[Date Prev][Date Next][Thread Prev][Thread Next] - [Date Index][Thread Index][Author Index]

Re: I have an idea. Please read



In a message dated 6/13/00 7:26:52 AM Mountain Daylight Time, kg5za@juno.com 
writes:

>      If the foot print is only 300 miles at 100,000 feet as you say, then
>  how is possible that I can work a friend air Mobile , simplex, on 2M, 
>  coming out of Houston Hobby airfield  (nearly 600 miles away) when he
>  hits 20,000 feet in a  Saber Liner?   Kinda make ya wonder doesn't it. 
>  We do this routinely.

Midland and Houston are 437 miles away from each other as the crow flies.   
Being a pilot, I am somewhat familiar with air-to-air propagation distances 
and if this were to occur on the 2M band, it should also be possible on the 
aviation band which is pretty close (118-135 Mhz).  The predicted radio 
horizon at 20,000 feet is 200 miles.   I seldom hear air traffic from more 
than 250 miles away and that would be consistent with a radio horizon for 
cruising altitude of 35,000 feet.  Of course, your radio might be a lot more 
sensitive than mine. 

There may be a some other factors at work here.  It takes a little time to 
get to 20,000' and in a fast jet like a SaberLiner, he's likely to be 50 
miles away from Houston when he reaches that altitude.  If he's flying in 
your direction, that could account for a few of those miles.  That's still 
nearly 400 miles which is about twice the radio horizon.  The radio horizon 
formula, d = sqrt (2 x height);  where d is in miles and height is in feet)  
takes into account the atmospheric diffraction that generally adds 15% beyond 
the visual range.  Next time you work your friend in the Saberliner, ask for 
his position with respect to some navigational beacon or his coordinates  
since it would be very interesting to see how often this kind of ducting 
takes place down your way.  I suppose it may even be possible that your 
signals are bouncing off of other air traffic in the area.  I'd also be 
curious as to what type of antennas, radios, and power you're both using.

If 600 mile radio horizons were commonplace at 20,000 feet, it would wreak 
havoc with air traffic control since they 're use' aviation frequencies at 
various air traffic control facilities across the country and there would be 
a lot of overlap, particularly if it were to scale up to 35,000 feet which is 
where most commercial air traffic cruises.

Lee Devlin, KØLEE  (K0LEE)
Greeley, CO
http://members.aol.com/lee810/ham.html
----
Via the amsat-bb mailing list at AMSAT.ORG courtesy of AMSAT-NA.
To unsubscribe, send "unsubscribe amsat-bb" to Majordomo@amsat.org



AMSAT Top AMSAT Home