A quick bit of internet research threw up a few options:
- A mobile phone with GPS capabilities - Probably the most cheapest and readily available option. The phone can be set up to send you texts at regular intervals detailing its location. These texts only come through while the phone is in signal (texts will stop when it gets too high but will be sent again when in range). We ruled this one out pretty quickly as it is entirely dependent on the payload landing in an place with decent mobile phone signal. We live in a rural area so this is easier said than done. Furthermore, we will be hoping our payload lands in a nice empty field, avoiding built up areas - so again signal is potentially going to be limited. We are still toying with the idea of including a mobile phone in the payload as a backup but completely relying on one is a no-no for us. Another limitation is that the phone does not give you altitude information so you will never know just how high your balloon got on its journey.
- APRS tracker - Popular in the US but we quickly had to abandon this one as in the UK we are prohibited to transmit via amateur bands from an airborne vehicle. The idea is you create your tracking device and transmit your location over the APRS frequency. The network of receivers around the country will then hear your transmissions and pass on your location to internet servers where it's plotted on a map. Nice and easy, but we can't use it.
- Radio tracker - This is the preferred method of tracking high altitude balloons. You create a tracking device that is capable of receiving GPS signals and then sending that information over the radio using a frequency between 430MHz and 440MHz. This frequency band is unlicensed and is free to be used by amateurs both on the ground and in the air. The difference between this and the APRS is that you need to handle receiving the transmissions as well as sending them. We didn't really want to spend a lot of money on radio equipment, so when we came across this article it seemed to achieve what we wanted - receive the signal on a shoestring! The idea is that you can exploit USB TV dongles that usually plug into your computer and provide you with TV channels to instead receive a much wider frequency range - including 430MHz to 440MHz.
So we chose option three. We have started to buy the components and will update the blog when we have something good to share!
It's worth pointing out at this point that we did a LOT of reading of the UKHAS website. This is an excellent wiki site that is put together by people who are experts in this area. It is a highly recommended site to visit to get your project started.