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Re: Mir, SO-35, RS-18 stuff.]



KD9KC writes:
>Don't think so.  If I can barely get my callsign in with 30 watts
>on a J-pole for the other stations covering over me then I either
>need a beam or more power.  This isn't rocket science.  There are

KF4FDJ writes:
> The JPole exhibits gain by focusing radiation at the horizon (at the
>  expense of overhead).  So, this antenna will only deliver the calculated
>  ERP at low elevation passes.  Also, since it is linearly polarized, it
>  will be subject to an approximate 3 db (half power) fade as the
>  satellite rotates.  During overhead passes the signal will pass in and
>  out of various lobes and nulls, further contributing to signal fading. 
>  If I required a fixed antenna for LEO use, I'd build (or buy) a QHA,
>  turnstile, eggbeater or Lindenblad antenna.

Some comments on the "J-pole as a satellite antenna" discussion....

The J-pole does not have any magical properties, despite the claims often
associated with its use.  The radiation pattern is not much different from a
monopole or ground plane antenna, except it is asymmetrical.  In the
direction from the main mast through the matching stub, it has about 2.5 dB
gain over a GP--about 4.3 dBi free space gain.  In the other direction,
however, it is about -1 dB compared to the same GP at the horizon and very
similar from 15 degrees and up.  The terrestrial "gain" often observed from
it's use may be simply from the higher radiating point (it is twice as tall
as a 1/4 wl GP).

Considering it's large relative size and it's often-difficult matching
system, I would not recommend it as a home-brew project.  Instead, a
high-performance ground plane antenna is much easier to build, eminently
simple to tune, and will provide a perfect omnidirectional pattern.  Neither
of these antennae are very desirable as satellite base-station antenna due
to their low overall gain and linear polarization.  Mike's recommendations 
above
are sage advice.

73,
Jerry, K5OE
The farthest west ham in west Houston :-)
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