Interesting. interesting. I'm probably jumping the gun here but I'm curious - are you getting any trends on types of biologgers or specific manufacturers people are talking about? Or is everyone using different tags/manufacturers? 

Ah! It's great to find out about your tags - great video, thanks for sharing. We'd love to hear from some of your users about their experiences with your tags! Would you be able to share the poll with your user community? 

Hey Stephanie,

Thanks a lot! Sorry I missed your message but of course I can ask our users about their experience with sensors!

Makes sense if you have the cash...

You are most welcome! You would have to either have them custom make collars to fit hyenas OR DIY by fitting the Milsar GSM devices to collars of your own liking - but I guess you also prefer to have drop-offs - something the Milsars do not have!

You are welcome! An alternative would be to look into the GSM options from Africa Wildlife Tracking (https://awt.co.za/product). I have no personal expereince with them at all but they are likely to have experience with hyena collars.

BTW. The internal drop-off option in the Vectronic-Aerospace collars is super reliable.

Hi Lars,

One of the problems you identified with your Milsar units was the antenna being worn off. This was solved in our units by the antenna being epoxied into an abrasion resistant heavy plastic (a single piece that was also the mount and provided extra protection on the ends). I'd still want to add more of this material around the edges of the solar panels on a hyena, but for what it is worth I tried one of the koala units on our 17 kg dog for a month or so and it didn't seem to take any worse wear than it did on the koala. Any solar GPS system is going to need a counter weight to keep the GPS and solar panels skyward, so that is where I would incorporate a release mechanism (should one be required). 

If you can find a radio amateur club in your area, they could be a good resource.  They have a competitive event called fox hunting, which involves locating a hidden transmitter.

Anyway, a directional antenna for 401MHz can be made easily and cheaply but you have to know what you're doing.  The cheapest (USD20?) radio receiver is an SDR dongle for your laptop or Android phone, but again you have to know what you're doing.

Using this setup would be like tracking a VHF animal tag, you swing the antenna around until you get the strongest signal and go that way.  It would not be like using the Argos CLS, you don't get a GPS location of the tag, and it doesn't identify any tags it picks up.

1/ A goniometer is a type of receiver which can measure an angle and then tell you where your signal is coming from in a specific frequency band. It is much more complicated to develop which explain price.

2/ With a basic receiver using a YAGI antenna, you will have to get the signal location by turning around. If the receiver is not enough sensitive and if the antenna is a bad quality, you won't get signal at all. You can lose lots of time.

3/ With a basic receiver using an omni-directional antenna, you will get the signal but you won't know where the signal is coming from. Same as before, if the receiver is not enough sensitive and if the antenna is a bad quality, you won't get signal at all. Depend what you are looking for.

I hope this will help you to better understand differences between these tech. 

If you need more informations, you can contact me directly by mail at virginie.perilhon@xerius.fr

The CLS Goniometer is an excellent tool for the job - I believe it is also available to rent (at least it used to). 

If you want to go the low-budget route I would consider building a cross antenna with 4 yagi's, connect these to some kind of 4-channel receiver, and use the relative differences in intensity between the orthogonal directions to estimate the angle of arrival. You would need a way to simultaneously change the Rx gain on the four channels. Remember the transmission rate much lower than a typical VHF transmitter so it will take a while to find a tag this way. Using a single yagi would be basically impossible unless the sea is a mirror and the tag not moving in the waves.