NVIS - Near Vertical Incidence Skywave

htperry

htperry

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In about summer of 2104 a group of us on the forum experimented heavily with NVIS antennas and use. This is good for comms in a 200 mile radius area that is typically out of range for line of sight (VHF/UHF) comms and too close in for HF "skip". So, NVIS allows you to use HF to talk in that donut that is too far for VHF, but too close for traditional HF. When you see a hummer with the antenna pulled horizontal, that it for NVIS operation (not just storage). I'm game for experimenting with NVIS again. BTW, this only works below 10 Mhz, so is perfect for 40M and 80M.

Think of NVIS as shooting a garden hose to the inside of an umbrella and the water falling back down close-in, rather than a stream of water being shot unimpeded off in a direction. We are using NVIS to shoot our signal straight up and rain back down close-in from atmospheric reflection.


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Lawless and I (he suggested it) were talking about a NVIS net. I would be game to try setting this up too. I could run it along the fence between my yard and the neighbors. Based on geographic location, the three of us could likely bridge a lot of the Charlotte - Greensboro - Raleigh path.
 
Jeepsnguns, georgel and a few others of us experimented a few years ago with NVIS. I use NVIS anyway as part of making contacts. A couple of the former experimenters weren't forum members and a couple of the former experimenter forum members haven't been active in awhile. We can start over and maybe the ham radio contingent will be more dedicated this time. I'm RTG.

I'm trying to move some of my posts from the former forum, so as to save time re-creating the subjects.
 
I just need to find my antenna's and i'll be RTG also. Would be nice to find a very portable setup that works well.
 
Yep, I am ordering a 40m dipole I saw on ebay for like $30 (can't build em yourself that cheap unless you already have the stuff) and will get it set up after Christmas. I think it would be great to have a NVIS network of folks from here and to have a reliable way to communicate if things were bad. Howard can pick us a good 40m freq and we can give it a go.

trcubed you in Terry?
 
I think I have the stuff to make a NVIS setup out of firesticks. If it works, would make a really nice portable setup. Based on how they work as verticals, i'm not hoping for much.
 
Lawless;n23237 said:
Yep, I am ordering a 40m dipole I saw on ebay for like $30 (can't build em yourself that cheap unless you already have the stuff) and will get it set up after Christmas. I think it would be great to have a NVIS network of folks from here and to have a reliable way to communicate if things were bad. Howard can pick us a good 40m freq and we can give it a go.

trcubed you in Terry?
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Sure. Let me know when and where.

I have a 20M dipole in the attic that should work 40M (need another feed line), but the end-fed inverted L in the back yard might work even better.
 
I just dug thru my back shed and found my NVIS pile. Now I just need to find some coax. Mine is either running up the tower or thru the attic right now.
 
trcubed;n23296 said:
Sure. Let me know when and where.

I have a 20M dipole in the attic that should work 40M (need another feed line), but the end-fed inverted L in the back yard might work even better.
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20m dipole is too short. Extend it to 66 feet and you'll be good. You'll need reflector wires, too.
 
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htperry Snal~

I found a spool of 16g green automotive wire a few minutes ago in my barn I had forgot about. I also have a partial spool of TV coax (big orange direct burial stuff) that I think is 75 ohm. Now, a smart feller might suspect he could home brew an antenna for about free. If I order some of these for the radio end of the coax and solder the wire at the antenna end to the coax, use home made insulators and such...

Any reason my tuner won't make this work for our NVIS experiment?

**edited, I just read that this RG11 cable has aluminum shielding and is a pain to connect to PL259 connectors and is not able to be effectively soldered.
 
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Yes, that would work. You can connect the radiator elements directly to the coax. You can use 75 ohm coax with very little impact. That's only a 1.5:1 mismatch and your tuner will clear things up. It'll work just fine as an example of improvised antenna.
 
For a field antenna, I find the endfed to be the most practical, by far. Simple, easy to use and useble in multiple configurations, vertical, inverted V, sloper, etc. My homebrew mono- band 40m endfed, set up in an inverted V was out talking my G5RV in to Maryland to a then forum member. Howard was part of that qso. Then that same antenna, set up at 7ft. as a flat top NVIS. with a single reflector was talking in to middle TN at s7 using a mono-band qrp rig at 10 watts.
 
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I tried to organize a forum ham radio net about 3 years ago with limited success and in recent times to compile a forum ham directory with next to no interest. Maybe this time is a charm. I'm along for the ride. I'm very comfortable in my ability to communicate at will. I hold up my end of the two way street.
 
Hi guys,

I've been a ham operator since 1983. What most hams never realize is that NVIS occurs just about anytime when using a horizontal wire antenna that is below 1/4 wavelength above ground. So for 40, 60, 80 and 160 meters, a simple dipole or multiband doublet (open wire fed non-resonant dipole) will perform exceptionally well. I have two horizontal antennas I use. One is my 235 foot doublet mounted as an inverted vee with the apex at 40 ft and fed with 300 ohm ladder line. This antenna requires a tuner, but covers 160 thru 20 meters easily and up to 1500 watts. The other antenna I use on the lower bands is an Off center fed dipole. One leg is 45 feet long, the other is 90 feet long with a 6 to 1 balun at the feed point. Coax fed rated for 1500 watts and SWR is 3 to 1 or less on all bands so a tuner is not really needed. It too is mounted as an inverted vee and the apex is at 40 feet. I use these antennas daily to work stations all over the Southeast depending on band and conditions. For Daytime 160 meters gives the shortest range, 80 meters easily covers both the Carolinas, 40 meters gets you most of the Southeast region. At night those ranges expand out to worldwide. 99.9 percent of the time I run only 100 watts from the radio. Just my experience over the years. I've tried specialized antennas for NVIS and haven't found them to work any better than what I just described. Anyone wanting to play, send me a message and we can get on just about any time or day. I am semi-retired and available most days and times except Mondays and Tuesdays.
 
Almost all 80/160M antennas and many 40M are NVIS due to their height. However, while many operate mostly NVIS, more are not optimized for NVIS. What we are suggesting here are NVIS optimized operation.
 
For me, the target is field capable regional communications. The concepts of NVIS fits this need. There are a few configurations of NVIS. Some are so onerous, it's like, why bother? Might as well put up a regular antenna. I abandoned the military AS-2259 because it was going to take up too much space and require carrying too much gear to put up. It has to be modified anyway to work on the ham bands. So, don't go buying one surplus thinking it will work well without moding. For a semi-permanet installation it might be cool.
 
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georgel;n25300 said:
For me, the target is field capable regional communications. The concepts of NVIS fits this need. There are a few configurations of NVIS. Some are so onerous, it's like, why bother? Might as well put up a regular antenna. I abandoned the military AS-2259 because it was going to take up too much space and require carrying too much gear to put up. It has to be modified anyway to work on the ham bands. So, don't go buying one surplus thinking it will work well without moding. For a semi-permanet installation it might be cool.
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My online friend Brushbeater is in Durham area and is a whiz on portable NVIS on higher bands. His blog has lots of info if you go back a ways.
https://brushbeater.wordpress.com/
 
Lawless;n25286 said:
Raider21 the OCF antenna at 40', how close in will it do on 40m?
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georgel and I were less than 10 miles apart, Jeepsnguns was QRP on the beach at the Outer Banks and NC3Z was in Maryland at the time. We all talked at will during the day. I used to talk mobile-to-mobile to NC3Z on 40M regularly. I don't think Gary has made it over here.
 
This writer is considered by many to be the NVIS guru. She died a few years back but this paper is still online.
Attached PDF.

 

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Lawless;n32331 said:
This writer is considered by many to be the NVIS guru. She died a few years back but this paper is still online.
Attached PDF.

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This was one of the first articles I ever read on the topic and got me interested in NVIS.
 
What is an affordable way to get into HF that I won't feel like I threw my money away in just a few months? Maybe one of the homebrew kits for just one band?
 
Cape Fear said:
What is an affordable way to get into HF that I won't feel like I threw my money away in just a few months? Maybe one of the homebrew kits for just one band?
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I will let Howard or John answer the specific question, but a used Kwood HF radio or similar can be found for $300 or so. Of course then come the tuners, antennas, cables, ect..

A good 100' piece of coax is $100...
 
Cape Fear said:
What is an affordable way to get into HF that I won't feel like I threw my money away in just a few months? Maybe one of the homebrew kits for just one band?
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Which Kenwood radio did you go with? I had picked out the Kenwood TM-V71A for my first desktop mobile station but now I realize it won't get me into HF.
 
I'd suggest a used TS440 or IC718 or some such. Solid performance you won't grow out of quickly and affordable 100 watt all band./mode radio.I'd try to find one locally that you can see work. I'd estimate 300 -500 $ for a decent rig. IC706 might work too.

What say Howard?
 
Cape Fear said:
What is an affordable way to get into HF that I won't feel like I threw my money away in just a few months? Maybe one of the homebrew kits for just one band?
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I got a nice Kenwood TS430s. The 440 and up is a little nicer as the tuner will communicate via cable interface.
 
OK, I have my new OCF at about 25'. Ready to get the NVIS net up and running. It may not be perfect for close contacts but i bet it works pretty well.
 
JohnFreeman;n42613 said:
What say Howard?
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Sorry I missed this question:

Icom IC-735/745/718
Kenwood TS-430/440/450 TS-50
Yaesu FT450 FT-857D FT-850/900 FT-100D (FT-817D for backpack QRP)
Alinco DX-SR8T (great value brand new)

There are actually many inexpensive (relatively speaking) good older HF rigs. Any used radio can come with issues. If you don't like taking chance, buy new. One of the best new values is the DX-SR8T Alinco @ under $500. If I were buying new on a budget, I'd probably buy a Yaesu FT-450. I'm radio agnostic, not a brand whore, and like them all.
 
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