[Moon] offset superiority on 3cm eme

[Edward R Cole]

Dom,

I picked up on that.  My thought is that if one is using a very small 
dish on mw eme, an offset feed dish would be preferred as it nearly 
eliminates feed blockage and signal scattering by feed and 
supports.  Also seems there are more offset feed dishes available in 
the smaller sizes.  Center-feed design are available as surplus in 
larger sizes.

Of course if you are making your dish vs buying something, offset 
feed is more difficult to make.

Up here (in Alaska) we have a history of Ku-band satellite dishes 
starting with 1.8m (6-foot) in the late 1980's.  There are quite a 
few 1.2m (4-foot) offset dishes still in use up here (I have one 
still in use for my sat-TV).  New satellite dish installation's are 
typically 76cm to 85cm now that several satellites have redirected 
footprints to favor northern latitudes.

I have one 45cm dish that I re-purposed for ham radio with a W1GHZ 
dual-band feed with corrugated conical feed horn for terrestrial 
operation.  I have two more 45cm dishes on the shelf (18-inch 
standard for satellite).  I also have an 85cm  offset dish I 
installed a 2.4 GHz helix feed for ham satellite use (mode-S) several 
years ago.  That dish came from my TV system when I upgraded to a 1m 
dish.  I have two 1.8m center-feed commercial 6-GHz dishes FREE for 
pickup in AK (they will fit in the bed of a pickup truck).

So in the US/CA probably there is a good selection of smaller offset 
feed dishes obtainable from the satellite-TV industry (used and 
new).  Dual-mode feeds or narrow beamwidth horns will be needed to use them.

73, Ed - KL7UW

At 10:13 AM 10/26/2014, Dom DEHAYS wrote:
>oooops forgot to tell the 1m and 1m20 are offsets
>
>73
>Dom
>----- Original Message -----
>From: <mailto:f6dro at wanadoo.fr>Dom DEHAYS
>To: <mailto:moon at moonbounce.info>moon at moonbounce.info
>Sent: Sunday, October 26, 2014 6:05 PM
>Subject: [Moon] offset superiority on 3cm eme
>
>Hello ,
>
>I've MEASURED here on a 1m dish , 0,6/0,7dB NF waveguide system 
>9,7dB of sun noise and 0.2dB of moon noise (SFI 110)
>On a 120cm offset , same system , I get 10,6dB* sun noise and 0,3dB 
>moon noise. With the 120cm , the system is a bit below optimal , 
>normaly 11dB of sun noise should be possible.
>With the 1m system , I've worked 4 different stations  IN CW and 
>heard some more.
>
>73
>Dom
>
>
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73, Ed - KL7UW
http://www.kl7uw.com
     "Kits made by KL7UW"
Dubus Mag business:
     dubususa at gmail.com
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