[amsat-bb] Re: J-Pole Antenna

[Robert Bruninga]

> As has been said many times, most satellite passes are never
> "directly overhead", but rather on some inclination across the sky.
> A 5 element yagi antenna, at a 35 degree angle from the horizon,
>  with only an asmuth rotator, will let you work far more satellites for
the money spent.

Except that the correct angle is 15 degrees not 30 or 35.    At 15
degrees, the main gain lobe of the antenna still has excellent gain on the
horizon where you need it most and an equal gain all the way up to 30
degrees or so.   Below 30 degrees is where satellites spend 80+% of their
in-view times.  This is where you need the gain most.  But when the
satellite is above 30 degrees, the satellite is at least 6 to 10 dB closer
and so it makes no sense to sacrifice gain on the horizon (where you need
it most) by placing it at 30 degrees where you need it least.

See http://aprs.org/rotator1.html

Ignore the topic of the page but look very carefullyl at the SCALE drawing
(Yes, that is drawn to scale) of a LEO satellite pass  Notice how 95% of
all satellite access times are below 50 degrees and 70% of the time they
are below 22 degrees.  That is where you need the gain.  Do not waste it
by tilting the antenna up more than 15 degrees.

The only exception is that if your beam antenna cannot see the horizon
anyway, then, yes, tilt it up a little more since you wont hear the low
stuff anyway...

Bob, WB4aPR



Gregg Wonderly

On 5/12/2013 12:48 PM, Jeff Moore wrote:
> I wouldn't recommend a J-pole for satellite work unless you expect to
> only work sats on the horizon.  The J-Pole antenna has a low take-off
> angle and almost NO radiation overhead,  an plain 1/4 wave ground
> plane antenna would work better for the sats.
>
>
>
> J-poles are great terrestrial communications antennas, not so much for
> working overhead satellite passes.  An Eggbeater or quadrifiliar
> antenna would be a better choice.
>
> 7 3
>
> Jeff Moore  --  KE7ACY
>
> On 5/12/2013 8:00 AM, Werner, HB9BNK wrote
>> Thank you all for your valuable hints and advices !
>>
>> I will now build such an antenna and then supply here the results.
>>
>> 73 Werner, HB9BNK
>
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