High Altitude Ballooning – RTTY on 70cms

High Altitude Ballooning (HABbing) is one of my main hobbies. It involves launching a helium balloon with attached “payload“. The payload usually consists of a radio GPS tracker and a digital camera. It is enjoyed by a large group of enthusiasts. High altitude ballooning is a multi-skilled hobby which lets you explore the edge of space relatively cheaply – a basic flight can cost less than £200.

My Payload for NSE1’s Bicknacre flight booked for April 2013… Details to follow…

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It contains A home made GPS/RTTY tracker on 434.650MHz, a small “808” camera, and a GSM/GPS tracker. Listeners would be much appreciated as the balloon should be well in range around Essex.


If you are not interested in launching a balloon, a lot of fun can be had tracking them. There is a distributed listener system set up similar to APRS. It allows a multiple stations with their radios connected their computers to upload received telemetry strings to the internet. These strings contain the location of the balloon for tracking and other sensor readings such as pressure, temperature and altitude.

Once uploaded the information is displayed on the spacenear.us map.

hab flights


To join in with radio tracking you will need a 70cms rig capable of SSB and a computer connected to the internet. If you do not have a compatible rig, you can check out Pete’s great write up on SDR’s. They are perfect for this and are very affordable (<£20). Its exactly how I got started with HABbing but now I use a Yeasu FT-817, hooked up to my laptop running the dl-fldigi decoding software. SDR#’s audio output can be piped into the dl-fldigi software using “Stereo Mix” as a virtual input. A full write up on how to track along with a whole wealth of other information can be found on UKHAS.



The transmitters usually run on the license free ISM band, meaning they must be limited to 10mW. This sounds like nothing but when the balloons get high up you get a fantastic line of sight. RTTY at 50 baud is also very good at getting through on a weak signal. The record for furthest received string at 10mW is a whopping 800km!

SSDV is starting to be used to send back live digital images from on-board balloon webcams over RTTY. It is a little more tricky to decode as it uses a higher data rate (300-600 baud). The functionality for receiving this is built into dl-fldigi.


Daveake’s Raspberry Pi based TARDIS payload used SSDV to beam back this fantastic image!


If you are interested and fancy a chat with some fellow enthusiasts please drop by the IRC channel #highaltitude on irc.freenode.net, they are very friendly and knowledgeable!



12 thoughts on “High Altitude Ballooning – RTTY on 70cms

  1. I fear you may be infringing your Amateur Radio license.
    ‘It contains A home made GPS/RTTY tracker on 434.650MHz, a small “808″ camera, and a GSM/GPS tracker. Listeners would be much appreciated as the balloon should be well in range around Essex.’
    434.650MH?z is in the repeater input section of the band, and as per your license conditions:-
    ‘9(3) Without prejudice to Clause 1 of this Licence, the Licensee shall not establish or use the Radio Equipment in any Aircraft or other Airborne Vehicle.’?

    • Hi Lee,
      Thanks for the interest!
      The trackers use the 70cms “ISM” band but are limited at 10mw to comply with the ofcom license free ISM regulations (the same way you don’t need a license to operate wireless doorbells and car key fobs). However I do old a HAM license anyway.


      • As for repeaters, these modules would not be powerful enough to open a repeater unless you were within a few hundred meters. Also both ISM users and licensed HAM operators are both secondary user’s on the band.


  2. Even so, the license states that as an Amateur Radio license holder you ARE in breach of your conditions by transmitting from a balloon. Perhaps this needs clearing up with Ofcom?

      • Not a problem! We have a lot of worried HAMs asking up on this.
        As far as I know PMR’s are not allowed to be used un-manned and I think there is a maximum transmission length. My new trackers run on 434.300MHz @ 10mw ERP and can be used continuously and unmanned.
        Some more info on ISM can be found in the ofcom frequency allocation table here: http://bit.ly/14qHLt0
        434.04 – 434.79 at 10mw ERP falls under the “Licence exempt Short Range Devices” category. Making an Amateur license irrelevant for these purposes.
        Interestingly it seems to state “[Amateur] Users must accept interference from ISM users”


  3. hi I am ok on the rx side but where did you get the info for the tx side. I am looking into this to do a school project
    Steve G7AHP

    • Hi Steve,
      For the “TX” side I used an NTX2 transmitter on my first payload, this is probably your best starting point for HAB use as I think the RFM22b module is being phased out.
      Some info on how to drive the NTX2 can be found on the UKHAS site along with information on pretty much every aspect of the hobby! http://ukhas.org.uk/guides:linkingarduinotontx2


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