[amsat-bb] Re: J-Pole Antenna

[Gregg Wonderly]

Bob, depending on the antenna pattern and the ground, as you say, 15 degrees 
might be too low for any additional help toward the horizon.  30 to 35 degrees 
will give you a little better results for stuff that isn't just right at the 
horizon, I feel.  As with all things in this hobby, experimentation with your 
equipment will allow you to find the best combination.

Gregg Wonderly
W5GGW

On 5/13/2013 11:29 AM, Robert Bruninga wrote:
>> 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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