Interesting old antenna, could use help identifying

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bobasaurus
Posts: 23
Joined: Wed Dec 27, 2017 4:36 am
Location: Colorado

Interesting old antenna, could use help identifying

Post by bobasaurus » Wed Dec 27, 2017 5:45 pm

We have this interestingly-shaped old antenna at work:

Image

There is an N-type connector on the bottom, and threads for mast mounting to a threaded pipe/pole. The J piece is attached with setscrews, possibly adjustable in height a bit.

I was told that it might be an old radiosonde antenna, but nobody was sure. Any idea what type of antenna this is, and what frequency range and directionality/pattern it might have? I'm not very knowledgeable about antennas, I would appreciate the help.

I once used it to receive 404 MHz radiosonde data from one of our weather balloon launches and it seemed to work decently.

bobasaurus
Posts: 23
Joined: Wed Dec 27, 2017 4:36 am
Location: Colorado

Re: Interesting old antenna, could use help identifying

Post by bobasaurus » Wed Dec 27, 2017 9:26 pm

Some reddit users came up with the answer: it's a folded monopole antenna. There is some confusion about whether it's a 1/4 or 1/8 wave on the top section for determining the frequency.

rtlsdrblog
Site Admin
Posts: 2432
Joined: Mon Nov 19, 2012 11:54 pm

Re: Interesting old antenna, could use help identifying

Post by rtlsdrblog » Thu Dec 28, 2017 1:14 am

Yep folded monopole. Do you have access to an antenna analyzer or VNA? Even a noise source + directional coupler + RTL-SDR could help. https://www.rtl-sdr.com/rtl-sdr-tutoria ... se-source/

Then you could identify the resonant points of the antenna and know for sure what frequencies it was designed for.

snn47
Posts: 192
Joined: Tue Dec 27, 2016 11:00 pm

Re: Interesting old antenna, could use help identifying

Post by snn47 » Thu Dec 28, 2017 10:41 pm

Folded Ground Plane, Folded Monopole
think of it as a folded fullwave dipole cut in half on a groundplane (using 1/4 wave elements), similar to a round plane is a half wave dipole cut in half on a groundplane.
Unlike most groundplane antennnas using a 1/4 or 5/8 lambda radiator, the benefit is that the antenna element does not have a sharp tip and less likely to attract lightning, and is grounded.
Some links and discussion can be found here http://www.eham.net/ehamforum/smf/index ... 373.0.html

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