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Re: 23/13cm dual helix feeds - response


              Frederick I`d like to thank you for your attention about 
dualband Helix feed 23cm/13cm dish. I`m going to use 2.4m parabolic dish 
antena, but I have not sure what kind of feed will be the best for it. I 
was found some example of monoband feed with single halfwavelenght active 
element instaled in one side open tube box area (or somethink like it). It 
work only in horizontal or vertical polarization. I didn`t find anything 
for dualband work (23cm/13cm). I found only one conception of dualband feed 
 for 6cm/3cm band.
              I`d like to use my 2.4m dish for AO40 fullduplex work (up 
23cm/dwn 13cm) and for EME test also.  What kind of feed will be the better 
for 23cm/13cm EME work (maximum gain dB)? Is the possibly to build good 
(without less dB) dualband feed dor 2,4m dish(with saved good area function 
on each band)?
              I think then 3dB to 6dB drop in level when use Helix feed its 
to much for EME dish antena. I will try to use 2.4m dish for it, and 6dB 
down level is like normal 1.2m  dish.  The 2.4m dish with good make feed 
will give 27 to 28 dB on 23cm and nearly 33dB on 13cm band (I think so)??
              If you have some experience in "normal" dualband feed please 
give some info about.

Best regards

Rafal SP9VFD

Od:	Frederick M. Spinner [SMTP:fspinner@hotmail.com]
Wys?ano:	30 paYdziernika 2001 22:08
Do:	amsat-bb@AMSAT.Org
Temat:	Re: [amsat-bb] 23/13cm dual helix feeds - response

>From: "Gunther Meisse" <gjmouse@neo.rr.com>

>I have just completed building a dual 23/13cm Helix feed for a 60cm >dish. 
>I will use same as a portable rig. So far I have tested the >13cm downlink 
>portion with very good results. I am comparing it with >my 1.2m dish. As
>expected I see about 3db drop in levels.

This is rather amazing in and of itself, because gain in a dish antenna is 
function of area and not diameter...

This means going from a 120cm dish to a 60cm dish you should have seen
levels go down 6 dB.  It's true, I'm not making this stuff up...

3 dB would be more like going from a 4 footer (120cm) to a 3 footer

Fred W0FMS

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