[GreenKeys] OT: weather balloon telemetry

Paul Heller paul0926 at comcast.net
Thu Nov 7 23:07:41 EST 2013 

What a fun project. I look forward to reading about it in QST magazine! This just has to be published!

Paul

On Nov 6, 2013, at 10:07 AM, Chris Elmquist <chrise at pobox.com> wrote:

> Gil,
> 
> I agree that the TV twinlead J-pole may be a good option too, although
> at high altitude you will be looking into the end of it with most of
> its radiation going off perpendicular to you.   Think of a donut on a
> broomstick and you are looking down the length of the broomstick.
> 
> So, in my mind, not an optimal choice due to radiation pattern for the
> application but I'm sure it will still work.
> 
> Also, be careful to decouple the feedline (with ferrites or several turns
> of the feedline near the feed) of the J-Pole because it is a balanced
> feed antenna and you are feeding it with an unbalanced coaxial feedline.
> If you don't decouple it, then lots of RF comes back on the shield of the
> coax and the radiation pattern gets even less understood. Sometimes the
> RF coming back can also mess with your power supplies, microcontroller,
> the transmitter itself, etc.
> 
> Chris N0JCF
> 
> 
> On Tuesday (11/05/2013 at 10:38PM -0700), gil at baudot.net wrote:
>>   Hey Chris and everybody:
>> 
>>   Yes, 144.390 MHz for the APRS tracking system.  Gotta get my license
>>   asap now.  I was persuaded by those who know better to avoid the 433 or
>>   915 unlicensed stuff, and just do what works for many other
>>   balloonists.
>> 
>>   However, we want to keep the weight to the absolute minimum, so we can
>>   use smaller balloons and less gas to save money.  This means no heavy
>>   handheld radios or such.
>> 
>>   Currently, for the tracker encoder/transmitter, I am leaning towards
>>   the MicroTrak-400 from Byonics:
>> 
>>   [1]http://www.byonics.com/mt-400
>> 
>>   It weighs under an ounce, and just needs an antenna and a serial feed
>>   from the GPS.
>> 
>>   Byonics recommend their own "V6" dipole antenna (37" spring steel
>>   wire), but at $40 I would rather just make one, and a dipole is easy
>>   and cheap to make.
>> 
>>   Your turnstile crossed dipole idea sounds interesting.  I have
>>   previously considered an x-shaped payload base using 1/4" square wood
>>   dowels from home depot (which seem stiffer than round dowels, and
>>   weight only 0.5 oz for a 3-ft piece).  I have adhesive-backed copper
>>   tape that could stick to one side of the square dowel to make a
>>   lightweight dipole, or crossed dipole, and solder thin/lightweight
>>   RG-174 or 178 feed coax directly to it (and, for the turnstile, make
>>   the 75-ohm phase section out of RG-179).
>> 
>>   I have been reading up a lot on all of this the last day or so, and
>>   getting quite a few recommendations:  a basic (horizontally-mounted)
>>   dipole, a simple inverted 1/4 wave vertical hanging down with ground
>>   wires forming a plane, an inverted 5/8 wave vertical, a patch...
>> 
>>   Some balloon guys say to use a twinlead version of a J-Pole, like this:
>> 
>>   [2]http://www.hamuniverse.com/2meter300ohmslimjim.html
>> 
>>   This sounds light, cheap, and easy to hang, and it only needs to handle
>>   less than 1/2 W tx pwr.
>> 
>>   I guess the big question is which antenna has the best propagation from
>>   way up there -- looks like we are going to attempt three different
>>   missions, to 20,000, 60,000, and 90,000 feet.
>> 
>>   Please pardon the OT posts, but we have a lot of hams on greenkeys, and
>>   I sure appreciate the advice.
>> 
>>   thx,  gil
>> 
>>   gil smith
>>   greenkeys moderator
>>   [3]gil at baudot.net
>> 
>>   -------- Original Message --------
>>   Subject: Re: [GreenKeys] OT: weather balloon telemetry
>>   From: Chris Elmquist <[4]chrise at pobox.com>
>>   Date: Tue, November 05, 2013 3:05 pm
>>   To: [5]gil at baudot.net
>>   Cc: [6]greenkeys at mailman.qth.net
>>   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,
>>   [7]http://www.west.net/~jay/turnstile.html
>>   Chris N0JCF
>>   On Tuesday (11/05/2013 at 08:49AM -0700), [8]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][9]gil at baudot.net
>>> 
>>> References
>>> 
>>> 1. [10]mailto:gil at baudot.net
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>>   --
>>   Chris Elmquist
>> 
>> References
>> 
>>   1. http://www.byonics.com/mt-400
>>   2. http://www.hamuniverse.com/2meter300ohmslimjim.html
>>   3. mailto:gil at baudot.net
>>   4. mailto:chrise at pobox.com
>>   5. mailto:gil at baudot.net
>>   6. mailto:greenkeys at mailman.qth.net
>>   7. http://www.west.net/~jay/turnstile.html
>>   8. mailto:gil at baudot.net
>>   9. mailto:gil at baudot.net
>>  10. mailto:gil at baudot.net
>>  11. http://mailman.qth.net/mailman/listinfo/greenkeys
>>  12. http://mailman.qth.net/mmfaq.htm
>>  13. mailto:GreenKeys at mailman.qth.net
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>>  15. http://mailman.qth.net/archive/greenkeys/greenkeys.html
>>  16. http://comcents.com/tty/greenkeyssearch.html
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> 
> -- 
> Chris Elmquist
> 
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