[ARC5] Re: [Milsurplus] History of Ham Mods: Opinions?

[Mike Hanz]

Marty Reynolds wrote:

>>To elaborate, there were four of the APS-13s in each weapon, in both
>>Little Boy and Fat Man - all having a different set of frequencies to
>>avoid interference.. There was an averaging system to account for spin
>>of the bomb casing in flight. The weaponeer could have switch selected
>>an alternate set of frequencies if Jacob Beser (the RCM officer) had
>>identified potential interference.
>>
>
>Mike I've read the 'averaging' was that 3 of four sets had to agree on
>altitude.  Provoking.  I've wondered just how with VT electronics.  
>

It was a little more complicated than that, Marty.  Remember that this 
weapon was built with WWII electronics, and they often failed in 
flight.  The task was to design a weighted system that would tolerate 
the failure of any two of the APS-13s while ensuring that the fuse would 
operate properly with any remaining two, so two had to agree that it was 
at the proper height, not three.  Their decision logic was used 
elsewhere in the weapon - called "series/parallel" logic, but the 
electronics used delay lines and gated times to detect coincidence.  The 
four APS-13s were turned on by a set of six redundant barometric 
switches that "voted" their output in a similar way to turn on power 
when the weapon reached 17,000 feet.  This also reduced the ECM exposure 
time of the weapon.  There was no backup fusing system, at least for 
Little Boy.  Tests had shown that the gun weapon was essentially 
"self-assembling" on contact with the ground, so that was the backup 
plan.  The whole process was started by a set of eight mechanical timers 
in a "Clock Box" that initially limited anything happening for 15 
seconds after it left the bomb bay...they were worried about radar 
reflections from the B-29 triggering the weapon in the event there were 
multiple failures of the baro switches and radars.

73,
Mike