Sunday 27 August 2017

868MHz LoRa HAB Tracking Success

Most HAB (High Altitude Balloon) tracking in the UK involves the use of 434MHz ISM devices due to the ready availability of suitable antenna and receiver equipment due to it sharing the 70cm amateur radio bands.

868MHz ISM devices are available but are not as widely used. Back in December I posted about trying to track a flight by HAB Enthusiast Dave Akerman who is experimenting using LoRa devices on this band. I had limited success receiving that flight and another ones so when I saw that Dave was planning another flight today using 868MHz LoRa I had a rethink on how to approach tracking it.

The antenna I used was a collinear one built from cheap satellite coax, similar to that I built for ADB-S however rather than having a long coax run to the LoRa gateway I opted to put the Raspberry Pi up on the pole at the base of the antenna to limit any loss.

The antenna can be seen connected to the Raspberry Pi and LoRa add on board, the Pi has a WiFi dongle.


The antenna was inserted into a piece of conduit to keep it upright and it and the Pi were strapped to a 5m painters pole (using a plastic lid as an insulator)


A USB power pack was also strapped to the pole to keep the Pi powered, hopefully you can see it in the photo below.


The pole was put up and was about the same height as my normal dual band collinear


Well it all worked extremely well, and got a lot of decodes as can be seen by the pie-chart generated by the habitat.habhub.org system, the third best receiver only bettered by Dave himself (M0RPI) and a station nearer to the flight path.

You can see my geographical position relative to the flight below (I am the station NNE with the green line, about 160km away) and received a lot of telemetry strings even when the height of the balloon meant I was outside the 5 degree above the horizon circle (shown in green).


The Pi was connected to my network via WiFi and controlled by a Putty console on my shack PC


It was a useful experiment and I am thinking of installing a dedicated mast mounted LoRa receiver with 868 and 434MHz antennas (and possibly pre-amps and filters) following this result.

Monday 14 August 2017

Shortwave Radiogram

In March 2013 The Voice of America (VOA) started an experiment called the VOA Radiogram which transmitted digital text and images using the powerful 50 year old analog shortwave broadcast transmitter at the Edward R. Murrow Transmitting Station near Greenville, North Carolina.

The idea was anyone could receive the radiogram on any shortwave radio, even an inexpensive portable one with no SSB capability. By feeding the audio from the radio to a computer, either by a audio lead or even using the a microphone the listener could decode the text and images using simple software.

I had seen mention and reports on social media of people receiving them but somehow never got around to trying it myself.

VOA ended the experiment back in June this year a week before the retirement of the program producer Dr. Kim Andrew Elliott.  An offer to continue the broadcasts on a contract basis was declined, so a follow-on show called Shortwave Radiogram began transmission from the WRMI Radio Miami International transmitting site in Okeechobee, Florida and Space Line in Bulgaria.

The Shortwave Radiogram transmission schedule is (at the time of writing and all times UTC)
Saturday 1600-1630 9400 kHz
Sunday 0600-0630 7730 kHz
Sunday 2030-2100 11580 kHz
Sunday 2330-2400 11580 kHz
All via WRMI except for 9400 kHz, which is via Space Line in Bulgaria.

I spotted a tweet a few weeks back (can't remember who from) mentioning the @SWRadiogram so my interest was piqued, I wasn't around for this weekends Saturday transmission in Europe but had a go on Sunday for the one from America. I wasn't expecting great things due to the levels of noise and poor conditions of late.

I have the decoding program FLdigi already installed on my computer for other datamodes and for information on how to decode the radiograms (sent using MFSK32) visit this page

On the 0600UTC transmission I managed just one poor image


 but during the Sunday 2030UTC transmission I got four decent images, the fifth was lost to QRM





I also made two short videos (on hand held mobile phone so a bit shaky) which show the incoming text and images.