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Re: AO-40 Dish Size



At 06:59 PM 5/8/2003 -0700, Dave Smith - W6TE wrote:
>Hi guys,
>
>After many years of being absent from the birds, I'm going to give AO-40
>a whirl and need some advice regarding the 2.4 GHz. downlink dish size.
>I've listened to the BBQ debate and jabs for the last couple of months
>and I'm asking for some input as far as what would be a good compromise
>for dish size vs. pointing accuracy while establishing a decent noise
>floor. I have a DEM receive converter that will be located at the feed
>point and I'm looking at buying G3RUH's splash feed (or other
>suggestions?). I have a 3' commercial dish (Mark) that could be pressed
>into service as well as a 7.5' TVRO dish. I have available several
>rotors that could be used eg. Orion, HD-73, Ham IV, 5400 AZ/EL, and TVRO
>elevation positioner. I will probably stick with manual control rather
>than computer control if I used the TVRO positioner. 
>
>Your thoughts please.
>
>Thanks,
>
>Dave Smith / W6TE 

Hi Dave,

I read the rest of my e-mail thinking someone would respond.  Well here goes:

First you mention a 3-foot dish (commercial? Mark?).  I'm not sure what you
are saying it is, but if it is a circular solid metal or composite
construction it is completely adequate for AO-40 mode-S reception, using a
good feed and preamp/convertor combination (your DEM is fine).  If mode-US
is your intention then this is all you need have along with a UHF yagi.

I use a satellite TV dish that measures 33-inches (85cm) and is the
direct-TV style of offset feed (they are obtainable up here in Alaska from
Radio Shack, since this is the min-size for sat-TV reception...actually
used for TV until I upgraded to a 39-inch dish).  I use a B5400 az-el
rotator with a M2 436CP42 x-yagi for uplink and the dish for downlink with
no trouble (survived the >65 mph wind storm and three Alaska winters so
far..the 1.2 GHz loop-yagi and M2 were broken in those storms but not the
rotator).

If you have an idea of trying mode-LS, I would look at using the 7.5-foot
dish for both uplink (1269 MHz) and downlink (2401 MHz) using a dual-band
patch feed (others on this reflector can point you to information on
building or buying the patch).  Modifying the standard dish using the TVRO
positioner is possible (again refer you to others that have a website
showing how).  For azimuth drive of the 7.5-ffot dish it will take a HD
rotator and good thrust bearings to take the stress off the rotator (the
Orion should suffice).  The HD73 & B5500 type is too small for this in my
opinion...not sure about the Ham-IV.

I have an 8-foot commercial ku-band satellite earth-station az-el mounted
dish that I will be setting up for mode-LS.  It currently is tied in one
position as I have not got the az-el drive operational.  It will also be
used for EME later on.  But I know not everyone is fortunate to obtain such
an antenna.

Hope that helps your decision making.

73, Ed - AL7EB
 

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