[amsat-bb] Re: J-Pole Antenna
mattpatt at 1starnet.com
Mon May 13 11:57:41 PDT 2013
Back when I was on the FM sats I used a small yagi for 2m and another
one for 70cm. I built a mast out of some 2" PVC that came out to a T
and had 45 degree elbows on it. I then mounted the antennas on the
elbows so that they were pointed roughly 45 degree up. The whole thing
was mounted to a cheap radio shack rotator. The rotator was mounted to
a metal fence post (t-post). The antennas were maybe 7' off the ground
at the highest point. I could work just about all passes with this
setup. Using one radio for RX and another radio for TX. Only passes I
couldn't work were either real low or I would loose signal for a few
minutes when I had overhead pass. Do a google on my callsign and you'll
find several recordings I made of suitesat with this setup that I have
uploaded to Soundcloud.
On 5/13/2013 1:02 PM, Werner, HB9BNK wrote:
> 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
>>> 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
>> of LEO satelltes even though they are in the main beam of the omni
>> 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
>> will give you 5.1 dBi instead of 2.1 dBi. And then you may begin to
>> 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).
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