Fox / Sonde hunting

sonde7After 3 previous day time successful sonde recoveries, Peter VK5PE  and myself Ivan VK5HS thought we would attempt a night time sonde hunt using the chase car software. This was the first time I had used the software and Peters first attempt at a recovery.  I had been using a home brew 5 element yagi with a R10 Icom receiver, which can be seen in the below picture along with a phone antenna used for internet access in the vehicle, the old chassis houses the raspberry pi, RTL-SDR and antenna switch.  A quarter wave vertical and a home brew crossed dipole, is some of my other equipment I use.

sonde1

I decided to make a new directional antenna. After some research on the net,I decided on the HB9CV design. http://www.qsl.net/dk7zb/HB9CV/Details-HB9CV.htm   There is also a handy online calculator,https://www.changpuak.ch/electronics/HB9CV.phpWith the dimensions from the calculator I set about sourcing the necessary components all from the junk box.Some 10mm alloy tubing for the boom, a couple of stainless steel tapered whip sections which were off cuts from commercial whips, and a wire joiner terminal strip. I removed the brass wire joiners from the plastic housing and cut them in halves, a small screw and eye terminal for the coax ground.I drilled the boom as required by the plans.

sonde6 The element holes were drilled  to 1.5mm. The tapered elements are then tapped into position until they locked tight into the boom, the elements start at 1.2mm and finish at 2mm.  I then constructed the matching section from another off cut of whip.

Next I installed the matching section using heat shrink to lock the screws into place. Then the variable capacitor was installed to aid in tuning the antenna.

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sonde4

I made up a coax to suit and then tuned the antenna for 402.00 MHz.

sonde2

The next test was to see if I could hear the sonde signals from Renmark, I started with listening for the Adelaide sonde which was a good signal at approx 6000m. Next I listened for the Melbourne sonde which I received with good signals at approx 20,000m. Then a test to compare front to back and vertical and horizontal polarization. All appears to work as I had hoped, now to wait for a sonde to travel towards the Riverland so the real test can be conducted. And yes we were successful in recovering our first night sonde.

I hope you enjoyed this article.  Ivan VK5HS.

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