[R-390] EAC R390A question

[Bob Camp]

Hi

The magic unlabeled jack normally is connected to the diode load test 
point on the rear panel. It is a standard military installed 
modification and not something dreamed up by the previous owner of your 
radio. The workmanship on the mod varies since it apparently was only 
done as a field mod.

Previous posts have referred to this as the "navy diode mod". Once the 
radio was mounted in a rack getting to the back panel on a typical Navy 
install was not a real easy thing to do. I have no direct experience 
with the system, but there are Navy antenna multicouplers that are 
tuned to match the radio. Having a signal level to do this with 
probably was a helpful thing. I also suspect it was a pretty good way 
to check a radio before pulling it for repair.

By far the most interesting (to me at least) use of the diode load 
point is in direction finding. With a good voltmeter and a little 
calibration table you can read out signal levels to a amazing level of 
accuracy. All of the applications I have heard of have been airborne, 
but the Navy may have been doing the same thing.

	Enjoy!

		Bob Camp
		KB8TQ


On Feb 25, 2005, at 8:33 AM, jonklinkhamer at comcast.net wrote:

> Hello Folks,
>
> I'm going thru the process of restoring a 67 EAC 390A model and was 
> looking for some information on a test point near the phone plug on 
> the front panel. The test point is a green plastic post that does not 
> have any wiring on it behind the panel. Although I think it did at one 
> point since there is evidence of soldering. My reading of various 
> postings and literature seems to indicate that it was for the diode 
> load. Most likely the test point is more convenient in the front then 
> back. It just seems out of place. There is no labeling above to 
> indicate such feature and I don’t see a lot of radios with this. Can 
> anybody shed some light?  PS: I very much enjoy this group. You guys 
> are obviously very talented bunch.
>
> Thanks,
> Jon, KB1DC
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