[Milsurplus] receivers

Sun, 2 Nov 2003 19:30:43 -0500

You're talking about the "relatively insensitive broad band IF" receivers, I
assume, in the WW2 and immediately following period. This is too much of a
generalization, as selective, relatively stable and sensitive receivers were
also procured, and used in WW2. The relatively insensitive and broad-band
receivers were mission specific, teamed up with relatively unstable
transmitters, which were subjected to vibrations in the field and in
aircraft and ground vehicles, under combat conditions. The fixed receivers
were sensitive, selective and as stable as the prevalent state of technology
permitted. You can't compare a BC-348, BC-312, RBS or RBM with a BC-1004
(Hammarlund Super Pro 200), with an RCA AR-88, with a Navy RBB and RBC or a
military National HRO and derivatives selectivity, and sensitivity-wise.
There were other high-end receivers also in use by the military, which I
haven't mentioned.
SIGINT existed of course in WW2 and some of these receivers were used for
intercept. There were also long-haul radio traffic circuits which used the
best available receivers.
The big innovation in receiver (and, transmitter) technology was the stable
Permeability Tuned Oscillator (PTO) by Collins which appeared in WW2 in the
ART-13 transmitter. In the late 40's Collins came out with the 51J receiver
which was the standard by which the receivers were measured. By the early
50's the BC-610 transmitter was paired up with the R-388 (military Collins
51J-3). The BC-610 went through a few receivers (won't mention the various
system SCR and later GRC numbers) from early WW2 until the end of its life
cycle: SX-28A, BC-312, BC-342, and R-388.
The R-390 and later the R-390A, (the less expensive version...) were the
natural evolution of a typical Collins receiver concept, ruggedized and
modularized for the military
But the Veeder-Root counter is also a natural evolution of the linear scale
with the fiduciary coupled to the linear PTO as in the 51J series.
The BC-610/R-388 was replaced with the T-368 using the Collins linear PTO
system, also with a direct mechanical-digital frequency readout as the R-390
which was used as its companion receiver. The R-392 was also developed at
the same time as a smaller version of the R-390 for mobile use, with the
same frequency display as the R-390 and  running the plates and filaments
from 24 VDC. Its companion transmitter was the T-195, with the linear
Collins PTO and also the Veeder-Root frequency display.
The R-390 was definitely used for SIGINT intercept, but I don't believe that
was the primary purpose of its development. It simply had to replace the
older technology (and the Cold War started in earnest) and it utilized the
latest available technology. Its excellent characteristics are a result of
the then available technology and components which were utilized in the
design.
There were other receivers manufactured in Europe, (such as the Racal RA-17,
Rohde & Schwartz EK-07, Telefunken E 104/KW and others) which were at least
as sensitive, selective and stable (in fact, more) as the R-390 but were
more complicated and not as easy to service. They were used both by the
military/government and the civilian market for long-haul communications,
and intercept.

Hammarlund/Hallicrafters/TMC and others had some good products which were
used by the government and the military, as well as the civilian sector, but
because Collins had the patents on the PTO and the frequency conversion
scheme of the Collins systems, Collins remained the leader in the
stability/frequency readout game, until of course the Phase Locked Loop
(PLL) synthesizers left analog frequency generation by the wayside.

My 2 cents' worth...

73, Meir WF2U
Landrum, SC

-----Original Message-----
From: [email protected]
[mailto:[email protected]]On Behalf Of aGEnuine Ham
Sent: Sunday, November 02, 2003 5:43 PM
To: [email protected]
Subject: [Milsurplus] receivers

Group:

The discussion about the genesis of the R-390 series receivers arises
regularly, and various reasons are proffered for the rationale of its
appearance.  Let me offer the following:  Most receivers designed for
military use are relatively insensitive, broad band IF (i. e., easy to
tune), and field repairable, by design.  The 390 hardly fits.  A current
example of military receiver sensitivity popped up in some shipboard work
I was recently involved in, and I took a close look at the SPAWAR
sensitivity specifications on current procurements of shipboard DF.  Not
very sensitive.  Accurate bearings, but doesn't respond to weak signals.*

So where is this diatribe leading?  The reason the R-390 is so desirable
for ham and similar use is that it is unusually sensitive while
exhibiting good rejection of unwanted signals (high dynamic range, unlike
most present production equipment), the frequency calibration is
excellent for the era, it has lots of flexibility in IF bandwidth, and so
on.  So who would be the target market for this design in 1950?  There is
only one answer, and it is not tactical or even strategic military
communications.  It is spelled SIGINT.  And, back when those designs were
initiated, no one could even whisper NSA in public.  So, the genesis of
these boxes remains shrouded in the tight Cold War secrecy of the time,
and it is difficult to refute most of the wild stories which arise in the
vacuum of this lack of factual information.  But, that venue had the
quantity of funds necessary to initiate an expensive design like the 390,
while the rest of the military suffered along with tactical equipment of
much lesser performance which was typical of the time.  I had a friend
who repaired BC-610s at night in the stream beds in Korea in this time
frame, the SCR-x99 series being still a mainstream radio system.  There
are several other products which were funded in the same time frame, some
of which remain classified, and others which are no longer held close,
but have all been destroyed and the hardware has never been seen by the
public, except perhaps in the NSA museum.  I'm still looking for a meter
from an FLR-13 (WARS), for example.  Finally, the way the security
process works, most if not all of the people who actually worked on those
products in the early days signed lifetime nondisclosure agreements, and
it is likely that they have never been officially notified that the
information has been declassified, so they *could* still be prosecuted
for violation of the secrecy laws if they chose to go public with their
knowledge.  And, these days, with the prevailing Federal attitude about
such, I for one, would not take the chance.

Hammarlund independently continued their successful Super-Pro line with
the various versions of the SP-600, and that design was preferred by some
operators based on easier band changing, and more familiar tuning
characteristics.  But, the dial calibration was not as accurate, and the
390A, with the mechanical filter(s) also gained a notch on the
selectivity battle.  Hallicrafters built their version of the R-274 and
called it a SX-73, but it suffered some of the same shortcomings of the
SP-600, particularly dial accuracy.  TMC popped up with their HF line
about this same time, and other short lived HF radio designs also
appeared.  Has anyone ever wondered where the market was for all these
high performance HF radios?  Hams? Point to point? Maritime? I submit
that the actual market was invisible to most people, except for the few
in certain carefully chosen locations.

*  There is actually good justification for this (according to SPAWAR).
The fog of war at sea produces a plethora of signals, and DFing on
intermod products of friendly transmitters and the like is distracting
and undesirable.  Also, the signals of interest are 'usually' submarines
within torpedo range.  So, relatively strong ground wave (sea wave?)
signals provide the targets for shipboard DF, and higher sensitivity than
required to accomplish this mission is undesirable.

73,
George
W5VPQ