Feeds with squeezed-tube depolarizers are popular among amateur DSN enthusiasts because of their straightforward, no-tune construction. Luis Cupido CT1DMK published a design that is often followed, and has been used successfully by Paul Marsh M0EYT, Micha? Zawada SQ5KTM and other hams interested in DSN.
Signals from planetary probes are weak, so as many variables as possible need to be eliminated when first setting up and debugging an X-band system. One of them is the polarization of the antenna. I found myself in that situation, and after some experimentation plus helpful answers from hams on the Amateur-DSN groups.io board, I’m now certain that I have the probe correctly oriented for DSN DXing.
As shown in the figure, an LHCP feed is needed to receive the RHCP signals transmitted by the vast majority of DSN spacecraft (when operating nominally). This is because when the feed is mounted on a parabolic antenna, the feed’s LHCP signal becomes RHCP after being reflected by the dish. The exception to this is for Cassegrain or Gregorian dishes, where a a secondary reflector is used to direct the energy into the parabolic reflector from a feed antenna located away from the primary focal point. In this case, the RHCP signal becomes LHCP at the secondary reflector, and then back to RHCP again when reflected by the dish.