I’ve been working on my system for receiving signals from deep-space spacecraft since the summer of 2019 when KC2TDS and I built an X-band circular polarization feed and downconverter that we tested at MUD 2019.
My first true-DSN X-band reception happened in May 2020. I was able to receive and track Bepi-Colombo, which at that time was 15.2 million km away from Earth. The signal was received with the feed built by KC2TDS mounted on a 1.2m f/d=0.6 offset dish steered by a Yaesu G-5500 az/el rotator. I used a Kuhne LNA-8000B low-noise amplifier connected directly to the probe, and the amplified signal was sent to the N2QG downconverter (LO=8GHz) mounted on the boom. Downconverted signals (400 – 450 MHz) were received using an AOR AR-5000. The radio’s IF was sampled by an SDR-14 and displayed with SpectraVue. Tracking of the probe was with PstRotator’s DSN feature.
Figure 1 – Block diagram of N2QG’s X-band Amateur DSN station in June 2020.
I purchased a squeezed-tube depolarizer and super Kumar scalar ring from M0EYT (from uhf-satcom.com). KC2TDS terminated it with a waterjet-cut copper disk and added a probe which he carefully tuned with the VNA to get <20dB return loss in the 8.4 to 8.45GHz DSN band. I mounted this feed on my 3.5m dish and was able to receive Mars Express, MRO, and OSIRIS-ReX.
Despite carefully tweaking the feed, I’ve been unable to get the system mounted on the 3.5m dish to yield the signal levels that I’m expecting. I suspect surface accuracy is the culprit because the 3.5m dish behaves well at 1296 MHz, but the g/t is just not there at 8.45 GHz. I can receive Bepi-Colombo on the 1.2m dish with around 12 dB compared to 16dB on the 3.5m dish. However, M0EYT receives it at around 30dB on his 2.4m prime dish. In July I worked on decreasing the SNR of the downconverter, which improved signals some, but definitely not as much as I would have liked to receive from a 3.5m dish.
Towards the end of that month I returned the X-band feed and downconverter to the 1.2m offset dish because I needed the 3.5m dish to participate in the EME SSTV Moon Landing Party hosted by PI9CAM at Dwingeloo Radio-Observatory in the Netherlands.
Juno remains out of my reach, so I’m considering next steps to improve my system. I thought that this would be a good point in time to summarize my experience so far, and discuss out loud plans for the future in case that it helps someone else who is just getting started in Amateur DSN. CLICK HERE for my whitepaper “Amateur DSN Lessons Learned (so far…).”