This article documents measurement of a prototype two element Yagi for Fox Hunting / portable direction finding: Prototype 2el Yagi for 401MHz (Radiosonde) Fox Hunting . See the original article for the design criteria.
Prototype 2el Yagi for 401MHz (Radiosonde) Fox Hunting – measurement showed a prototype and measurements.
Above, the antenna with MySondy custom firmware for a TTGO.
In Bruce’s own words…
This morning over breakfast I had a look at the Sondehub website. Weather radiosondes are launched daily from Brisbane Airport and I have a receiving station at home (Toowoomba).
Today’s radiosonde (16/12/24) tracked west towards Mt Glorious which is unusual as they normally go to the east and end up in the sea. Sondehub gives a prediction of the expected landing site and its generally quite accurate. It was expected to land about 10km west of the town of Esk, not far north of here. This area is very hilly and heavily wooded.
We packed the car with a 400MHz receiver and MySondy tracker with the two element Yagi antenna, and set off. The map indicated a 58km run. My wife Liz is the tracker and navigator.
We headed to a high location about half way to the landing point, and stopped to do some navigation.
Above is a screenshot of the Sondehub tracking site.
This gave us a Lat/Lon for the radiosonde which was still at an altitude of 14,000m and travelling at 55km/hr. The radiosonde had already burst and was descending rapidly. The landing site had changed by only a few hundred metres from the original. We had 14km to go so we set off.
About 2 minutes later the signal vanished completely. I was concerned the radiosonde transmitter had failed as it stopped abruptly but we continued on. About 8km later we received a very weak signal and I knew it was still running, Yippee! We had to go past the radiosonde location and turn back on a dirt road to the south east to get close to the radiosonde. The signal couldn’t be heard here and we were about 5km from the previously recorded Lat/Lon. We continued on and at 2.1km distance from the radiosonde we started to receive the signal. Not sufficient strength to decode the exact position. Further along the track (1000m from radiosonde) the signal increased and we could log the reported position. I stopped the car at the closest location (~200m) and ventured into the heavy vegetation. The bush was choked with Lantana and it took 20 minutes to cover the 200m.
I am using a MySondy GO radiosonde tracker, which shows the location of the radiosonde as well as your own location, and the distance and the bearing to get there (an excellent device).
When it indicated there was 19m to go I started to look for it and was concentrating on looking at the tree tops. I could see nothing! I moved forward till it was 2m away and there it was in front of me at my feet.
It was sitting upright with its antenna flat on the ground, this accounts for the fact I could not hear it for more than 1.5km.
I arrived back at the car bleeding from about minor cuts and lacerations from the journey, but it was worth it to succeed.