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Re: dish

On Saturday 15 June 2002 15:01, Al Zoller wrote:
> Hello all,
> I've just been fortunate (I think) enough to have been given a dish.
> It is a Channelmaster designed for Ku band (11.7 to 12.2 GHz).
> Offset feed, 90 cm wide, 98 cm high, 8.5 cm deep in the center.
> The feed is a circular horn and I have no idea where it's focus is
> but it is 70 cm from the center of the dish to the back of the
> flange that the horn mounts on.

This sounds like the slightly smaller version of the 1.2 meter 
Channelmaster dish made for Primestar.  I believe that Primestar
used three different versions, one small oval dish and the 1  and 
1.2 meter dishes.

> Does any one have any experience with  a dish like this?

I'm using the 1.2 meter model and it works great on AO-40.  Building a
simple 5-6 turn helix feed is easy and can be accomplished in an evening.
Mine consists of six turns of number six copper wire, wound on an inch and
a half diameter plastic pipe.   I used a platter from an old hard drive for
the reflector,  mounted a chassis mount 'N' connector on it and  soldered
one end of the helix to the connector, then placed a small plastic clamp half
a turn away to help support it.

Pictures are at:

I used a number of small mirrors attached to the dish to determine the
true focal point and it appears to be a couple of inches in front of the
mount.  The typical 5-6 inch reflector on a helix does get in the way and
on mine I've not taken the time yet to get the helix positioned exactly
right, but I'm having no trouble working the satellite, even with the feed
a little too close to the dish.

On my old FT-726R with a transystem downconverter with only the crystal
modification I get a background noise level of around S-3 with the beacon
coming in at a solid S-9.

Hope this helps.

Ken,  N7IPB

> Any help/advice on converting to 2401 MHz would be appreciated.
> Thanks,
> Al,  N7UB
> AMSAT LM1505

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