[amsat-bb] DH 80cm dish and helix feedhorn

[Kc2hax@xxxxxxx]

Hi Jerry et al.,

Thanks for the kind comments. One of the best things of AO-40 is that it is an
excellent experimenting platform. It is giving us a lot of opportunities
for continuos hands-on learning, the only problem is lack of spare time (or
should I say that the spare time is the one we use in our other live
ventures outside satellites) to address all that can be experimented.

The other great thing with AO-40 is S band: 2.4 GHz is the ideal microwave
entry level frequency, wavelength is small enough to really enjoy quick
antenna experiments and big enough so accuracy is not a killer. Very well
balanced indeed. And yeah... I have a large inventory of mode S spare
antennas in the garage here in W2 and also in my EA  QTH from the AO-13 days
(Yes, I even did mode S patches also -with no succes at all- in the AO-13
days)
Re your proposal on additional testing requiered (btw, I was somewhat
expecting this ;-)), It is going to be a bit difficult to make a fair
comparison because it is not easy to mechanically setup the UEK on the
Connifer focus in a way that could be properly compared with the TSI (the UEK
has a very bad form factor to be in the focus of any dish). Testing the TSI
with the 80cm dish and helix-cup feed is easy -this will be my  next try-
altough I will not have the side by side subjective comparison...
In any case, next weekend time permitting (we are in the middle of the
soccer and fall baseball season ;-)) will try it. Stay tuned.
BTW, I received some requests for more detailed pictures and prepared a 
page with more graphic details here
http://www.qsl.net/kc2hax/ant/feedhorn.htm

Best 73 de antonio, kc2hax/ea4le

 
  
 

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Tony, 
Great pictures... and so much work! Thanks for sharing them. I am sure they 
will give many people the incentive to build up something. I see from some 
of your other pictures you have built lots of now-spare systems--I have a 
garage full of those also :-) The helix with ring-reflector is very nice 
looking--those are especially nice for a compact portable system. Mine 
worked just fine for UO-11, but as we all now know, UO-11 is much easier to 
hear than S2 SSB on AO-40. 

You indicated the performance of the two systems was comparable. The BIG 
question everyone will sit on the edge of their seat to hear is... (drum 
roll, please): can you swap either the UEK or the TSI d/c from one antenna 
to the other? With that comparison you will get a narrower comparison of the

dish+feed options. I never had a 3733+dipole feed up to compare to the 
helix+cup feed. 

A neat idea would be to take the stock TSI system supplied by K5GNA (dish + 
3733), remove the dipole feed, and add an extension of some type to fit a 
helix+cup right at the calculated focus. The feed line would run up the 
center of the helix--coaxially. With a wire mesh screen on the dish, a 
plug-and-play feed replacement like this would be a popular item, I am sure,

to gain 2.5 - 3 dB. 
73, 
Jerry, K5OE 
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