[Milsurplus] [ARC5] Opinions on ARR-7

[Mike Hanz]

Well, the receiver doesn't appear to have been desensitized all that 
much.  The ARR-7 manual claims "better than 10uV at a 10dB S/N ratio on 
all bands with a 50mW output."  That contrasts with that original SX-28 
spec of "2mV for bands 1-5 and 4mV for band 6", and the SX-28A claim of 
"6-20uV" (admittedly with 500mW output) over the receiver's entire 
range. No S/N figure is stated for the SX-28 versions.

I'm not sure the ARR-7 was ever used for radar work.  The VHF ARR-5 was 
indeed used for radar collection efforts, at least at the first part of 
the war when German and Japanese radars were comparatively low frequency 
in operation, but that changed rapidly with the Germans, and even the 
Japanese eventually migrated to higher radar frequencies above the range 
of the ARR-5.  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..." :-)   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...  The lower frequency airborne jamming 
efforts quickly settled into the frequencies above 30MHz, primarily to 
counter missile guidance systems.

73,
Mike

On 8/27/2012 2:56 PM, J. Forster wrote:
> It seems the set was designed as an ELINT receiver for detecting and
> analyzing enemy HF RADARS. As such, sensivity is not really at issue. Even
> a receiver with no RF stages can easily see a RADAR looong before it can
> possibly see you.
>
> -John
>
> =================
>
>
>> I did make one small
>>> modification to it - jumpered plate and grid of the anti-radiation
>>> isolation stage with a small mica capacitor soldered to a couple of tube
>>> pins inserted into the tube socket. The original design simply added a
>>> bunch of noise to the receiver without any useful purpose.  I made the
>>> same change to the ARR-5 input stage.  Pairing with an AN/APA-10
>>> panadapter and an APA-6 or -11 pulse analyzer is an interesting thing to
>>> do if you have the space and power.  I normally use it with an
>>> interphone amplifier to get the power for a speaker - the LS-184/AIC-10
>>> - but any outboard amp can of course be used.
>> The Navy was paranoid about oscillator leakage being picked up by the
>> enemy
>> and had many receivers modified with an additional RF stage, tuned or
>> untuned. From what Ive read on the subject it is highly doubtful that the
>> enemy had sufficient technology during WW2 to detect it unless they were
>> well under a half mile away.
>>
>> Perhaps, also, the ARR-7 was deliberately desensitized to limit
>> interference
>> from distant signals as well as minimize images due to only a single tuned
>> RF stage that plagues many receivers on the higher frequencies when using
>> only a 455kc or similar IF.
>>
>>
>
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