answer in my 11A manual when I get home this afternoon.

Jim

Thanks Jim,

 

[Tom-D]

Fixed it.

 

[weirdjim]

Fixed it.

Good. I got home a little late to do the research, but expect a full explanation as soon as I can get to it.

Jim


.

 

[Tom-D]

Good. I got home a little late to do the research, but expect a full explanation as soon as I can get to it.

Jim


.

No worries Jim, We gotter working. that's all I need. Thanks again.

 

[weirdjim]

Good. I got home a little late to do the research, but expect a full explanation as soon as I can get to it.

That's because NARCO of that era tried the same trick we used in our 502-503 series audio panels, using the aux audio input of the COM transceivers as the power phones and speaker amplifiers of the aircraft audio system.

IF you separate the radio output from the audio system of the radio you can use very simple switching in the audio panel to achieve this goal.

Why the resistor between the pins and not connecting them directly together I can't see from my read of their circuitry other than to try and balance the output between one that has an audio panel and one that does not.

Jim

 

[Tom-D]

That's because NARCO of that era tried the same trick we used in our 502-503 series audio panels, using the aux audio input of the COM transceivers as the power phones and speaker amplifiers of the aircraft audio system.

IF you separate the radio output from the audio system of the radio you can use very simple switching in the audio panel to achieve this goal.

Why the resistor between the pins and not connecting them directly together I can't see from my read of their circuitry other than to try and balance the output between one that has an audio panel and one that does not.

Jim

I simply added the resistor and it worked, I understand that you can use a variable resistor and adjust the volume to the intercom.

 

[bluerooster]

I think the resistor is used to match the impedence of the audio panel when it's not used. Just a WAG.