[R-390] R390A GAIN ADJ and final testing

[Bob Camp]

Hi

Since the manuals were written there have been some changes in how we 
do things in these areas.

The input to the radio at the antenna jack should be the same impedance 
as the antenna you will use. If you use a 50 ohm antenna then use a 50 
ohm generator. The dummy load mentioned in the manual is only required 
to convert a 50 ohm generator into a 120 ohm generator. Since we do not 
have very many 120 ohm antennas we rarely use the dummy load.

The IF gain setting in the manual was intended for running multiple 
radios in a diversity system. Some of these systems used the AGC 
voltage as part of the "voting" between the receivers.

Today thanks to members of this list we think that there is a better 
way to adjust the IF gain. We set it to optimize the sensitivity of the 
radio. This is a lower gain setting than the military recommended in 
the manual. Because it is a lower gain setting it also improves the 
overload performance of the radio.

The web site www.r390a.com has some good information on both of these 
points if you are looking for more information.

	Enjoy!

		Bob Camp
		KB8TQ




On Jul 18, 2004, at 6:39 AM, Francesco Sartorello wrote:

> Hello, everybody!
> in accordance with TM 11-856A, para 148 (adjustment of GAIN ADJ
> Potentiometer R519) signal generator should be connected to J513 v ia 
> an
> MX-1487 Impedance Adapter: is this a simple 50 ohm termination for the
> Signal Generator as the CU-406/URM-25F or else?
> About overall sensitivity, I have the impression that approximately 
> the same
> results can be achieved with both antenna inputs (Balanced and 
> Unbalanced),
> with proper setting of the Antenna Trimmer and alignment of the first 
> set of
> RF coils is not so dependant from the antenna input used: will someone
> comment on this?
> What about Electrcal Dummy Load DA-121/U mentioned in Section 5- Final
> Testing? Is it, maybe, something like a DA-109/URM-25F with a resistive
> partitor to obtain balanced output?
> Ciao a tutti!   FSarto
>
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