[amsat-bb] Re: J-Pole Antenna

[Werner, HB9BNK]

Thank you for your advice - very much appreciated.

The beauty of the J-Pole, I have in mind, is, that it contains 
both 2m and 70cm Systems on one mast - so I could simply attach 
the two cables going to the IC910 directly .... hi

The little yagi, I used, has a gain of 5.5 dBd for 2 meters and 8 
dBd for 70 cm. So, I guess, you say, investing time for the 
defunct rotor is better spent than trying omni.

Yes, I must find a solution for this.




Am 13.05.2013 19:12, schrieb Robert Bruninga:
>> The antenna, that I want to build, is described in a paper (probably 20
> years old)
>> by Dick, WD4FAB, titled 'Antennas for microsat ground stations', and the
> paper
>> describes the large time, a LEO remains at low elevations - about 76 %
> below 20 degrees -
>> and then concludes, that this is fine for a J-Pole.
>
> Absolutely true with respect to the*antenna pattern* but the current batch
> of LEO satelltes even though they are in the main beam of the omni antenna
> at the horizon, are -too-far-away- to be heard with only 2.1 dB of omni
> dipole antenna gain.
>
> So yes, those are good "satellite antennas" for omni coverage, but they
> wont hear anything that low because the satellites are 3000km away and the
> current crop of satliltes mostly operate in the 1/2 watt or less area.
> The only thing you will hear down to the horizon with these antetnnas is
> the ISS that is operating at 10 watts or more.
>
> You are better off simply giving up on the horizon (for an omni) and
> increasing your gain higher up.  And a 1/4 wave whip over a ground screen
> will give you 5.1 dBi instead of 2.1 dBi.  And then you may begin to hear
> things above about 15 degrees or so (and 3 dB better than you would hear
> on any antenna optimized for the horizon..
>
> And it is even better  to go to a 3/4 wave vertical over a ground screen
> and then you get almost 7 dBi gain starting around 30 degrees.  You wont
> hear the low satellites (you can't anyway on an omni) but you will hear
> them much better when they do get above about 25 degrees... (but notice,
> this is less than 1/4th of all passes).
>