Web Customer <[email protected]> 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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