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Re: Multi-Band-Parabol-Feed...where to order ?



>From: "Jens Spiess" <jspiess@dplanet.ch>
>I like to change my single & 2-band-feeds in my parabol-dish systems.( 5 m
>dish;f/d 0.5 and 90cm dish;f/d 0.4)
>
>Anybody knowing where I could ORDER MULTI-BAND-FEEDS should be for
>LHCP/RHCP-switching
>(..and linear vertical/horizontal switching available too..) for
>70cm/23cm/13cm/6cm/3cm...but ALL-in-ONE FEED-UNIT
>together.(Log-Periodic-Feed....?)

Jen,

To cover all those bands and polarity combinations and at >100w...???

I doubt that there is any commercial dish feed available {I'm afraid this
one is "pie in the sky"}.  I am unaware of any ham designs, either!  That
is a tall order you have specified.  I suppose a crossed log periodic might
work, but designing/making/getting one that provides good dish illumination
at all those frequencies is pretty tough...maybe impossible.

Instead for the 5m dish, you might consider multiple feeds [separate one
for each band] that are mounted on a rotating turret so as it is rotated,
the desired feed is placed in the focal point.  Still quite an engineering
feat to accomplish.  I supose each feed would be a crossed dipole in front
of a reflector [or a circular horn with orthogonal coax probes].  You would
need a complex phasing/switching network for each feed.  For the 90cm dish,
I think the turret idea would block the dish aperature too much.  For small
dishes [unless they are offset fed] it is probably best to stick with
simple one-band feeds.

Another approach for the 5m would be using a cassegrain subreflector.  Then
all the feeds could be mounted behind the dish aiming thru a hole in the
dish center.  Since the sub reflector shades the center of the dish it will
suffer some loss of efficiency [gain].

Ed
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