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followup on feed blockage



In earlier correspondance, I made the comment to Tony, AA2TX, that I 
believed the blockage loss for a 4" diameter feed in a 24" dish to be on 
the order of 0.08-0.10dB.
I have since found my calculations to be in ERROR...direct integration of 
the aperture field, and cross-checking with another published result, I now 
believe the answer to be about 0.45dB due to blockage.  I still believe 
(and the cross-checking confirmed) that the assumption of an infinite edge 
taper overestimates blockage loss, but then again 0.3dB isn't much to argue 
about :-)
I have generated a couple of useful graphs for blockage, showing both gain 
loss and sidelobe level increases, and hope to have it up on my website 
later this week.
Sorry for the miss,


Scott Townley NX7U
Gilbert, AZ  DM43di
http://members.cox.net/nx7u

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