There are a couple of risks with a project like this, landing in trees, water or landing somewhere where there is no GSM coverage. The best way to minimise these risks are to use a balloon trajectory predictor, we used this one:

http://www.srcf.ucam.org/~cuspaceflight/predict/

It was only 5km out for us and likely would have been closer if I didn’t over inflate the balloon. The trick is to use that predictor and adjust your launch location so that you will land somewhere where there is coverage. Additionally somewhere that is not forest either!

The GSM tracker used was the TK102 from Xexun, this is a very good unti, alas there are many clones of it around so I bought the one used direct from the factory.

The SPOT messenger would likely work well but I would worry about putting something that expensive in a balloon just in case. It means you do have a good chance of finding it as coverage would not be an issue but tall trees or a lake might mean and expensive experiement.

We are trying do something similar for a science experiment but we don’t know what GSM / GPS tracker we should use (we want minimum cost so that we can repeat the experiment). The other issue is that it is not clear to us if this will work outside metropolitan regions where GSM coverage is quite limited.

http://www.gsmworld.com/cgi-bin/ni_map.pl?x=7&y=2&z=2&cc=au&net=te

The other option we are considering is a SPOT Messenger tracker (http://au.findmespot.com/en/) but is quite expensive ($~400 including 1yr subscription)

We are located in Canberra.

Hope you can guide us.

Thanks,

http://www.sparkfun.com/commerce/product_info.php?products_id=9143

The key thing is to mount them in the horizon polarisation rather than vertical as of course as the nulls are at the ends od the antennas and the balloon is right above.

There’s a few 3 and 5 dBi antennas around, but if 2 dBi is enough I’ll go with that.

I was hoping to find out what gain your antennas have? I take it you’re talking about the “rubber duck” type omni antennas?

Thanks