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Old 02-04-2010, 09:56 PM
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CAV104 CAV104 is offline
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Default NVIS



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Anybody working NVIS? If so, how's it working out and how are you set up?
Old 02-05-2010, 02:32 AM
killdeer killdeer is offline
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Quote:
Originally Posted by CAV104 View Post
Anybody working NVIS? If so, how's it working out and how are you set up?
NVIS Near Vertical Incidental Skywave. Or to make matter short, Making your signal go straight up and come straight down so that you can talk to somebody close to you. I use this on 80 meters all the time as my Dipole is only 24 feet up at the center feed and comes down to within 9 feet.

Being this low on 80 meters allows me to talk to people ranging from 40 miles away to about 90 miles. After that it is not NVIS. and closer than that, it is just plain simplex.

We have a local rag chew at 1300 Mountain time on 80 meters and with the exception of one guy out of montana, we are all using NVIS.

What would occur without NVIS is that the signals would come down to far away and you would not be able to communicate with people that are close to you. 40 meters is a good example. during the day I often hear and talk to people 400 to 600 miles away from me. Yet, people that are 40 to 300 miles away I rarily if ever hear. Even when they are communicating with the same people that I am 500 miles away.

NVIS is also when you are talking about a High Angle of Take off from your radiated pattern. By running a Dipole close to the ground, you will get a high angle of take off because of the interaction of the Ground plane an your Radiation pattern. This High Angle of take off causes your radio wave to bounce off of the F layers and come back down to earth very close to your QTH. While a low angle of take off will cause your signal to come down hundreds of miles away.
Old 02-05-2010, 03:46 PM
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Good reads on NVIS.

http://www.w0ipl.net/ECom/NVIS/nvis.htm

You need Power Point for this next one

http://www.whenshtf.com/showthread.p...9-Thread/page3

http://www.tactical-link.com/field_deployed_nvis.htm
Old 02-06-2010, 09:31 AM
ohgary ohgary is offline
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Anybody working NVIS? If so, how's it working out and how are you set up?
NVIS is a technique for using an antenna and not an antenna itself.
NVIS is typcally used where you need no more than 200 miles range.
NVIS will work with most wire antennas, dipoles, offset feed, G5rv or long wires. Its works best on 80 and 40 meters. Usable on 30m but NVIS phenomenon doesn't work well on higher frequencies.

Its really interesting to see how well it works, We have a state wide special event and use NVIS for that. We have put up two antennas, one NVIS dipole about 10ft off the ground and another at 35ft. In state signal are 10-20db stronger on the lower NVIS antenna. Switch to the higher antennas and the stations outside the 200mile range are 10-20db stronger.
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Old 02-10-2010, 01:32 AM
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I use NVIS on 80 and 60. I use a single 4:1 current blaun feeding a crossed dipole with one leg being 80m and the other being 60m. The antenna is set as a inverted V with the apex being 15ft up and the ends being 3 ft off the ground. (it's modeled after a 2 band military HF antenna) Apparently it's circular polarized anddue to the polarization in theory it brings the signal down closer to your position than a NVIS longwire or single antenna allowing contact with stations from a few miles to a few hundred. (as long as they're set up in a similar manner) If using a low dipole for NVIS place a reflector 5% longer than the antenna under it to improve your performance.
Old 02-10-2010, 04:12 PM
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I use NVIS on 80 and 60. I use a single 4:1 current blaun feeding a crossed dipole with one leg being 80m and the other being 60m. The antenna is set as a inverted V with the apex being 15ft up and the ends being 3 ft off the ground. (it's modeled after a 2 band military HF antenna) Apparently it's circular polarized anddue to the polarization in theory it brings the signal down closer to your position than a NVIS longwire or single antenna allowing contact with stations from a few miles to a few hundred. (as long as they're set up in a similar manner) If using a low dipole for NVIS place a reflector 5% longer than the antenna under it to improve your performance.
How ya been kahn? I read something about using reflectors. I believe the operator used three. What do you think? More is better?

I'm in an HOA with restrictions. However, I did erect a 20' flagpole behind the house with 20 radials at 25' each. Works great.

I was thinking about hoisting a 40M dipole up the flagpole to somewhere between 10' and 15'. I could only do this after dark and it would have to be taken down when finished. I don't have the room to go 60 or 80M. Any thoughts?
Old 02-10-2010, 11:48 PM
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How ya been kahn? I read something about using reflectors. I believe the operator used three. What do you think? More is better?

I'm in an HOA with restrictions. However, I did erect a 20' flagpole behind the house with 20 radials at 25' each. Works great.

I was thinking about hoisting a 40M dipole up the flagpole to somewhere between 10' and 15'. I could only do this after dark and it would have to be taken down when finished. I don't have the room to go 60 or 80M. Any thoughts?
Using the flagpole, what if you erected a dual element inverted V in the shape of a swastika using magnet wire? Use the flagpole to hoist up the balun. It would still work and no one would be able to see it, you would just be limited to 100w. I imagine the radials / reflectors underneath it might help. Go 1/4 wave out then 1/4 wave over on each side of the 1/2 wave inverted V and tie it down with fishing line. Nobody will notice it.

28ga copper wire colored black
http://www.parawire.com/28gaugeParaWire.shtml
Old 04-22-2010, 07:33 PM
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Just picked up your post . I work NVIS with a 130' dipole at seven feet off the ground at center and eight feet off the ground at the ends .I feed it with RG8 mini and a LDG Tuner . I have used as little as four watts to check into the 7.290 traffic net ( Amarillo Tx. ) , I live in Palestine Tx.
Old 10-16-2011, 09:25 AM
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Anybody working NVIS? If so, how's it working out and how are you set up?
Successful phone 40 day and 80 night in the Florida Panhandle last night, planning a data test next weekend.

regards,
Endyr
Old 10-16-2011, 04:20 PM
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I use NVIS some times her south in Norway. I have a single dipol around 20 feet high. I can reach more than 200 miles at 80 meter at daytime.

Some times i will take with me a small rig and a dipol out in the field. To save weight i dont use a tuner, only a dipol. When i first started i noticed that i got higher SWR the closer the antenna was to the ground. However when i made the antenna shorter than it should be SWR was back to normal.

BTW in a dessert enviroment you can lay the antenna at the ground or bury it a feet or two.
Old 10-18-2011, 11:37 PM
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Simplex is merely using the same frequency to communicate. In other words, not using a repeater with an offset input/output. Whereas NVIS, skywave, groundwave, longpath, etc. are the physics of radio wave propagation. Apples and oranges.

I've only seen one case of tropospheric ducting, in which FM 2m signals were going 100-300 miles. Check out 6m also. NVIS is an interesting theoretical/physics problem. But if your aim is to reach people greater than 2m and less than HF, that's a more general issue.

Quote:
Originally Posted by killdeer View Post
Being this low on 80 meters allows me to talk to people ranging from 40 miles away to about 90 miles. After that it is not NVIS. and closer than that, it is just plain simplex.
Old 10-19-2011, 07:59 AM
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Recently returning to amateur radio, I put up a 80-10m Windom Wire up about 30' above my house. This might be considered NVIS. I don't have a lot of tall trees near the house. I am only a Tech so 10 meters is where I live at the moment. I also have a Eagle One vertical run to a 6 meter rig. Antenna is sitting on the ground on a hill behind the house, it tunes fine but I don't hear anything. I had the Eagle One on the HF 10M rig and talked a few times within 500 miles so it gets out, just not as good as the wire but the jury is still out. I worked Alaska and Uruguay on 10meters (huge pileup) yesterday on the wire. I also worked much more around the U.S. in the last couple of months. I'm having fun again, upgrade is soon to follow.
Old 10-20-2011, 04:00 AM
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I use a Cobra Ultralite on 40 meters. It's a doublet dipole set up at about 30 feet for NVIS. We have a group of HAMs here on SB that talk weekly. From here, outside of Houston, to Dallas and depending on band conditions all the way to the Ark-Mo state line. So our effective range is 250+ miles all the way to 600 miles

Quote:
I was thinking about hoisting a 40M dipole up the flagpole to somewhere between 10' and 15'. I could only do this after dark and it would have to be taken down when finished. I don't have the room to go 60 or 80M. Any thoughts?
Before I got the doublet so I could work 80 meters, I had an Parr End Fedz 40 meter single band strung up horizontal at about 15 feet high in the backyard. It worked, but not that great. It really depended on the strength of my other contacts antenna set-ups, so it was better than nothing, but thats about it. If thats all I could have, I would have definately looked at some kind of counterpoise to help augment the set-up.
Old 10-21-2011, 11:05 AM
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I use them often as i am RV portable and don't always have a way to set up a dipole at its "Proper" height.

I have a 80m/40m dipole that i set up with the apex that is at 12' to 20' with the end at about 2-3'.

Works well for local and state wide. But dont think that your signals wont go farther. Much Farther. I have regularly worked DX into Europe and South America from the same set-up with 100 watts.

This set-up also tunes well from 80m to 10m with a LDG tuner.

I have not tried to add the reflectors under the antenna yet. That may limit your DX by narrowing the beam of the antenna.


http://www.qsl.net/wb5ude/nvis/

http://www.vcars.org/tech/NVIS.html

http://www.chem.hawaii.edu/uham/nvi40.html

http://www.starc.org/technotes/75-40%20meter-nvis.html

http://www.tactical-link.com/field_deployed_nvis.htm

http://www.dxzone.com/cgi-bin/dir/jump2.cgi?ID=13329
Old 10-22-2011, 07:18 AM
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Sky

I use a Par End Fedz 20M as a sloper top end in a tree 15-20 ft high at a local park and the bottom box stretched out pointing toward the SE from the Phx area and get a friend in Texas on a regular basis if the bands are open. I have not tried it as a NVIS for local comms.
Old 10-22-2011, 07:23 AM
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Hey Cav, do you have a fence in the yard? Try running the wire along that if U got one.
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