[Moon-net] "Super VE4MA" test results on 23cm

[peter blair]

I am reporting here on some tests on a Super VE4MA feed constructed for 23cm. My dish is 6m diameter with a 0.375 f/d . The feed used for many years was very close to the original VE4MA with a 0.71L circular guide and a 5 screw polariser. The original choke (cavity) is 0.5L wide and 0.45L deep with the choke set back by about 0.05L. Its position had been optimised previously and the physical focus was very slightly in front of the guide aperture.
The method used to construct and secure the choke made it possible to change it fairly easily and quickly and so a second choke was made to the dimensions of the "super VE4MA " described in the Wurtzburg eme conference proceedings. This has a width of 0.6L , a depth of 0.45L, and the choke set back by 0.15L.
 Sun noise today, 1430 z with the original choke measured 17.2dB with a SF of 80. This is measured with an IF attenuator ahead of a 360KHz wide receiver.
Replacing the choke with the " super " version  gave the same figure 17.2dB 
However, moving the feed forward so that the physical focus was 0.15L inside the aperture (the phase centre defined  in the W1GHZ paper) gave 17.7dB, a gain of 0.5dB. (This is in fact  the level of improvement indicated by the paper for the super VE4MA compared to the original.)
There may be a small further increase when I fully optimise the aiming angle of the feed so that is absolutely co-axial with the focus, I was beginning to run out of time. 
First and second peak sidelobes were briefly explored in vertical and horizontal planes and seemed to be at the -26dB level with well defined nulls. This is a better result than I would (intuitively) have expected.
I would be interested to hear of any other results.
73 Peter G3LTF