Cutting-edge diy projects
1296 MHz was bustling with contest activity this morning. Great signals made it easy to tweak RX and tracking in preparation of next weekend’s EME SSTV Moon Landing Party hosted by PI9CAM at Dwingeloo Radio-Observatory in the Netherlands.
In preparation for tracking the UAE’s Hope Mars Mission, I also tweaked my DSN X-band downconverter to improve S/N. The latest configuration is as follows:
Click here for larger picture.
I’ve been planning ahead to the day when I retire, my girls live on their own, and my wife and I can finally take the big-RV roadtrip that we’ve been talking about forever. Not being one for sitting by a campfire, I’m always collecting equipment to take along, and some time ago my ongoing eBay® search for a collapsible parabolic antenna hit gold. It was for an EchoSphere 7.5 ft TVRO folding dish in mint condition. It even came with an extra (slightly damaged) reflector assembly to boot! My plan is to build feeds for 1296 MHz EME and S-Band DSN. Sadly, 10 GHz EME and X-band DSN are out of range for the reflector’s fabric.
The EchoStar RV-750 comes in a carry bag. It can be assembled and deployed in lessa than 10 minutes (c)2020 David Prutchi PhD N2QG
Finding information on this dish has been much more difficult than I had anticipated. I summarized my literature and experimental findings in a short write-up available at: The EchoStar RV-750 Antenna by N2QG Continue reading
I moved the X-band setup to the 1.2m offset dish to be able to characterize and diagnose. The problem is that I’m unable to get the system mounted on the 3.5m dish to yield the signal levels that I’m expecting. I’m suspecting surface accuracy 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 BepiColombo 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.
Is it time for my garden to grow a new large solid dish?
Today I tweaked the position of the feed and the VE4MA ring on the 3.5m dish. Signals improved quite a bit, with STEREO A at 9dB above noise, and BepiColombo at 15dB above noise. However, there is still quite a bit of room for improvement. I had to take down my measurement setup when the “severe thunderstorm” alert came in. Will try again tomorrow.
CLICK HERE for high-resolution image.
Lately I’ve been asked about the downconverter that I built to receive X-band DSN signals. Because of time limitations, I took some shortcuts, namely using commercial connectorized modules and a high-stability signal generator with integrated mixer (DS Instruments MX12000 Integrated-LO Mixer) instead of designing the circuit from scratch. The cost of the unit is thus relatively high, but it was either that or not being able to receive X-band spacecraft at all in the foreseeable future.
We tested the downconverter (without LNA) at MUD2019, and measured a 4.58 dB noise figure and a downconversion gain of 24.4 dB.
Yesterday I mounted the VE4MA with squeezed-tube depolarizer made by M0EYT (uhf-satcom) on the 3.5m dish using a bracket designed and fabricated by KC2TDS. The tube holder is 3D-printed nylon, while the bracket itself is aluminum cut with water jet.
It got late by the time I finished mounting the feed, so I didn’t have time to optimize the position of the feed and super Kumar ring relative to the focal point. Nevertheless, measured 11dB of Sun noise vs. cold sky.
This morning, before Mars would set, I was able to receive the Mars Express spacecraft. I could see on DSN Now that it was locked to Goldstone.
Fading in the signal shown below was because I still have to tweak PstRotor and the rotator controller (Green Heron) driving the BIG-RAS Az/El to deal with the very narrow beamwidth (0.69 degrees) produced by the 3.5m dish at X-band.
