At 08:11 AM 20/06/05 +1000, you wrote:
>Mike
>
>
>Understand the mechanics of how the transmitter works which surprises me
>considering your usual good understanding of the subjects you comment on,
>the quoted output at 70 watts is peak power, not average. The average based
>on a 112us message, which has about 50% only containing either a .5 or 1us
>pulse, averages out at only a few watts. Boeing have conducted tests on EMR
>from these devices and concluded that after a distance of 2 inches no
>appreciable levels are of any concern.
I know that, I can do avergae power calculations too. There are two
possible effects of RF radiation:
1) heating - and you are absolutely correct, the average power level is too
low to be of concern as far as bulk heating effects go.
2) Effects on large organic molecules. In this case it is the peak power
that is of concern. Adrian knows guy in CSIRO who manipulates large organic
molecules in gel with RF power pulses at around a gig. Large organic
molecules in gel pretty well describes the human body.
This sort of thing, not bulk RF heating is what concern about cellphone
emissions is about and AFAIK cellphones do not have an unambiguous clean
bill of health.
The Boeing assurances appear to be based on bulk heating effects.
I'd really like an independent biochemist/biologist team to give these
assurances after running some targeted research, not just RF engineers.
>
>
>My company was the one who got up at the ABIT meeting and proposed the lower
>output power so I have the information first hand. The Boeing data was
>supplied by Boeing, who were also at the meeting. So was Bob Hall, albeit
>uninformed and a wasted his time as he had done no preparation or research
>into ADS-B, although I think he now has a better understanding of what is
>going on, he also had a look at our handheld ADS-B unit, which runs on 4 AA
>batteries for 4 to 5 hours - sort of discounted his belief that to power
>ADS-B you needed a small nuclear reactor.
>
>Remember Mike I am at the coalface, so to speak so working on Pulse L band
>transmitter design is what I do daily.
I have no doubt that an ADSB transmitter can be made that won't require too
much power to be fitted to a glider, you proved that with the Microair
transponder.
My concern about ADSB apart from high power RF pulses is that it is now a
fairly old standard designed primarily to replace secondary radar,
primarily for the benefit of Airservices in cost savings although when
controllers can see things they want to control them so I doubt that these
cost savings will be realised. Because of the radar substitute requirement,
the specification of the airborne equipment is many times what is necessary
for a stand alone air to air collision avoidance system.
We now have a snowball effect with an alliance of convenience between the
air traffic control union, equipment suppliers ($50 to 100 million up for
grabs) and organisations like Boeing and BAe who want to operate large
UAVs in any class of airspace with few restrictions. Sport aviators and the
low end of GA don't count. Airservices own cost benefit analysis showed no
benefit to GA and sport aviation of fitting ADSB transmitters. The subsidy
promise is pretty vague and anyway after the fitout of the existing fleet
new aircraft ownwers will have to pay for their own. Everybody happy about
doubling the avionics budget for their new glider?
Mike
Borgelt Instruments - manufacturers of quality soaring instruments
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