UBSEDS25 balloon has Slow Scan Digital Video

UBSEDS18 Solar Powered Balloon

Bristol students plan to transmit 434 MHz Slow Scan Digital Video (SSDV) from the UBSEDS25 solar powered high altitude balloon planned to launch on Saturday, July 1.

On the UKHAS Google Group Richard Meadows M0SBU from University of Bristol Students for the Exploration and Development of Space (UBSEDS) writes:

We’re planning a launch from Bristol this Saturday, July 1 between 0500 and 0530 BST. This is weather permitting, but the forecast currently looks okay.

This flight is similar to the previous UBSEDS24, except with some bug fixes and adjustments. It’s using a 1.9m envelope and longer payload train, and so there’s a NOTAM in place. This tracker has a Raspberry Pi Zero V1.3 attached, which transmits images when solar power is available. It’s a different design to our launch last August; in this case the tracker will continue to operate even if the pi fails. For the curious the ‘pi status’ telemetry values are: 0 = off, 1 = on, 2 = PITS started, 3 = SSDV started).

There will hopefully be a cutdown mounted between the balloon and the tracker. We’ll be testing the 434MHz uplink whilst it’s still in range of Bristol; if it returns over the UK at a convenient time and place we will attempt to trigger the cutdown.

The tracker has a variety of transmissions:

• 434.635 MHz USB Telemetry:
– Contestia 16/1000 with pips and RSID, transmitting telemetry. Once per minute below 8km altitude and every two minutes otherwise.

• 434.637.5 MHz SSDV:
– Usually 300 baud RTTY, 850Hz shift, 8N2.
– GMSK within 100km of Bristol and Farnham as marked on the attached map:
– GMSK at 12 ksymbol/s. 4×4 interleaved, R=1/2 convolutional K=5, HDLC framing, whitened etc as per the AX5043 manual. Concatenated with RS(255,223) to mop up some burst errors.

If you are listening to the RTTY, remember to turn off the ‘RxID’ button on the top right of dl-fldigi.

Rather than the usual JPEG SSDV, this is transmitting Better Portable Graphics (BPG) images. This is experimental, and doesn’t support it just yet. Hence receivers should instead upload to

Please read the instructions on this site. You’ll need dl-fldigi release 3.2, as explained on the site. The dl-fldigi release can be found here:

The flight is expected to head south-east towards France. Many thanks to everyone who attempts to track this.

Richard Meadows M0SBU
Bristol SEDS

Launch date/times are always subject to last-minute changes, check the UKHAS Google Group for updates.

Useful High Altitude Balloon links for tracking etc