May 2010

Radio Direction Finding (Fox Hunting)

Finding BOM Balloons, for a while a couple of AREG members have been chasing digial radio sonds that are launched twice a day by BOM (Bureau of Meteorology). Just recently the BOM balloons have gone back to the analog ones. This just makes it harder to track but as much fun as all ways.

Adrian VK5ZSN has been working on and off for the last 5 years, to get all this working. On the way Matt (VK5ZMC) VK5ZM, Scott VK5TST, Peter VK5TZX & Adrian VK5ZBR have all contributed during the project. Still not finished but I am confident that as long as an emitter may be received, we can locate it.
The current activity is to help Terry out with his balloon project. More details at http://projecthorus.org/ on the first test hunt with Adrian new set up, Terry successfully found the sonde with nil experience in RDF.
I am looking forward to the launch of the payload in January.

Last year, while BOM were using the Digital Sondes, Adrian has lots of fun in chasing BOM sounding balloons, and has recovered many of them in the past. Adrian's RDF setup - a Toyota Land Cruiser kitted out with an amazing array of radio's, computers & custom electronics that Adrian has put together with help from a number of members of AREG. At the heart of the setup is Adrian's radio direction finder module - a system that Adrian came up with some time ago, it interfaces with both a rotating beam yagi antenna, and performs Doppler based direction finding. The Doppler array (4 1/4waves on the truck roof) is able to give an instantaneous bearing to a radio source without requiring manual input. The output from the system is plotted to a GPS tracked map, to triangulate the location of the source.

Adrian’s RDF truck

To demonstrate the system to Terry and show him that we could find his payload after the balloon flight, Adrian took him out to chase one of the 2 daily BOM balloons. Predictions run with the CUSF flight predictor suggested that the balloon would land somewhere near Sedan, a manageable distance from Adelaide. Our BOM primarily launches analogue radiosondes (Vaisala RS92K) - these 'sondes do not include GPS receivers, they are tracked by ground based radar. This meant we wouldn't be able to track the Sonde's course by GPS, the only way to locate the 'sonde is via RDF techniques.

Adrian and Terry headed out towards Sedan hill, so that we would have a good vantage point & be able to track the 'sonde as it came down. No problems up until this point - I was operating the RDF equipment, after a short while spent learning to work everything, I was confident that we had a good idea of where the balloon was. However, we'd forgotten to start the radiosonde decoding software at the beginning of the flight, and due to the very limited information broadcast by the analogue 'sonde in question, we didn't know if the balloon was still ascending, or if it had started to descend.

A short while after we arrived at Sedan hill, the signal faded, then abruptly disappeared. Unsure if the 'sonde had landed or if it had failed, we set off down the last vector we'd plotted. 10 minutes later, we still hadn't heard the signal, until we passed a field & I heard one of the radios in the truck pick it back up again - but this time on a totally different frequency! It looks as though the bump on inpact had upset the analogue radiosonde's crude transmitter (adjusted with trimpots by the looks of things) & shifted its frequency. A short while & a few vectors later, we were quite confident we'd found it.

This shows that even someone that has no RDF experiance like Terry can find a fox easily. All you need is a bit of equipment.

Map showing the location of the downed balloon.

Below a picture of Terry with balloon in hand.

 

A few more photos of the RDF truck & balloon below:

 

Adrian's RDF truck	Adrian's RDF truck	Adrian's RDF truck
At the controls		Driver Seat
DF System Block Diagram	DF Unit
Beam Pole on Window	Bust Balloon	BOM Radiosonde
Radar Reflector	Analogue (left) & Digital (Right) Sondes

 

More information and updates soon, Adrian VK5ZSN

 

 

 

 

 

 

 

 

 

 

 

Page updated on 27 May 2010