[amsat-bb] Re: L Band Uplink Ant

[Edward R. Cole]

At 12:21 PM 9/27/2006 -0500, Wayne Estes wrote:
>
>Les W4SCO
>
>What do most folks use for a L Band uplink antenna?
>
>Wayne W9AE replies:
>
>The Teksharp 4-foot mesh dish kit was popular in the final months of 
>AO-40 operation.  Most people used it with a dual band patch feed, so 
>one dish is used for L-band uplink AND S-band downlink.  The TranSystem 
>AIDC downconverter from K5GNA worked well in this setup because it 
>doesn't require extra filtering to reject strong L-band TX signals.  The 
>4-foot mesh dish has less wind load than a solid 3-foot dish and more 
>gain than the biggest yagi or loop antenna.
>
>Wayne Estes W9AE
>Oakland, Oregon, USA, CN83ik

Wayne,

While theoretically a 4-foot dish at 1268 MHz should exhibit 22.6 dBi gain,
the dish is small in wavelength at this frequency.  The minimum size a dish
performs well is > 10 wavelength (a 4-foot dish is 1.2m in diameter which
is about 5 wavelengths at 1268).  The result is higher sidelobes in the
pattern and lower efficiency since too much radiation is in the sidelobes.
In fact it probably does not reach the theoretical gain level.  A single
45-element loop-yagi is probably equal to a 4-foot dish on 1268 MHz.

That being said, there is the benefit of using it as a dual-band antenna on
1268/2401.

For Eagle on mode S/C the mesh may not be fine enough (openings need to be
< 1/10th wavelength at 5800 MHz).  If it has fine enough mesh than it would
be a good candidate for Eagle later on. 
73's,
Ed - KL7UW 
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