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After decades of silence, a vintage spacecraft says hello to Earth

ISEE-3-promo ISEE-3 and sample GNU Radio GUI

This was the headline in 2014 when a small group of engineers began communicating with a 36-year-old space probe. The Planetary Society details the fascinating story of how modern communications systems recreated the complex control systems needed to control the ISEE-3 as it returned to our planet Earth.Known as the ISEE-3 re-boot it beautifully illustrates how communications equipment design has changed. This small group of mainly software engineers re-built the functionality of rackful's of equipment with an open-source software package GNU Radio and a small SDR hardware package. The teams YouTube video is well worth a watch.

GNU Radio is an extremely powerful set of software and has been used to build complex communications systems. The latest example was testing the recently renovated Apollo 10 lunar communications. It also plays an important role in backwards engineering proprietary standards including LoRa. Matt Knight presented this work at GRCon in 2016.

Looking at what is currently available and the quantity of publications about SDR in the Amateur Radio community it is hard not to come to the conclusion its popularity peaked a few years ago. No new software packages have emerged and many of those that did have been acquired by commercial manufactures and become proprietary to specific hardware. I am not sure why this is, the complexity of building systems might be a factor, it is relatively easy to use a low-cost USB dongle to listen but a lot harder to include the necessary bandpass filters for good reception and make the transmitters work cleanly. After searching I find many projects abandoned after getting really interesting prototypes working, presumably their originators ran out of interest or could not attract a wider audience.

I am experimenting with one open approach. The Analog Devices ADALM-PLUTO SDR is a relatively cheap $250 hardware board which can provide duplex TX/RX between 70 MHz to 6,000 MHz with 56 MHz bandwidth (needs a "hack" to cover that full range). The platform is not perfect, it was only built as a manufactures test aid, but with a few modifications it becomes a capable SDR base. Through various software projects it has become a staple in the education world and is popular with Amateurs worldwide. It makes a great Amateur TV transceiver, a VHF/UHF all mode transceiver, and after a Google you will see many active projects.

My ultimate interest in the Pluto-SDR with GNU Radio is the creation of a set of standard configurations which will meet the limits of the various License conditions for digital transmissions on the VHF-SHF bands. This would allow an experimenter a relatively low cost entry point for exploring digital point to point in their locations. Ultimately this approach would not be as cost effective as a dedicated hardware solution such as Project NPR-H, but as a proof of concept, perfect.

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Thursday, 29 September 2022