[amsat-bb] Re: Commercial Mode L Antenna sources

Wayne Estes w9ae at charter.net
Wed Jul 2 10:33:49 PDT 2008

I'm surprised how few people have mentioned parabolic dishes during this 
discussion about commercial Mode L antennas.  L-band uplinks are mostly 
used in combination with a S-band downlink.  Most people build L/S 
equipment with HEO satellites in mind.  A single yagi or helix doesn't 
usually provide sufficient gain for L/S band use with a HEO satellite. 
You need the gain of a dish for satisfactory S-band reception of a HEO 
satellite.  So one practical solution is an oversized dish with a L/S 
dual-band feed (helix or patch).  A 4-foot dish was proven to work well 
for this on AO40.  In my opinion a single 4-foot dish is more practical 
than, for example, cobbling together multiple yagi/helix antennas for 
S-band downlink and multiple yagi/helix antennas for L-band uplink.

My 4-foot dish and dual-band patch feed were purchased commercially from 
Teksharp (Rick Fletcher KG6IAL).
The dual-band patch feed is sold fully assembled and tested, but the 
dish was a kit.  I had to locally purchase 1/4 inch hardware cloth, cut 
it into 8 "petals", and use 200 zip ties to attach the petals to the 
frame of the dish.  A mesh dish has somewhat less wind loading than a 
solid dish.  That's important because a solid 4-foot dish has a maximum 
wind load of more than 12 square feet, exceeding the wind load rating of 
my G-5500 rotor.  A picture of my satellite antennas can be seen here:

Wayne Estes W9AE
Oakland, Oregon, USA, CN83ik

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