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Author Topic: NVIS Antenna For Satellites??  (Read 281 times)

KD0GS

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NVIS Antenna For Satellites??
« on: June 07, 2021, 02:26:49 PM »

Ok, a screwball idea I've been toying with. I've got a Workman UVS300 high gain dual band antenna I'm not using at the moment. What if I mounted it close to the ground, with it laying down, horizontal. About 1/10 of a wavelength above the ground for 2 meters. I've got some Andrews 1/2" Heliax I could run out to it to keep feedline losses low. Maybe put a chicken wire reflector screen under it? Would this work as a VHF/UHF NVIS antenna for satellite passes? I think I'm going to try it anyway, won't take much to jerryrig it up. LOL
I've done quite a bit of searching for VHF NIVS antennas and so far I've found nothing.
73, Jerry, KD0GS
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W9IQ

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Re: NVIS Antenna For Satellites??
« Reply #1 on: June 07, 2021, 02:33:28 PM »

Nothing wrong with experimenting but you generally don't want NVIS characteristics for an amateur radio satellite antenna. You need maximum gain when the satellite is at your horizons and much less gain when the satellite is at its maximum elevation from your location (local perigee).

The relative antenna gain needed is determined by the satellite's distance from you (ignoring close to the horizon effects). You can calculate it as 20Log(d). You can get a feel for the distances during a pass by using one of the satellite tracking apps.

- Glenn W9IQ
« Last Edit: June 07, 2021, 02:53:05 PM by W9IQ »
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- Glenn W9IQ

God runs electromagnetics on Monday, Wednesday and Friday by the wave theory and the devil runs it on Tuesday, Thursday and Saturday by the Quantum theory.

N4UFO

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Re: NVIS Antenna For Satellites??
« Reply #2 on: June 07, 2021, 03:59:43 PM »

Besides... the time spent 'directly overhead' is far less than most people think. If you were to watch a LEO satellite go over, it would be more like the proverbial train passing by with the horn blowing. It comes at you, does seem to be moving all that much relative to you, then woosh it flies overhead and slows down again on the other side. AND the doppler of the tuning will change rapidly during the 'overhead' just like the horn/whistle of a train drops a lot in frequency as it passes by.

I'd say you'd be much better off with a squalo/loop or some other omni antenna up higher than you would a ground plane on the ground. Mind you ALL of these are compromise antenna compared to a pointed yagi. When I first got started at home, I built a couple WA5VJB Cheap yagis, aimed them around 20 degrees and mounted them on a TV rotator. Worked quite well for what it was. I lost the birds when they flew directly overhead, BUT that is not on all passes and goes fairly quickly. Usually by the time I got my rotator turned around the other direction it was beginning to descend in the sky. What would have really made it better was a proper uhf preamp as coax loss is not your friend on the weaker V/U sats.

But keep thinking... that's the fun of ham radio. Now the question is do you want to learn things doing your own experiments, or gather knowledge from other peoples mistakes/failures. The latter is cheaper...  ;D


If you want some antenna plans go here: https://www.amsat.org/station-and-operating-hints/

Go about two-thirds way down the page and start with WA5VJB's antenna for the handheld satellite version. The you'll see CJU, IOio, Lindenblads, etc.

For WA5VJB full yagi info go here: https://www.wa5vjb.com/yagi-pdf/cheapyagi.pdf

Myself, I made a 7 element cheap yagi 435 AMSAT and the two meter part of the IOio (aka a 2m CJU)

73, Kevin N4UFO
 
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WA6BJH

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Re: NVIS Antenna For Satellites??
« Reply #3 on: June 07, 2021, 06:24:28 PM »

I’m surprised you couldn’t find something.  In the early days of satellites, crossed dipoles fed out of phase placed a few feet above a metal screen of some type was an effective low-earth orbiting satellite antenna.  The polarization was horizontal and omnidirectional at low radiation angles and the polarization was circular at higher radiation angles.  It’s been in the ARRL Handbook or Antenna Book for years.  Cheap and easy.  I had one and it worked great. 
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N4UFO

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Re: NVIS Antenna For Satellites??
« Reply #4 on: June 07, 2021, 08:04:46 PM »

I’m surprised you couldn’t find something.

Not sure if you are talking to me or the OP. HE is asking about using a vertical on the ground... we both advised him probably not. What isn't that couldn't be found? If you are talking to me, I wasn't looking for such an antenna, I was looking to put up a yagi. I was pretty successful with it as I worked into both EU and Africa with it on trans-Atlantic passes. I don't think the crossed dipoles would have done that, but that's just speculation on my part.

For me, the early days of satellites was RS-12/13... a whole different ball game with that bird. It was primarily 15m up and 10m down, so my HF vertical in the yard worked. Not so much with today's birds.

73
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K4QE

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Re: NVIS Antenna For Satellites??
« Reply #5 on: June 07, 2021, 08:07:35 PM »

Jerry,

The term NVIS does not really apply to satellite communication since the intention is not to reflect the signal back to Earth.  That's why you won't find any articles for satellite communication utilizing NVIS.

NVIS (Near Vertical Incidence Skywave) is defined as propagation utilizing the ionosphere to enhance regional and local communication paths by the use of high angle radiation patterns.  It is useful on frequencies between roughly 1 and 10 MHz.

Satellite communication requires your signal to penetrate the ionosphere regardless of the angle.  As Glenn noted, the highest gain for satellite operation should be at the horizon, and a dome shaped pattern is ideal unless you are using a directional antenna with tracking capability.  Height helps to increase the radio horizon so you "see" the satellite sooner and longer.  This is in contrast to NVIS where lower heights are generally prescribed until ground losses start to become an overwhelming issue.

73, Tony
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