[Milsurplus] Opinions on ARR-7. (Excerpt From Secret WWII Publication)

[Mike Morrow]

>From "Graphic Survey of Radio and Radar Equipment Used By the Army Air Forces,
Section One, Countermeasures Equipment", dated 1 February 1945 (SECRET):

"RADIO RECEIVING SET AN/ARR-7

"Radio Receiving Set AN/ARR-7 is an airborne intercept receiver covering
the frequency band 550 kc. to 28 mc.  The set has been adapted from a
Hallicrafters SX-28 receiver omitting the band switching units used in
the commercial receiver for reception above 28 mc. repackaged in a
Standard Aircraft Radio Case B1-D.  It is used in conjunction with Radar
Indicator Assembly AN/APA-6 or AN/APA-1l and Panoramic Adaptor AN/APA-10.
Provision is made for an automatic scanning unit that can sweep through the
whole frequency band.  Power is obtained from Rectifier Power Unit PP-33/AR
for 110 volt, 60 c.p.s. operation or from PP-32/AR for 85-100 volt, 400 to
2600 c.p.s. operation.  

"The receiver has an output of greater than 50 milli-watts for 10 microvolts
impressed on the input terminals of the receiver.  It is extremely sensitive
for continuous-wave and amplitude modulated signals.  It operates on AM, FM
and CW, and provision is made for broad or sharp tuning.  Automatic volume
control and noise limiting circuits are incorporated in the set.

"To adapt the equipment for use with panoramic adaptors a lead is brought out
from the plate circuit of the mixer stage to the proper receptacle.  Video
output is obtained by a lead through a cathode follower resistor from the
cathode circuit of the power output tube.

"The sector sweep or scanning mechanism consistsof a motor assembly, a magnetic
clutch, a gear train and a sector selecting mechanism.  When the motor is 
operating the magnetic clutch locks the gear to the tuning dial shaft.  When
the motor is switched off, the magnetic clutch is not energized and the tuning
shaft is free of gears, making manual tuning possible.

"Army Supply Program requirements as of 31 July 1944 were 2,060 equipments for
the calendar year 1944 and 2,163 for 1945.

"Test equipment required for the maintenance and tuning of the equipment includes
Signal Generator TS-47/APR, General Radio Signal Generator Type 804C, Signal
Generator 1-72 and Hickok Voltmeter Type 110.

"FREQUENCY 550 KC. to 28 Mc.
POWER INPUT 175 WATTS
TYPE OF SIGNAL AM, CW, Pulse
SENSITIVITY 5 MICROVOLTS
TENTATIVE TUBE COMPLEMENT
1 6AB7
4 6SK7
2 6SA7
1 6SQ7
1 6H6
1 6J5
1 6V6GT/G
1 VR/150/30
3 5U4G or 5R4GY (for power supply)

"Component            Nomenclature
Receiver              R-45/ARR-7
Rectifier Power Unit  PP-32/AR
Antenna Support       AB-27/A
Mounting Base         MT-167/U
Mounting Base         MT-171/U
and includes plugs, adapters, cables, tension unit, wire thimble."

Notice that the mythological PP-33/AR 60 c.p.s. power unit is mentioned
in the description.  I suspect it never saw deployment...the publication's
description for the companion AN/ARR-5 mentions only the PP-32/AR.

This publication also shows a B-17 installation of the AN/ARR-5,
AN/ARR-7, and PP-32/AR, along with AT-38/APT for the AN/ARR-5, and
apparently a wire antenna for the AN/ARR-7.

Mike Hanz wrote:

> ....The compendium "Radio Countermeasures", one of the 
> classified NDRC reports issued following the war, has it listed 
> tentatively under the category of radio communications countermeasures, 
> which is consistent with your ELINT proposition, but more focused on 
> identifying signals that could be subsequently jammed by airborne 
> jammers down in the passband of the receiver.  "If you can't hear 'em, 
> you can't jam 'em..." :-)

One must wonder what transmitter would have been intended for jamming
anything within the MF/HF spectrum of the AN/ARR-7.  There were jamming
tuning units for use with the SCR-287-A (BC-375-*) that covered all 
together from 2 to 30 MHz:

TU-60
TU-63-T1
TU-64-T1
TU-65-T1
TU-66-T1
TU-64-T1

There was also a proposed AN/ARA-3(XA-1) jamming modulator for use with
the SCR-278-A.  I could swear I've heard of a MD-30?/ARA that was actually
used, bt I can't find any record now.

> The operational history didn't seem too successful in using airborne
> platforms for radio communications jamming, however.  It appears that
> ground intercept and jamming was more effective, probably because it's
> pretty hard to get a decent sized antenna to behave in flight...

My sentimental favorite airborne jammer is the RT-45/ARQ-1 (14 to 50 MHz).
I wonder if any were ever actually used.  I like your 2010 response to a
posting on the Antique Radios forum:

> The Sandy jammer was intended to jam German AM ground communications
> from airborne platforms, one of a series of such jammers developed
> at a feverish pace in 1944 and early 1945. The pace was so great that
> numerous separate projects were being worked on simultaneously, so the
> natural result was multiple capabilities being delivered at the same
> time. The ARQ-1 provided roughly 20 watts of output power over a bandwidth
> of 40-150kHz, the power fairly well distributed across both sidebands.
> I don't believe it saw wide use, because low power made it problematical
> for jamming effectiveness, and it was quickly eclipsed by both the ART-2
> and ARQ-8 as the "go-to" equipment for the job. A Class B linear
> nomenclatured the AM-66/AR-XR was developed to raise the power output to
> 500 watts, but it was never fielded in any quantity either. 
>
> It is actually possible to remove the noise tube and substitute a microphone
> in its place for AM use. The result isn't a bad little transceiver, if you
> can live with the broad receiver selectivity and transmitter frequency drift
> with key down. All of these problems respond to some thoughtful reversible
> add-ons, but of course the biggest problem is usually the 400~ power source.
> I would hate to see a NIB unit receive the drastic mods usually meted out to
> them by hams trying to make a silk purse out of a sow's ear, though. It is
> what it is, and can provide some interesting hours of fun without serious
> surgery. A maintenance manual would be a plus - I have never been able to
> find more than the operator's manual.

I guess that the JAN "AN/ALx-xx" nomenclature appropriate to all this stuff was
not yet in use by the end of WWII.

73,
Mike / KK5F