This is the completed dish feed. A commercial "chaparral" or scalar feedhorn was on hand but the rear part of it had a large waveguide flange. I wanted to use a circular horn feed of the VE4MA type since this was eminently suitable for the dish's 0.4 f/D. So I made a "soup can feed" and arranged a simple clamp of copper strip to fix it to the waveguide flange. The waveguide port on the diecast chaparral horn was filed to make it into more of an elliptical cross section, in an attempt to provide an "easier" transition to the circular soup can section.

The soup can measures 65mm inside diameter and is 110mm long. A probe, 24mm long, extends into the can and is some 38mm from the backplate of the horn(can). The probe is fitted to an sma socket which was soldered to the outer surface of the can. A suitable length of 3mm o.d. brass tubing was soldered over the centre conductor of the socket to make the probe. Directly opposite the end of the probe, I fitted a similar length brass screw, set in a brass nut soldered to the outer surface of the can, the idea being to give a small amount of adjustment to the cavity. In practice, however, the screw adjustment was found to be unnecessary, as it made no difference to the performance of the feed. The soup can arrangement, together with the existing circular feed section of the chaparral horn, forms a sufficient length to make a reasonably efficient dish feed. No definitive gain measurements have yet been made but the performance in actual use is very encouraging. The horn is fed with a 1.8m length of Andrew FSJ1-50 heliax that was already professionally fitted with an sma connector at one end and an N connector at the other. The sma connector fastens straight onto the transverter while the N type connects to a short length of semi-rigid line which in turn connects to the feed horn via an sma plug. This arrangement, with the heliax included,results in approximately 0.65dB loss ... quite acceptable for terrestrial use!