On Fri, 21 Mar 2014 08:14:01 -0700, Jon Danniken
wrote:
Thanks Jeff, I had not considered a biconical, but it looks interesting.
The discone I am building is of a "spoke" variety, with the cone built
separate from the disk, so it would be simple to duplicate another cone
and invert it on top of the other cone.
If you want to be cheap and sloppy (like me), consider that a bowtie
antenna, commonly found on broadband TV antennas, is nothing more than
a flattened biconcial antenna. While it is directional, it's
functions much the same way as a biconcical and is much easier to
build (out of aluminum roof flashing).
I do like aircraft, although I am starting to think that I might be
better off with a dedicated airband antenna (looking at j-poles right
now) along with a wideband antenna for general scanning.
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.
Speaking of multiple antennas, I know that some antennas use multiple
elements tuned to different bands, but can you connect two antennas to
the same feedline? Like, say, a discone/biconical and a j-pole?
No. The best you can do is insert a diplexer at the feedpoint
junction, and separate the operating frequencies. Putting two
antennas in parallel doesn't work. If both antennas received the same
signal, the antenna pattern would be a conglomeration of both
antennas, which could just as easily result in a null as it could a
peak (also known as a mess).
I have such an arrangement at a site. 120ft of very expensive 2"(?)
Heliax going between the tower and the building. One triplexer and
three antennas, each on a different band, on top of the tower. Another
triplexer and 3 radios at the other end. Works so-so as intermod and
desense are a problem on some frequencies due to insufficient
triplexer isolation.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558