[Milsurplus] tank radio skip?

[Bob Camp]

Hi

I have no problem with accepting some very amazing propagation from 
airborne platforms. The whole take off angle thing is potentially very 
different once you are well off the ground (say over 100 feet). Also as 
you get up to roughly 2,000 feet things like tropo ducting become a 
possibility.

On the transmit end I think we have established the transmitters being 
in the five or ten watt vicinity and running AM rather than FM. My 
rough survey of commonly available SWL grade VHF AM gear in 1941 is not 
terribly encouraging when it comes to sensitivity. Certainly I have 
experienced VHF openings and on many of them sensitivity was not an 
issue.

The question is not weather a single transmission could have been 
picked up. I will concede that it could have happened. The issue is 
weather enough transmissions could have been picked up over a long 
enough period of time to make setting up a detachment to monitor them 
worth while. Even with war time priorities it is hard to see things 
getting monitoring and communications set up in anything less than 
weeks. To be useful weeks or months of transmissions would have had to 
be intercepted and relayed back to North Africa.

Having a wide open band come on a path in the many thousands of miles 
range does happen. Having such a path come up regularly over say an 
entire summer at a less than peak point in the sunspot cycle still 
seems a bit much. Typical long haul openings seem to be a one day 
affair and then not much for a couple of weeks.

It would be nice to believe this happened (good old ham radio know how 
sort of thing). It just seems to be a bit past what seems likely ..

	Enjoy!

		Bob Camp
		KB8TQ

On Jan 30, 2005, at 12:09 PM, Mike Morrow wrote:

> Hue wrote:
>
>> I'm not sure what exactly the US FM equipment power was,
>> but they were certainly the most powerful of the tank equipment
>
> I think one can say with little fear of contradiction that U.S. 
> HF/VHF-FM
> gear was the finest tactical communication equipment in WWII.  The
> SCR-508/528 (BC-603/604, 20-28 mc) and SCR-608/628 (BC-683/684, 27-39 
> mc)
> were rated at 30 watts output, usually to an unloaded 10 foot whip.  
> These
> sets were really state of the art for their times.  It's a shame that 
> about
> the only people interested in them are military vehicle collectors.
>
> I suspect that in the first year of deployment of these sets, some
> surprising long range contacts were possible, especially with the 
> 20-28 mc
> sets.  Average solar activity for cycle 17 began downward in 1939, yet 
> it
> was still near its cycle peak, and minimum activity at end of cycle 
> didn't
> occur until early 1944.
>
> Several Vietnam War UH-1 pilots have told me of times when they could
> communicate on their AN/ARC-131 low band VHF-FM sets (30-76 mc) with US
> stations all over the Pacific, yet not to their intended station in VN.
> That agrees with effects from the peak of solar activity in cycle 20 
> from
> 1967 to 1971.
>
> Likewise, cycle 22's peak activity was from 1989 to 1992.  The report 
> of an
> aircraft in 1991 communicating with a base thousands of miles away 
> could
> very easily be accurate, if the attempted communication had been on 
> the low
> band VHF-FM sets that are standard equipment on many military aircraft,
> rather than the assumed UHF-AM aircraft frequencies.
>
> Mike / KK5F
>
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