Balloon-borne antenna for field day.
This year we setup a balloon lofted 160 meter 1/4 wave antenna. We used a 300 gram weather balloon to loft the antenna which was made from 22 AWG bare copper wire. The balloon was tied in a three points using trot line for two and the wire for the other. We had issues with the wire flopping around near the feed point so we used a insulated electric fence post to hold it 4 ft off the ground. We also tied a smaller balloon about 20 ft up from the feed point to provide a pivot point so the wire wouldn’t flop down to the ground as much. In the pictures the radial was laying over about 30 deg but later in the evening we got it up to 65 deg by moving the anchor points and letting out more trot line.
We fed the antenna straight from a 50 ohm coax with a BNC to banana plug adapter. To ground the antenna and provide counterpoise we just connected it to a long metal fence which provided both a good ground and a very long counterpoise. I wound a static discharge choke 50 turns on a FT-240 type 43 toroid that gave about 2 mH and provided a very high impedance at HF but was very low resistance at DC to discharge any static on the antenna.
The antenna had a 1.6:1 SWR on 160 m and we could easily tune the antenna from 80 m-20 m. It was quite a surprise it worked so well on 80 m being an end fed 1/2 wave fed from 50 ohm coax. In theory end fed 1/2 wave antennas are very high impedance but in this case the tuner tuned it very easily. I should have taken more measurements but we got busy operating and forgot.
This website showed us how to properly tie the base of the weather balloon so that the latex wouldn’t rip. http://www.highaltitudescience.com/pages/tying-off-a-weather-balloon
Please use a static choke and watch the weather very close you don’t want a long highly conductive wire trailing up towards the base of a thunderstorm!
Here are some pictures of the setup.