[altusmetrum] Contact Form

John Sahr jdsahr at gmail.com
Mon Apr 18 19:49:44 MDT 2016


For what it's worth, one of the antenna design projects I offered in my
antenna class last year was a "telemetry antenna for high power rockets".
One team took up the challenge, and produced a quadrifilar helix that could
be mounted on the skin of a 4" fiberglass airframe; the idea being that
circular pol was a good idea, and that the interior of a high power rocket
was precious/dangerous.

I think I might try antennas embedded in fins as a student project for next
year.

jds

On Mon, Apr 18, 2016 at 10:39 AM, Bdale Garbee <bdale at gag.com> wrote:

> Web Customer <am-query at gag.com> writes:
>
> Copying the list since I've had this question before and getting a
> discussion going about different antenna ideas could be fun.  If you
> aren't already a list member, see the bottom of the altusmetrum.org page
> for a link to our list server and sign yourself up!
>
> > Comment: I have two of your TeleGPS units.  Last month I attended a
> > local HAM swap, which is something our Rocket club attends yearly to
> > create awareness for rocketry.  While there I thought I would ask
> > around for a suitable “base station” antenna for my TeleGPS, which I
> > had on display.  Someone suggested that I could get more range from
> > the antenna on the TeleGPS, because it was/is essentially only half of
> > an antenna and that I simply needed to add an equivalent length size
> > of wire to the ground side of the TeleGPS.  Does this sound correct?
>
> That's a gross over-simplification, and not the whole story.  It is,
> however, something you're likely to hear again in the ham community
> where the "default" antenna for many is the 1/2-wave dipole.  A 1/4 wave
> whip, which is what we're providing by default on TeleGPS and our other
> flight boards isn't "half an antenna", it's just an antenna built to
> different design criteria.
>
> Many books have been written about antenna design.  If you're interested
> in the topic, a good place to start would be the ARRL Handbook and/or
> one of the antenna books from the ARRL or RSGB.  Note that "conventional
> wisdom" in HF space doesn't always map well to UHF, so focusing on ideas
> that others have already discovered work well at 70cm could help narrow
> your focus.
>
> Antennas in rockets get complicated by a lot of things, including the
> dielectric influence of airframe materials, proximity of other metal
> like all-thread in ebays, etc.  After trying a bunch of things, we think
> the simple wire 1/4-wave whip is a pretty good choice.  However, I've
> done some "creative" things, like loading up the motor case as an
> antenna, loading up two fins (see the 'Fintenna' heading at
>          http://gag.com/rockets/airframes/YikStik3/
> for more details on that), and I'm currently building a 12" airframe
> that will have full dipoles on 70cm mounted just inside the skin as far
> From the 6" motor case as I can get them.  So many choices!  ;-)
>
> > Integrated antenna aside, my original search was for a unidirectional
> > antenna that I could connect to my computer sitting on my launch
> > prep-table, with the antenna affixed to one of my canopy legs on an
> > extension pole.  I would then use my 3 element yagi with my TeleBT and
> > my phone while watching and visually tracking from the launch line,
> > and just leave my computer running back at my prep table, to hopefully
> > capture the flight.  What is the best antenna for this application?
>
> The "problem" is that you want an antenna with good performance at high
> radiation angles (since the rocket will be "up" during much of the
> flight as seen from the flight line).  Many sophisticated ham radio
> antennas are explicitly designed to direct most energy to/from the
> horizon for longer distance comms and just don't work all that well for
> rockets in flight.  A simple 1/4 wave over a ground plane, a patch, or a
> quadrifilar helix on 70cm (or variants like the "Texas Potato Masher"
> are all pretty good choices.  An even better idea, but it can be harder
> to arrange, is to get someone to back a mile or so off from the flight
> line where they'll have a "broad side" view of the rocket through the
> entire flight... that's often the best way to get all the packets, since
> otherwise a ground station on the flight line is looking up at a
> sub-optimal antenna radiation angle for at least the boost and coast
> phases of the flight.
>
> In any case, just experiment!  The ground software shows received signal
> strength for each received packet, so you can easily see what works
> better and worse, and it's fun to try things!
>
> Above all, have fun!
>
> Bdale
>
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>


-- 
John D Sahr --- Seattle WA --- jdsahr at gmail.com
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