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Thread: Antenna design for rocket telemetry

  1. #1

    Default Antenna design for rocket telemetry

    Hello HRF,

    First time post, so thank you and appreciation, ahead of time, to the moderators and old timers for your community.

    My son and I do a lot of high altitude amateur and experimental rocketry. Some of our launches go 50K+ feet and we support some university student groups that have launches > 100K feet.

    The past six months we've pivoted to building a radio telemetry system to track all aspects of the flight on the way up and down. This is arduino based and includes GPS, barometers, accelerometers, gyroscopes, temperature gauges, event detection, data logging to SD cards, and radio transmission back down to a base station, during all phases of the flight. We are using 2W serial TTL radios on the 70cm band (435.92 Mhz to be exact). At this point, we have everything working perfect, using a Yagi on the base station and testing with a half-wave inverted Vee antenna on the rocket rig. We did a local "mountain top to base" test and we are getting reliable data/telemetry transmission at 10 miles line of sight.

    So, we are now ready to test on some live rockets, but I am struggling with the antenna design for a small 3" diameter test rocket. I like the inverted Vee design we are using, but it won't fit inside the small 3" rocket. In our larger 8" and 10" rockets it won't be a problem, but for 3" I am struggling with options. Each leg of the half-wave inverted vee is about 6"ish (cut tuned to 1.01 swr) at a 45 degree angle. I could mount this on the outside of the rocket, but there would be a considerable amount of drag.

    A vertical dipole on the outside would be perfect, but the radiation pattern would be 90 degrees off at liftoff. Antennas are not my specialty, so I have been experimenting at long distances. Does anyone know how the radiation pattern and impedance would change on the inverted vee if it was mounted on the outside of the rocket, but the legs (at 45 degrees) were molded (curved) around backwards around the body of the rocket? Any other good suggestions for that 70cm frequency on a small 3" diameter rocket body?

    Thanks,

    Mike
    KK6EVH

  2. #2

    Join Date
    Oct 2009
    Location
    Oulu, Finland
    Posts
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    Default

    For satellite and space comms, both helical antenna and crossed dipoles are common.
    They offer directional gain and don't suffer from fading due to polarisation shifts.

    regards,

    Rob

  3. #3

    Default

    Maybe use 30 gauge magnet wire for the antenna? You could be finer than hair at 2 watts and could maybe be applied under the paint?

  4. #4

    Default

    @Tempstar, yes, that was my idea as well. A high gauge wire or even small copper tape on the outside of the rocket would be best, but I need a geometry that will work well on a 3" diameter rocket to test.

    Generally, the rocket goes straight up and at apogee it deploys a parachute that will put most of the airframe upside down for a while. So, I can't have a directional antenna pointing down, as it wouldn't be good immediately at launch or on descent. I really need an omnidirectional antenna

    A dipole will need to be mounted vertically on the outside, so it would have a weak spot pointing down and up -- not good when at high altitude. A J pole might be somewhat better and easy to mount vertically, but also has weak spots.

    I like the idea of the helix, but mounting on the outside and getting it tuned/sized right for a 3" rocket seems tough.

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