After the talk last night I took a moment to mention my friend Sam Sully, who is running a club at Monmouth School to launch 8 High Altitude Balloon’s (HAB) into the upper atmosphere. The club is involving 42 students from the ages of 12-18 who have been working in teams to build payloads for their balloons.
The payloads used by the club are based around a Raspberry Pi Zero single board computer, Raspberry Pi Camera V2, Radiometrix UHF transmitters (each payload on a different frequency between 434.0MHz and 434.8MHz) and GPS Module. The raspberry pi is responsible for getting the location of the balloon from the GPS and sending the coordinates over the radio using the RTTY protocol.
There are a few ways of receiving the radio down-link from the balloons. The easiest method for radio amateurs is to use either a 70cm radio with a computer interface or a software defined radio, such as an RTLSDR dongle which many of the club members already have.
In terms of antennas, the clear line of sight provides a relatively easy job. For a tracking vehicle a standard mag-mount 70cm mobile antenna will be sufficient, or even a 1/4 wave ground plane ghetto mounted to the roof of your car! For a base station a high gain 70cm yagi would be more suitable to get better range and pick up the balloon from lower altitudes.
A simple ground plane antenna made from some stripped-back RG-117 strengthened with straws. Works a treat!
An 868MHz antenna built from welding rods and 25mm^2 trunking (this was used for experimental 2-way comms with the balloon and not for tracking)
In order to decode the packets from the balloon, the following software is required:
- SDR# – The first piece of software that I used is called SDR# (SDR-Sharp). It is used to control a SDR dongle, and tune into the frequency transmitted by the balloon payliads. A full guide to installing and setting up the software can be found in one of my previous posts. Download Link
- VB-Cable – This is a virtual audio cable, used to send the audio from SDR# to the packet decoding software. Download Link
- DL-FLDIGI – This is the software that decodes the RTTY packets. Download Link
First of all you need to download and install SDR#. Clear instructions on how to do this are provided here
Then you need to set up VB-Cable to send the audio output of SDR# to the RTTY Decoder.
- Download VB-Cable from the above link
- Extract the .zip file
- Run “VBCABLE_Setup_x64.exe” as an administrator (don’t use x64 version if you are using 32bit windows)
- Click on “Install Driver”
- Accept the unverified driver warning
- Restart when prompted
- Go into the sound settings (right click on volume icon, click “sound”)
- Click on “CABLE Input”, and click on “Set Default”
Now that the virtual audio cable is setup, you will need to is set up SDR#. Tune the radio to the frequency of the payload you plan to receive (these will be posted at a later date), and set the mode to USB. You can adjust the squelch control but that is not required. Set the bandwidth to around 10khz.
Now, your SDR# window should look something like this (except tuned into the 70cm band):
Finally, open dl-fldigi (HAB Mode), which decodes the RTTY packets.
You will need to do several things:
- Select the appropriate audio input (“Virtual Audio Cable” or “CABLE Input“)
- Move the red markers until they are overlapping the two RTTY signals. After you have done this once the software will automatically track the signals.
- Select “Op Mode” from the toolbar at the top, then hover over “RTTY” and click “Custom“
In this window you must alter these settings:
Carrier Shift => Custom
Custom Shift => 450
Baud Rate => 75
Bits per character => 8 (ascii)
Parity => none
Stop bits => 2
Now go into the “Configure” menu and setup your callsign. This will be displayed on tracker.habhub.org with every upload you submit.
Now the software is setup you should now see text on your screen. dl-fldigi parses this data and uploads it to habhub. Well done you are now contributing to the tracking!
Tracking a balloon
Now that you are picking up telemetry, the habhub tracker will predict the flight path and landing site for the balloon. The chase vehicles will try and get to the landing site to recover the balloon. Please note this is not as easy as it sounds and takes some practice! Laptops are essential and a minimum of two people per vehicle is recommended.
I hope this is an informative article and perhaps enlightens some of you to the world of high altitude ballooning. Please check out https://ukhas.org.uk/ which will have some better instructions on it to help get you set up. If you are having issues don’t hesitate to comment below or send me an email.
Hopefully we’ll see some of you at the launch next weekend! I’ll let everyone know on Wednesday which day we’ll be launching.
-Peter Barnes (2E0UAR)
(edit: i’m sorry everyone I clearly can’t spell balloon)