On 3/22/2014 7:13 PM, Jeff Liebermann wrote:
On Sat, 22 Mar 2014 08:47:56 -0700, Jon Danniken
wrote:

I don't have any professional experience with aircraft antennas.
However, I have done some ADS-B 1090 MHz designs and tests. The basic
idea is that the antenna should have the most gain at the horizon and
somewhat above the horizon to get the most range. Commercial jets fly
at about 5 miles altitude maximum, so gain in the upwards direction is
less critical. That's quite opposite of what the discone and
biconical will do.

I thought the discone/biconicals were more of a horizon-looking antenna,
at least from what I have read on them?

After I ran the NEC2 models, that seems true for the low end of the
frequency range. They are suppose to look something like a broadband
version of a vertical dipole. However, as the frequency goes up,
additional lobes appear until at the top of the frequency range, most
of the RF is going straight up. A Biconical is somewhat better than a
discone at retaining a sane looking pattern and reasonable gain, but
not much better.

My point about listening to aircraft is that there's little difficulty
hearing aircraft that are overhead, and plenty of difficulty hearing
aircraft near the horizon. Therefore, the antenna should have most of
its gain towards the horizon, and less gain above the horizon to near
overhead. At low frequencies, the discone does that. At the high end
of the range, it's quite the opposite.


There is? I remember back in the 70's a United Airlines pilot who would
regularly work 146.52. I had no trouble chatting with him from almost
300 miles away, even though he was only using a 1.5W HT. And out here
on the east coast, it's impossible to use an HT on any 2M repeater
frequency without bringing up multiple repeaters, even when using 1W
at about 3,000 feet or above. From 10,000 feet, forget it almost
anywhere in the country.

And BTW - commercial planes generally fly at around 7mi (35,000-37,000
ft.) high - not 5Mi (26,000 ft.) as you claimed.

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