[Milsurplus] 1 mo Eb*y / BC-645 aka ABA

[William Donzelli]

> One unmentioned one is right.  Legislation
> 
> Allies decided on MkIII 160-190mhz frequency/code-agile system early
> o.  An amazing British system.  Really amazing.  Would be hard to 
> clone/dupe today with PLL & sw-defined radios.  The delta-f over F was so
> dang big.

I think the adoption of Mk III IFF was really a poor choice. It was quite
a kludge, and on top of that, not very secure.

The official reason for the non-use* of the Mk IV system was that its
operation was too close to the German Wurzburg radars operating
frequency. This it was - with some modifications, a Wurzburg probably
could pick up Mk IV pulses (I don't know if this was ever done).

Mk III IFF, however, turned out to be close to the operating frequency of
the Freya radars. Too close, it seems. Freyas were modified so they could
pick up Mk III pulses, and the system was comprimised without the Allies
knowledge. 

* Mk IV was used in the Pacific. I have one ABA-1 that did see service,
getting the infamous "deface the date" on the nameplate. Likewise, the
Navy issued modification kits to the Mk III model BN interrogators to turn
them into Mk IV model BP boxes. Mk IV was also made for shipboard duty,
although I do not know if any saw service. The shipboard version of the
ABA-1 is known as BA. Additionally, there was a BE/BF pair for shipboard
Mk IV IFF.

William Donzelli
aw288 at osfn.org