[Antennas] 2m antenna for airborne transmitter?

[Jim Hargrave]

Florin

I would suggest you make a J Pole antenna using 300 ohm TV twin lead.
Its easy to build. It is light weight and can trail below the balloon. Just
trail it upside down.

One article is at: http://www.qsl.net/wb3gck/jpole.htm


    73s de Jim
       W5IFP


  > -----Original Message-----
  > From: antennas-bounces at mailman.qth.net
  > [mailto:antennas-bounces at mailman.qth.net]On Behalf Of Florin Andrei
  > Sent: Wednesday, November 23, 2011 1:41 AM
  > To: antennas at mailman.qth.net
  > Subject: [Antennas] 2m antenna for airborne transmitter?
  >
  >
  > I am putting together plans to launch a high-altitude balloon some
  > time next year. It may reach 30km altitude, covering 1x ... 10x as
  > much ground horizontally, for a total flight duration of 2 ... 3
  > hours. The payload is supposed to gather various data (temperature,
  > pressure, humidity, etc.) and log it locally to an SD card. GPS data
  > will be relayed to the ground over APRS on 144.390MHz. The brain of
  > the payload will be an Arduino. The transmitter will probably be one
  > of those lightweight small modules that take 5V CMOS input on one pin
  > and modulate a 50ohm RF output on another pin - something similar to
  > this:
  >
  > http://www.radiometrix.com/content/hx1
  >
  > I intend to relay GPS data to the existing APRS network on the ground,
  > and track the payload from an Internet-connected portable device. But
  > the tracking vehicle will also be equipped with an FT-817 and a laptop
  > and will receive and decode APRS data from the balloon independently,
  > as a backup system. I still need to fine tune many details related to
  > APRS itself, since I've never done it before, but that's another topic
  > for another forum. I live in the San Francisco Bay Area, so at least
  > for a while the payload will fly above a dense APRS network.
  >
  > The thing is, I'm not sure what's the best antenna to use on
  > the balloon.
  >
  > Obviously, it needs to be as lightweight as possible. The balloon
  > doesn't generate much lift, so any weight savings are welcome.
  >
  > Large, rigid, sprawling structures are not good either, even when they
  > are not heavy. There are strong winds at high altitudes, and a large
  > antenna may spin the payload excessively.
  >
  > Ideally, I'd like the antenna to more or less survive touchdown after
  > a long descent on a parachute - this is in case I lose signal on the
  > last part of the trajectory, I'd like the beacon to keep transmitting
  > after touchdown, so I can locate it with my transceiver in the woods
  > or on a farm or wherever it may fall.
  >
  > Finally, the radiation pattern should be a big wide lobe, facing
  > downward, extending from horizon to horizon in all directions. That, I
  > guess, is probably not 100% realistic, but I'd like to stay close to
  > the ideal.
  >
  > One thing I could think of is a 1/4 wave ground-plane whip. I could
  > use thin aluminum tubes to make the elements. Should I keep the
  > "ground plane" elements parallel to the ground, or should I bend them
  > 45deg upward?
  >
  > Another idea: the balloon could trail a thin long wire. That design
  > works okay in HF, but I'm not sure how to make it work in 2m, with a
  > 50ohm output transmitter, lacking a true ground connection.
  >
  > For the tracking vehicle, again, probably a 1/4 wave ground plane?
  > Aiming at the balloon with a 2m Yagi from a moving sedan - that
  > doesn't sound like a sane idea to me. :)
  >
  > Any suggestions, comments, hints, are appreciated. Thank you.
  >
  > --
  > Florin Andrei
  > KG6YHQ
  > http://florin.myip.org/
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