[R-390] 1970 US Navy R-390A manual evluation

[Larry H]

Hi Alan,  Thanks for your good questions.  When I reviewed it, I did not
look for those answers, specifically.  So, let me start with what I do know
and get to those a little later.

1. The sensitivity (s/n) measurement is missing a valuable section of
hardware by measuring from the unbalanced input.  At that input, the low
impedance input (balanced), antenna relay, and bandswitch contacts are not
tested.  These 3 items are very important for users that connect coax or a
real balanced line to their rx, which is a very high percentage of
connections.  And they are therefore susceptible to being damaged by
lightning or transmitting.  The only time it is correct to use the
unbalanced input (high impedance) is when it is connected to a whip with a
short coax, or to a random length wire with a very short or no coax, also.
Connecting a coax to the unbalanced input longer than 15 or 20 feet applies
too much capacitance to the circuit.  This impairs the 'Q' of the circuit
and seriously impairs its filtering effect.  The TM-11-856A gets it right.
But, on the other hand, the 1970 Navy manual procedure does a very good
thing and uses the line level meter for part of the measuring
procedure instead of an external meter.  This is a good improvement.

2. There is no procedure for adjusting or testing the balanced antenna
input ratio adjustment, The TM-11-856A has it.  But, this does not need to
be done unless you are using a balanced line input.

3.  The carrier level meter test says to set the sig gen output for 20 db
and increase its output in 20 db steps until you get to 100 db  (some of us
may know that this is equal to a 10x increase in signal strength each step,
but some may not).  Each step should be within +/- 2 db, or repair is
needed.  Most sig gens only measure in uv.  The doc should make a note of
the 10x relation.  Because the db unit is a relative measurement, it should
say what it's based on, but it does not.  Further, it should state that
it's based on 1uv and that each 20 db increment is 10x the previous, so the
sig gen increase should be 10uv, 100uv, 1,000uv, 10,000uv and finally
100,000uv for 100 db, but it does not say that.  The TM-11-856A does.

I haven't had time to go into more details, but will when I have time.

Regards, Larry

On Sun, Oct 17, 2021 at 5:05 AM Alan Victor <amvictor at ncsu.edu> wrote:

> Hi Larry,
>
> Are there unique aspects to this Navy Manual not found in the Army or any
> other type manual?
> Are there improvements in techniques for troubleshooting and repair?
>
> 73' Alan
> W4AMV
>