VHF End-Fed Half-Wave Dipole
Antenna Construction
May - 2006

This is the impedance matching transmission line portion of the APRS antenna built and used for SABLE-1 & SABLE-2.
The feed line is to the left and the first few inches of the half-wave radiating element can be seen on the right.

The APRS Tracker for SABLE-1 required an antenna and it was tempting to simply attach a small rubber duck type antenna directly to the tracker that would allow both to fit in the payload container. But rubber duck (or normal mode helical) antennas make a very poor antenna and are good for little else then what they are intended for, which is short range hand held radio use where their small size is more important then performance. Rubber duck type antennas also require a ground plain or some other type of ground reference to operate properly, like the body of the person holding the radio it is being used on, but there is no ground reference available in a styrofoam container high above the earth.

The ideal antenna for balloon use is a half-wave antenna, as no ground reference is required, and the center-fed antennas built for the BEAR project were excellent. However the feed line connection point makes vertical use of a center-fed antenna difficult on a balloon package, so I searched the web for info, borrowed an antenna analyser, and proceeded to try and build a half-wave end-fed antenna that could be simply hung vertically below the payload container and would hopefully work as well as my previous center fed antennas.

August - 2007

Note: this page WAS and I planned to write more about my antenna building experience and the construction of the two end fed antennas that were completed, but this is unlikely with so many projects, little time, and now wanting to develope smaller and lighter antennas for balloon use.

There are no construction photos, but a few were taken while the antennas were being tested and

this is the first antenna that was made, the prototype for the one seen at the top of this page, and the antenna used for SABLE-3. It may not look that great, but it works very well and SABLE-3's 300mW APRS signal was received over 600 km away.