[R-390] service of an R-725

[Les Locklear]

There is another excellent article in ER #200 written by my late friend Chuck Teeters telling the R-725 story.

Les Locklear


----- Original Message -----
From: Nick England <navy.radio at gmail.com>
To: <wb3fau55 at neo.rr.com>
Cc: R-390 HF Receiver List <r-390 at mailman.qth.net>
Sent: 12/6/2016 7:49:44 AM
Subject: Re: [R-390] service of an R-725
________________________________
An article by Tom Marcotte in ER #84 covers the R-725 background and its
use in the AN/TRD-15 DF system. I am not familiar with the TRD-15 but this
seems a little odd to me as a wideband Wullenweber system such as AN/FRD-10
or AN//FLR-9 depends on phase accuracy to the goniometer which combines RF
signals - all this happens well before the receivers - which were often
R-390A (or R-1230/FLR)

I have also read two other theories -
a) The R-725 was intended for ELINT use, where the IF output was recorded
onto a wideband recorder for later analysis while retaining the best
phase/amplitude fidelity. This theory says the DF use was mainly a red
herring. The R-1511/GR and R-1230/FLR were widely used in this manner, with
banks of them feeding wideband recorders. This also seems a little odd to
me as you hear plenty about the R-390A and SP-600 in ELINT use, and the
wideband recording systems depend on wide IF output like from the R-1230
and R-1511.

b) The R-725 was used in a spread spectrum secure RTTY system called F9C
which depended upon multiple receivers good phase linearity through the
passband. This theory also says the DF use was mainly a red herring. This
one makes some sense to me. Google "R-725" and F9C. There is an interesting
article named "The NOMAC and Rake Systems".

Pick a theory, any theory,,,,


Nick England K4NYW
www.navy-radio.com<http://www.navy-radio.com/>

On Mon, Dec 5, 2016 at 7:07 PM, <wb3fau55 at neo.rr.com> wrote:

> 390A gurus- a number of questions concerning the R-725. So straighten me
> on a number of points with this item. A 725 is a modified 390A, not
> using mech. filters, for whatever reason?
> I may get one of these for repair. The problem- no receive below 8mc.
> Fairly common problem in the 390A, in the 1st xtal osc. So my main
> question is- any difference in the RF deck of a 725 vs. a 390A?
> As always, thanks for your input-73s Russ.
> ____________________________________________________________
>
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