Rubber Duck Antenna
for High Altitude Balloon Use
April - 2011

We've had a few difficult recoveries when an exposed tracker antenna became damaged from entanglement with balloon remnants and parachute lines during descent and for the BEAR-7 and BEAR-8 flights I wanted an antenna that was small enough to fit inside the payload box and used a rubber duck that was installed on our tracker and simply dropped into the payload box with it.

I knew helical “rubber duck” antennas were terrible performers designed for short-range HT (hand-held transceiver) use where having a short, convenient, easy to carry antenna is more important than a better performing antenna. National Bureau of Standards tests show the typical rubber duck antenna has −5db gain compared to a -λ antenna held at face level and hanging a HT on one's belt can reduce signal strength up to 20db more which means a rubber duck on a 5W HT would only radiate ≈ 50mW.

But I also knew that some have used rubber duck antennas for HAB flights and figured they couldn't be any worse than the damaged antennas we had to deal with and that it was time to find out for myself just how good, or bad, they were for HAB use. We also follow and are seldom very far away from our payloads as we track them so I wasn't too concerned about not being able to receive tracker transmissions. In the end, the rubber duck we used worked fairly well, especially considering all the tin foil space suits that ended up being stuffed into the BEAR-7 payload box and were right against the antenna. However the ABE-1 flight we helped track and recover proved very different and only a few transmissions were ever received from the same tracker and rubber duck antenna. Luckily I decided to tie on a back-up tracker with a -λ antenna that hung below the main payload in a separate box and allowed us to track and recover everything. Two lessons were learned that day, don't rely on a rubber duck for HAB flights and that it was time to start using a back-up tracker on evey flight to help preserve our perfect recovery record.

A few more things to keep in mind if planning to use a helical rubber duck antenna for a HAB flight .

  • A helically-shortened rubber duck is a -λ antenna and, like all -λ antennas, requires a ground plain or some form of counterpoise to provide the missing second half of a -λ dipole. On a HT this is provided by the body  of the operator through capacitive coupling, but on a tracker in a foam box high above the earth a -λ length of wire connected to a point at ground potential on the tracker is required, like the shell of the antenna connector, to have a rubber duck function like a center-fed dipole antenna rather than an end-fed dummy load!
  • Some rubber duck antennas perform much better than others and which one will perform best on a particular piece of equipment and/or in a particular situation can only be determined by testing.

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