On Thu, 19 Nov 2015 00:23:16 +0000, Steve
wrote:
With a RTL SDR type USB stick on its way, I turned my attention to
looking for an antenna with high gain that would give me good coverage
of ADS-B 1090 MHz broadcasts from aircraft, one that I could easily
and cheaply make for myself.
Here are some NEC2 models of some ADS-B antennas. We've built a few
and they work well.
http://802.11junk.com/jeffl/antennas/AMOS-3-INV-1090Mhz/index.html
http://802.11junk.com/jeffl/antennas/AMOS-5-1090MHz/index.html
http://802.11junk.com/jeffl/antennas/AMOS-5-INV-1090MHz/index.html
The front end of the typical RTL2832U SDR gizmo seriously lacks
dynamic range. If you install a high gain antenna, with a pre-amp to
compensate for the coax losses, in a location with a good view of the
sky, you're going to overload the receiver front end. You're also
going to experience some front end overload and possibly intermod from
other services using the same L band range such as TCAS radar,
JTIDS/MIDS, and DME. Cavity filters are a big help.
For starters, I suggest a very simple antenna with coverage of the
sky. There's plenty out there to hear and you won't be bothered by
overload and interference. Once you have a good idea of what software
is the lesser evil, and you find your range to be inadequate, think
about big antennas, preamps, and filters.
A quick google produced loads of hits for this type of antenna.
https://www.youtube.com/watch?v=TkUYdCPFXXs
as a random one. You get the idea.
Retch. Those are alternating coax cable collinear antennas. For a
given length antenna, they have 3 dB less gain than a collinear
antenna made with coils or 1/4 wave stubs. The coax flavor are also
end fed instead of center fed, making it difficult to put the main
lobe at the horizon, instead of a few degrees above the horizon (i.e.
uptilt). The good news is that it will have a lousy pattern and low
gain, which should reduce overload and interference problems. If you
really want to build something like that, test the antenna to see
where it's tuned with a sweep generator, directional coupler, RF
detector, and an oscilloscope. The one's I've seen, that were built
without a fixture, look awful.
Good luck.
--
Jeff Liebermann
150 Felker St #D http://www.LearnByDestroying.com
Santa Cruz CA 95060
http://802.11junk.com
Skype: JeffLiebermann AE6KS 831-336-2558