VHF antennae for rockets?

Discussion in 'Rocketry Electronics and Software' started by Micro-Trak, Feb 13, 2019.

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  1. Feb 13, 2019 #1

    Micro-Trak

    Micro-Trak

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    We released a new tracking transmitter ( The MT-2001, http://byonics.com/microtrak) primarily for high altitude balloons and Drones) this year. Its a VHF, Ham Radio 2 Meter band, frequency agile transmitter with a maximum of two Watts output. The transmitter itself is 1 X 2 inches, so it seems like it might be suitable for rockets as well. My question is, what are you using for VHF antennae in high-powered rockets, if anything? Would a UHF version, working outside the "normal" APRS system suit rocketry better, since the antenna is not as ungainly ( Pun intended, for those fans of A.G. Bell and the dB) as a compromise VHF antenna. Since range with VHF transmitters versus UHF transmitters have a range nominally 6 times further, I have shied away from doing a UHF tracker or "Fox" ( Simple RDF transmitter) but I can see that a 1 meter long antenna may be a bit too much to accommodate. Your thoughts would be very welcome on this.
     
  2. Feb 13, 2019 #2

    jrkennedy2

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    Another reason I NEED to get my Technician's License...

    That looks fun!
     
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  3. Feb 14, 2019 #3

    UhClem

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    The tiny antenna on an Alinco DJ-C5 worked for me. But I prefer to operate at 70cm and avoid flooding digipeaters over a wide area.
     
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  4. Feb 14, 2019 #4

    FMarvinS

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    I currently enjoy & use the MT-2000 connected to a GPS5HA Module and open logger in 2.5 inch and larger diameter rockets for GPS tracking. Due to the 2 watt output, I keep it on a sled within the nose cone some distance from the altimeters. Since I also use a 70 cm tracker, I often use an Opek HK601 VU 2meter/70 cm HT style antenna (7.5 inch length with a VSWR < 2.0) within the nose cone for either 2 meter or 70 cm transmitters. If a smaller nose cone is used , then I use a smaller, more compromised, dual band helical HT antenna mounted on the nose cone bulkhead extending several inches into the payload bay. I've had good success with both set ups.

    I've reviewed the specs on the MT 2001 and do plan to purchase one for smaller diameter rockets-particularly MD and 2 stage ones planned for high altitude flights. With its 1 inch width, it may fit in a 38 mm AV bay and definitely a 54 mm one.

    With respect to 70 cm transmitters, as you know there are several models used for RDF and GPS purposes. Since most sport rocketry launches are < 20,000 feet, LOS 70cm transmission with a 250 mw or higher output transmitter is probably more than adequate. The successfful tracking of rockets reaching altitudes of 18, 000+ feet using 100 mw to 250 mw 900 MHz transmitters have not infrequently been reported.
    The antenna question is one of room or space. An HT style 19 inch 1/4 wave length 2 meter antenna would be more appropriate on the HT receiver on the ground and not within the rocket. Most utilize smaller, less efficient antennas due to space limitations.

    Fred, L2
    ICBM, Camden, S.C.
    KG4YGP
     
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  5. Feb 14, 2019 #5

    FMarvinS

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    edited to avoid message duplication
     
  6. Feb 14, 2019 #6

    DaveW6DPS

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    I have used a Tiny Track 3 in rockets in the past. I am thinking of using it again on a large project I am planning. This would be a GPS module, the TT3, and probably a Bao Feng HT. I have also considered using your MT-2001.

    Mostly we use 70cm rather than 2 meters. This partly because of the smaller antenna needed in the rocket. This is a general rule, and there is certainly no reason we couldn't use 2 meters.

    One thing to remember is that omni-directional coverage is important, and normally vertically polarized.

    I used a 70cm roll-up J-Pole in the past, but usually use a coaxial dipole now. I put the antenna in the body tube below the electronics bay, so my altimeter is exposed to as little RF energy as practical.

    With a 2 watt transmitter, a rubber ducky should be quite adequate or 2 meters. For most rocket flights, the altitude and range is not that far. A few high-altitude launches may go above 25,000 feet above ground level, and drift 8 to 10 miles away. Higher or farther would be rare.

    Note that with higher/farther flights recovery involves driving, and a typical mobile installation includes a higher gain antenna than the more routine flights where we use an HT with rubber-ducky. I use a Kenwood HT for tracking "local" flights, and a Yaesu FTM-100D with a 3/4.5 dbi gain dual band antenna on my vehicle for longer recovery, like at Black Rock.

    Current APRS units marketed for rocketry, Big Red Bee for example, tend to be 70cm with 100mW output. With a 2 meter tracker with 2 watts out, a more modest antenna in the rocket would be fine.
     
  7. Feb 14, 2019 #7

    DaveW6DPS

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    Also, 70cm is more popular in my experience, and avoid the "normal" APRS system on 144.39, since we use the tracker for telemetry in many cases and often use beacon rates of 5 or 10 seconds.

    For future reference, telemetry inputs would be helpful to some of us, such as Dallas 1-wire for temperature, and analog and/or digital inputs for telemetry/event data.
     
  8. Feb 14, 2019 #8

    FMarvinS

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    Dave-I agree Telemetry added would be a good enhancement. I'd be interested in a baro-receptor based altitude message (?every 5 seconds) with GPS NMEA transmissions. Since the Byonics MT transmitters are not "fixed frequency," on the two I have, the frequency was set for unused APRS transmissions in the USA such as 144.800 MHz.

    Fred
     
  9. Feb 15, 2019 #9

    UhClem

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    Linear polarization with direction determined by orientation of the antenna. Which varies during flight so circular polarization on the ground end is a big help.
     
  10. Feb 15, 2019 #10

    Charles_McG

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    6m band. Build bigger rockets.
     

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