JDS,
Lucky students. I never got to do anything that interesting in
school. I've heard that quadrifilar helix antennas are hard to get
matched so congrats to your class for getting it to work.
One note. The TeleGPS is have is mounted in the nosecone clear of
everything else. In addition I have it mounted to a vertical piece of
copper clad PCB to try and give the antenna some minimal ground to work
against. I just bought a new longer nosecone for the rocket so that I
can increase the length of the PCB. I need to figure out how to
calculate the resonant frequency of the copper foil section. I'ts 1.5"
wide and 5 inches long currently. Can I calculate the resonant
frequency of that?
If I only had an antenna test range to do real measurements on instead
of guessing.
I did a flight last fall to 9600 feet with just the vertical for
tracking and it did a good job. Even though it was calm on the ground
the upper winds caught the rocket, even on drogue portion of the
descent, and it landed a mile and a half away. I had good data most of
the time and knew right where to go to get the rocket.
Terry
On 4/18/2016 7:49 PM, John Sahr wrote:
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 <[email protected]
<mailto:[email protected]>> wrote:
Web Customer <[email protected] <mailto:[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 <http://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 --- [email protected] <mailto:[email protected]>
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