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




>A fellow reported using a JPole with 50 watt, and failing.  Using the 
>same calculations, here is his situation:
>        50 watts pep
>        1.75 db line and insertion loss (assumed)
>        5.5 dbi antenna gain (again assumed)
>        20.7 dbW EIRP
>        for an approximate ERP of 118 watts
>

A jpole is a really crummy antenna for transmitting to a satellite.
Here are some better numbers for the jPole at 15 degrees elevation
with bottom of the antenna at 25':

        +47dBm0 = 50W PEP tx power
        -1.75db = feed line loss
        0dB     = antenna gain at 15 degrees
        -6dB    = average polarization mismatch loss (not median)
        EIRP = +40 dBm0 or about 10 watts on average
        
>Commonly, portable users will use an ARROW (or similar) antenna and a 5
>watt HT:
>        5 watt pep
>        1.75 db line and insertion loss (assumed)
>        8 dbi antenna gain (assumed)
>        13.2 dbW EIRP
>        for an approximate ERP of 21 watts

Notice that the 5 watt HT with a manually pointed ARROW is 3 dB better
and doesn't have the deep fading problem.

>If I required a fixed antenna for LEO use, I'd build (or buy) a QHA,
>turnstile, eggbeater or Lindenblad antenna.

A Lindenblad is an excellent fixed station antenna. Here is the same station
with a Lindenblad at 15 degrees

        +47 dBm0 = 50W PEP
        -1.75 dB = feed line loss
        3dB   = antenna gain at 15 degrees
        -3 dB    = average polarization mismatch loss
        EIRP = +45 dBm0 or about 33 watts

The Lindenblad also does not have the deep fading problem but doesn't
require manual pointing.

Tony

        

Tony AA2TX@amsat.org
North Andover, MA

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