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.
I am aware of the fact, that the microsats (AO-16 et.al.) had a mean altitude of 800 km, while my 'targets' fly (sometimes) at higher altitudes. So, some problems are to be expected.
(In fact, I was working with a small yagi with fixed elevation of about 15° for several years but my rotor has problems and the access to it is complicated and the repair also, so that I decided to try something simpler until the rotor is fixed - or replaced. Living in a tight environment, I cannot put up a nice antenna system, but to compromise is part of our hobby.)
So, I keep you informed about my results.
73 Werner, HB9BNK
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).
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).
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.
73 Matt W5LL
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 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).
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participants (3)
-
Matt Patterson -
Robert Bruninga -
Werner, HB9BNK