Jason Meyers (KC2TDS) and I have been working on a circular polarization feed and downconverter to mount on the 12′ dish for X-band (8.4 – 8.45 GHz) amateur DSN reception (receiving signals from planetary probes using Deep Space Network frequencies).
The feedhorn is based on the dimensions of the one constructed by Michal SQ5KTM:
We used McMaster-Carr materials for our version of the feedhorn:
Jason KC2TDS carefully handcrafted the squeezed-tube depolarizer and built the feed:
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!
We measured the feed’s gain, circularity ratio, and beamwidth at Microwave Update 2019:
Results were as follows:
Gain – 13.2 dB with a linearly polarized signal normal to polarizer inserts
Circularity: -2.5 dB with horn rotated 90 degrees
-3 dB Beamwidth: 33 degrees
S11: -18.5 dB at 8.45 GHz
We plan to place a Kuhne Electronic KU LNA (model 8000 B, 8000 to 8450 MHz, 28 db Gain,
0.8 dB NF @ 18 °C) right at the feed.
Measurements taken at Microwave Update 2019 showed a 0.9 dB NF and 29.5 dB gain at 8.45 GHz for our unit.
The LNA will feed the 400 – 450 MHz IF downconverter that we built:
We also tested the downconverter at Microwave Update 2019 and found that it has a measured noise figure of 4.58 dB and a gain of 24.4 dB.
Next step is to mount the setup on the dish and start experimenting with real DSN signals.
We’ll provide more details and updates as we continue working on this project.