[R-390] TRD-15, Was The R-725 and the DF story?

[wjneill@lcc.net]

TM 11-5825-231-10 covers AN/TRD-15 AND AN/TRD-23=2E  The R-725 is=20
mentioned only as a component of both sets and there are no=20
instructions for operation or maintenance=2E  In other words, there is no=20=

stand-alone TM for the R-725 nor are there higher level maintenance=20
manuals for the AN/TRD-15 or AN/TRD-23=2E

Bill Neill
Conroe, Texas

Original Message:
-----------------
From: Tom M=2E courir26@yahoo=2Ecom
Date: Mon, 8 Dec 2003 05:12:07 -0800 (PST)
To: tetrode@comcast=2Enet, r-390@mailman=2Eqth=2Enet
Subject: [R-390] TRD-15, Was The R-725 and the DF story?

John and group,

The DF set used with the R-725 was the TRD-15 (and one other that=20
escapes me at
the moment)=2E

The R-725 was prototyped by Motorola, and then the rigs were=20
modified by Arvin
and Servo=2E

Arvin and Servo took existing 390A depot dogs, removed the IF decks=20
and
salvaged certain parts (such as the BFO, crystal filter and a few others)=20=

and
built up new IF decks called "SERIES 500" decks to drop in=2E  They also=20=

added a
transformer to use for hum-bucking on the PTO=2E

Important:  The SERIES 500 deck and the R-390 deck are not=20
interchangeable=2E=20
The filament voltages and IF hookups are different, but mechanically=20
they are
95% the same=2E

I'm told the reason the R-725 was sold for DF purposes and not the R-
390 was
that Collins and the Signal Corps jumped into the R-390A with both=20
feet=2E  The
use of the R-725 over the R-390 was a face saving measure to stay=20
within the
R-390A concept=2E  This was probably also justified by training,=20
documentation
and parts drivers as well=2E  The Army cut the cord on the R-390 and=20
didn't go
back=2E

Servo is still in the DF business=2E

see:

http://www=2Eservo=2Ecom/

 =20

73 Tom N5OFF
--- John KA1XC <tetrode@comcast=2Enet> wrote:
> Since we're on the subject, I'd like to bring up a question that's been=20=

on
> my mind about the reported purpose of the R-725 and its DF friendly=20
IF deck=2E
> Is DF use really the case, or is this just a story that gets repeated?
>=20
> While I've often read this explanation, I've never seen any
> documentation referring to what actual DF equipment or systems the
> R-725 was used with=2E I'm very familiar with the need for carefully
> characterizing the IF phase or group delay characteristics for=20
particular
> applications, but I am unfamiliar with any needs for DF=2E Maybe I don't=

> understand this requirement but could there be another explanation?=20
The
> following is my reasoning=2E
>=20
> DFing to me means determining the location of an emitter
> From what I know about the major HF DF systems used (such as the=20
giant
> Wullenwebber arrays that were deployed world-wide) they could be=20
simplified
> into three parts:
>=20
> i) the antenna array which is used to receive and resolve the emitter
> bearing
> ii) the receiver which allows you to listen in and provides a=20
conditioned
> IF output
> iii) the display processing equipment which takes the IF signal and=20
extracts
> the amplitude information and puts it in a form which can be used to=20
create
> a rotating polar display=2E This gives you the familiar DF scope with th=
e
> propeller shaped display indicating bearing=2E
>=20
> The whole point of this is that it is the emitters amplitude which is=20=

being
> plotted against bearing, and I just don't see the emitters phase=20
components,
> or the IF's, coming into the equation=2E I've also heard stories told by=
 DF
> and intercept operators of such centers being filled with racks and=20
racks of
> R-390's, R-390A's, and R-391's, but don't recall R-725's being=20
mentioned
> much if at all=2E
>=20
> Perhaps I'm missing something in the above explanation, but I DO=20
have some
> applications in mind where linear IF phase would be handy=2E
>=20
> 1) Radio-location, defined as determining where the *receiver* is=20
located
> based on known transmitters=2E
>=20
> The transmitted signals contain precisely timed pulse information=20
which can
> be translated to distance, so having an IF that preserves the phase=20
(and
> therefore the timing) of the pulses is important=2E But there was lots o=
f
> specialized radiolocation receiving equipment built and sold;  why=20
would you
> use an R-725 (plus other equipment), and why buy an expensive=20
receiver that
> covers all of HF when radiolocation utilizes lower frequency ground
> wave?  This doesn't make much sense to me=2E
>=20
> 2) Data communication, involving something more complex than the=20
usual
> multi-channel TTY, but have not seen any references to this=2E
>=20
> 3) ELINT, Electronic Intelligence gathering, a big time Cold War=20
activity=2E
> This is where you are interested in the actual  RF signal itself so that=
=20
it
> could be analyzed and information extracted, or so that it's "signature"=

> could be determined=2E
>=20
> Back when the NSA was formed, they (and their various agencies)=20
started
> analyzing all the foreign signals they could from DC to light, and=20
continue
> to do so today=2E
>=20
> Wide-bandwidth analog recorders had arrived on the
> scene and remote listening posts, planes, subs, and ships hugging=20
other
> countries borders were filled with all kinds of receiving gear quietly
> listening in and feeding these wideband recorders signals straight=20
from
> their IF outputs=2E
>=20
> Miles of tapes were routinely recorded every day, then rushed to
> centralized analysis labs for study=2E That is one of the main reasons
> surveillance receivers have IF signal outputs=2E
>=20
> This is one application where keeping all of  an unknown signal's=20
amplitude
> and phase components intact would be the highest priority, since the=20
goal
> would be to record the desired signal in its original form with the=20
minimum
> distortion possible=2E
>=20
> For this special purpose the R-725 would fit the
> bill, the few hundred built could have been all that was needed=2E=20
ELINT was
> routine on VHF up through the microwaves, so why not HF too?
>=20
> Could HF ELINT have been the real purpose for this radio? The DF=20
story might
> be just that, a very believable cover story used to explain the=20
procurement
> contract, brought to you by the cloak and dagger folks that
> like to keep their real business quiet=2E
>=20
> Perhaps I've just been typing into the wind, but just maybe there is=20
someone
> reading who could chime in and perhaps shed some light on this=2E
>=20
> thanks,
> John
> KA1XC
>=20
>=20
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