A Radiosonde Chase in Two Acts

It started when Mark Jessop sent me a message notifying me that there was a sonde down not far from where I work. The ill-fated RS41 launch RS_N3940146 reached an altitude of only 2083m before descending again. Unlike all the other sondes launched that day that ended up in far eastern Victoria this one came down comparatively close to the launch site.

An opportunity too good to pass up, I decided, after some encouragement from my colleagues, to “go out and get a coffee”. I grabbed my bike and went for a short ride to the landing zone. But a not so infrequent problem occurred…

Arriving, I spotted the unmistakable shape of a RS41 swinging from the upper branches of the tree, in a location way too high to retrieve. Giving up, I sent a photo via Slack and headed back.

In the afternoon, we received an email from a fellow sonde chaser known only by the name “The King of Foxes” - also defeated by its inconvenient location and asking for advice on how to retrieve it. Our answer was that we’d do the retrieving this time :)

Michael Wheeler was up for retrieving it after work - and not wanting to pass up on the opportunity I agreed.

Before I left the office, I checked Sondehub, which showed it was still there. Heading back there in the car and being “professional” sonde chasers (hey, we’ve been paid to do it twice, that counts right?) we returned, armed with the correct equipment.

Tuning the Icom 7100 into the frequency showed it was still there. Surprisingly for something only transmitting 25mW, we could hear it from a very long way away when monitoring for a carrier in CW mode (way easier to hear than looking for it in FM mode). Given that we were well beyond the 8.5 hour burst kill timer I was surprised to hear it - but maybe there’s a minimum altitude requirement before burst kill is activated?

(yes, the time’s set wrong. I’ve fixed that now.)

Using a Spiderbeam HD 12m Fibreglass Pole with an EDC Rope Cutter duct-taped to the end of it, we attempted retrieval.

Hooking the rope cutter around the string and pulling freed the sonde which then unfortunately directly hit the line of rocks on the edge of the roundabout. If I’d pulled it back just a little further, it would have landed nicely on the grass. They are pretty tough, fortunately - although there was that one time

Safety note: if you’re going to do this, be very aware of where the nearby power lines are and do not use a conductive pole (metal or carbon fibre)!

Another successful chase - only had most of the work day in the middle…