[Milsurplus] ABK IFF Puzzle

[Mike Morrow]

Bruce MacMillan <radio at telus.net> wrote:
 
>This topic was discussed recently on the arc5 mailing list John. I 
>believe it was purposely marked as a receiver only to mislead the other 
>side.
>
>"The SCR-595-A IFF was simply a US Navy ABK Mark III IFF, without any
>Army nomenclature applied to the RT unit.  The SCR-695-A Mark III/G IFF
>unit was the BC-966-A.  The nameplates of all of these units bore the
>description of "RADIO RECEIVER" to mislead the other side.  But the USN
>ABK units also bear USN component numbers starting with "43" which is
>the component code for a "receiver-transmitter."  Not too consistent
>or deceptive!"

The quoted text above comes from one of my recent postings.  It's probably
best to attribute any direct quotes to the original writer, just in case
someone wants further information from that source or even wishes to say
that the information is full of crap. :-)

I have a manual for the ABK (and I have an ABK-5 unit), but unfortunately
I'm in the middle of a move and my 40 linear feet of tech manuals are in
moving boxes and won't get properly re-organized for some time to come.
The RF portion of Mark III IFF sets like the ABK was essentially a simple
receiver that was triggered into oscillation (and therefore transmitted a
return) upon receipt of an interrogation signal.  The frequency of operation
swept from 157 to 187 MHz using a capacitor driven by a gear box off of the
integral dynamotor unit.  The dynamotor also drives the response code keyer.
Six different response codes could be selected at the pilot's control box.

Some of the IFF gear from WWII is pretty interesting in concept.  Not all
were receiver-transmitters.  The AN/APX-15 on some B-29s was a signal
processing amplifier that detected fluctuations in the output from the
AN/APG-15 S-band tail-gun laying radar set.  The set would warn the operator
when fluctuations characteristic of reflections from the rotating propellers
of Japanese aircraft were detected.  Clever and very simple, but I've never
read any reports of how effective it was.

Mike / KK5F