[GreenKeys] OT: weather balloon telemetry

[Chris Elmquist]

So, you are going to downlink on 2m?  144.390?

You might consider a crossed-dipole (sometimes referred to as a
"turnstile") antenna which will give you circular polarization and
reduce fade if the balloon is spinning.  It will be 3dB down from a
linear polarized antenna on the ground but if there is any spin, it will
not go through peaks and valleys as the two antennas go in and out of
polarization alignment.

It will then also be "flat" on the bottom of the balloon (would look like
a "+" as you look up at the bottom of the balloon) and then won't stick
in the ground when it comes down but instead be a little like landing
gear :-)

Here's one discussion,

http://www.west.net/~jay/turnstile.html

Chris N0JCF

On Tuesday (11/05/2013 at 08:49AM -0700), gil at baudot.net wrote:
>    OK folks, after some good info from several of you, it does sound like
>    using 144.390 MHz APRS tracking would be the best bet for this balloon
>    project.
> 
>    This means I need to study for a ham test now, but they seem to be
>    offered frequently enough, so I guess I will need to start learnin'
>    some new stuff!
> 
>    Back to my question about antennas:  what to hang under the balloon?
>    It has been pointed out how it needs to be omni.  I suppose the
>    simplest would be a 1/4 wave hanging down, and suspended by three or
>    four angled ground wires that connect to a simple
>    three-or-four-radial-dowel frame or something.  The antenna would
>    collapse on the ground (of course we hopefully have GPS coordinates for
>    the descent, so we can find it).
> 
>    Any other antenna recommendations?  Dipole?  Patch?  Nothing commercial
>    -- something I can fabricate out of lightweight wire or foil.
> 
>    thx,  gil
> 
>    gil smith
>    greenkeys moderator
>    [1]gil at baudot.net
> 
> References
> 
>    1. mailto:gil at baudot.net

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-- 
Chris Elmquist