Cutting-edge diy projects
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.
This weekend’s detection: STEREO-A received on X-band using 1.2m offset dish:
I received a squeezed-tube depolarizer and super Kumar scalar ring from Paul M0EYT (from uhf-satcom.com). Jason 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.
My plans for this weekend are to take down the 23cm EME feed from the 3.5m dish and test this feed after taking some measurements with the horn that Jason KC2TDS built based on Michal SQ5KTM’s design.
IMPORTANT UPDATE 1 June 2020: Please see https://www.prutchi.com/2020/06/01/probe-location-for-squeezed-tube-x-band-dsn-feed/ for the correct probe orientation!
I finally got around to building a 3.5-turn helical feed for the 1.2m offset dish to receive S-Band satellite and DSN signals. VSWR is quite OK (1.5:1 to 1.6:1) within the Near-Earth and Deep-Space S-band (2.2 to 2.3 GHz):
This feed works much better than the PCB LPA with which I started my experiments. Here is USA159 (DSP-21):
Click here for high-resolution version of the image.
DSP-F21 is a satellite of the US Air Force’s Defense Support Program (DSP) which operates the Satellite Early Warning System. The TLEs for this satellite (USA-159) are distributed by SpaceTrack. The satellite was launched in 2001 and is still used for missile launch detection. The satellite emits a constant carrier at 2237.5 MHz which sometimes becomes active with data during Early Warning and LEO SIGINT operations.