[Milsurplus] Milsurplus Digest, Vol 163, Issue 30

[Jack Sullivan]

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Message: 2
Date: Mon, 13 Nov 2017 15:52:33 +0000 (UTC)
From: Jack Sullivan <wa1tej at yahoo.com>
To: "milsurplus at mailman.qth.net" <milsurplus at mailman.qth.net>
Subject: [Milsurplus] Spoof countermeasure against Japarception of
    proximtyity fuze signals
Message-ID: <1864307922.1043315.1510588353970 at mail.yahoo.com>
Content-Type: text/plain; charset="utf-8"

? My original question on this topic did not relate to the jammingof these projectiles - it had been shown that a modified APT-4 in a B-17 wouldcause premature? detonation of theseshells as observed from the aircraft. My question related to U.S. concern thatthe Japanese could pick up the signals radiated by the shells & develop inturn their own jammer or other countermeasure. I?ve read that in order tocounter this & to confuse potential Japanese eavesdropping, U.S. Navy shipstransmitted a number of ?spoof? signals in order to confuse them. This isobviously quite a different topic than jamming. I?m looking for any informationrelating to U.S. spoof transmissions & associated equipment used atOkinawa.Jack
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Message: 5
Date: Mon, 13 Nov 2017 11:59:58 -0500
From: Bruce Gentry <ka2ivy at verizon.net>
To: Milsurplus <Milsurplus at mailman.qth.net>
Subject: Re: [Milsurplus] Spoof countermeasure against Japarception of
    proximtyity fuze signals
Message-ID: <5A09CF8E.4030608 at verizon.net>
Content-Type: text/plain; charset="windows-1252"; Format="flowed"


Just how possible was it to receive the signals from the fuzes when they 
were hurtling toward you? The transmitters were of fairly low power, a 
good receiver would be needed, and even more challenging, knowing where 
to tune for a signal that might only last for ten seconds or so. How 
good was the state of the art for receiving UHF signals in 1944?  This 
question has come forward to me in the past week when I saw a 
Hallicrafters S-36, found it interesting, and  wondered if it was worth 
trying to find one of my own. How sensitive were receivers using acorn 
tubes or other UHF tubes of that time? I can attest from direct 
experience a BC-639 will break squelch with 3-5 microvolts of signal, a 
far cry from .3-.5 microvolts for good AM and full quieting FM of many 
two meter receivers in the 1970s. It was good enough to consistantly 
receive a ten watt transmitter on an aircraft in the traffic pattern. 
Because the no-signal hiss was so low on a BC-639, we often left them 
with the squelch open. How good were Japanese UHF receivers at that time?

      Bruce Gentry, KA2IVY

=====================================The need for proximity shell spoofing at Okinawa is borne out by reports returned to Japanese commanders that aircraft in an attacking formation were being destroyed even though there was no direct hit by an antiaircraft shell. Japanese pilots were selected for their excellent vision. I heard once that in order to qualify they had to pick out first-magnitude stars on clear days! With their eyes fixed on the stream of tracer shells coming up from the U.S. ships, there is no reason to dismiss this account. Whether or not the Japanese had the necessary intercept & subsequent jammer/countermeasure capabilities is open to question.The Japanese operated radar systems that operated in the 200 MHz spectrum, where the shells transmitted. A shell transmitting high above the sea, a gain 200 MHz antenna pointed at that area, who knows? But I have read that spoof signals were used at Okinawa to throw off would-be efforts at developing countermeasures, as we had with the APT-4 jammer.
Jack
   
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