NVIS Antenna

[Lawman51]

We used these in the military and got pretty good results for the medium range transmit region. I have been looking around and have found a design I am planning on building and just wanted to know if anyone has built their own NVIS antenna and how they liked the performance, any issues that were unexpected as the build went along..

 

[PACNWDude]

NVIS antennas.

My first experience was during military service as well.

We build bases out of plywood, coated in bed liner. Then mounted the antenna on top and bent it over.

CUCV's had whip antennas and we would bend them over to get NVIS operation as well.

I have not built one since those days though, has been about 15 years.

 

[prcguy]

I've made dozens and dozens and maybe more NVIS antennas with a couple of designs published out there. I also spend quite a bit of time in the field testing and playing with them, usually fed from a military HF manpack rig or an Elecraft KX3. Since I'm at or near QRP levels my antennas have to work well to make up for the flea power and they usually do that very well.

The basic criteria for an NVIS antenna is something that gives an upward lobe within the frequency range that NVIS propagates, which can be from a very low frequency to about 10MHz depending on propagation. Most hams with a horizontal wire antenna already have an NVIS antenna and don't realize it.

The most gain for a horizontal dipole or similar antenna is about a 1/4 wavelength above ground and for most people the 40m band is about the highest band you use, so about 33ft would be the highest height above ground for a 40m NVIS antenna or a multi-band NVIS antenna. Go lower and you start to reject distant signals arriving at a lower angle, but your upward gain starts to fall off rapidly.

Here is a mock up brochure for a multi-band NVIS HF antenna I designed with a separate mount and ground radials for an NMO VHF/UHF mobile antenna on top. Look at post #3 in this thread which has the description and brochure: http://forums.radioreference.com/am...able-antenna-recommendations.html#post2339024

This is similar to what you guys probably used in the military but much more lightweight and versatile. With all that said, what design has the OP decided on?
prcguy

We used these in the military and got pretty good results for the medium range transmit region. I have been looking around and have found a design I am planning on building and just wanted to know if anyone has built their own NVIS antenna and how they liked the performance, any issues that were unexpected as the build went along..

 

[Lawman51]

This is the initial one I was looking at building. http://static.dxengineering.com/pdf/WP-NVIS-Rev2.pdf After looking at the one you built though I think it would be more useful for my intended purpose as I am getting built up for our area RACES team. I like the idea and utility of the 2m/70cm vertical with the ground plane incorporated into the NVIS design...does not appear to be too much extra to the build just have to plan a little more. I am going to be using this with the 857d once I get the test passed in January for my General.

 

[Lawman51]

My first experience was during military service as well.

We build bases out of plywood, coated in bed liner. Then mounted the antenna on top and bent it over.

CUCV's had whip antennas and we would bend them over to get NVIS operation as well.

I have not built one since those days though, has been about 15 years.

I was in late 80's to early 90's. We had the turtle back hummv's and were always out in squad size (3) trucks that were required to cover large areas 10km boxes to each truck and figured out nvis on our own by mistake due to the German Government yelling at us for banging up the undersides of the bridges...lol The maint. plt told us not to transmit with them in the bent over position, but you know a solider tell them not to do something so they have to figure out why. Tried it just to see what would happen and ended up contacting a unit that was in norway and we all decided right there we were transmitting that way for distance comms....comms nco never told us...so I volunteered to go be the com nco for our plt...that is when I really got in to radios and antennas.

 

[prcguy]

If you have the space its hard to beat a maypole type antenna where the wires and guy strings hold the antenna up and no other guys are needed. The Buddipole mast I used is a 16ft version which puts the feedpoint around 18ft, but I would go with the newer 18 ft version or I've seen similar types in the 25-30ft range if you can find one. The Buddipole mast is nice because it terminates in a pipe thread which is great for a PVC pipe compatible project.

If you want to give up the NMO mount you can use one of the popular 33ft telescoping fiberglass masts, then drill a 3/8" hole through the top PVC pipe cap at the feedpoint and slide the whole PVC assembly over the fiberglass mast until the tapered mast jams into the 3/8" hole. That will put the feedpoint in the 28-30ft range and bring up the efficiency a little on the lower NVIS bands and the upper bands will also perk up for DX.

For use on bands other than 40 or 80m you can feed it with 300 ohm TV twinlead and it works great for DX on 20 through 10m.
prcguy

This is the initial one I was looking at building. http://static.dxengineering.com/pdf/WP-NVIS-Rev2.pdf After looking at the one you built though I think it would be more useful for my intended purpose as I am getting built up for our area RACES team. I like the idea and utility of the 2m/70cm vertical with the ground plane incorporated into the NVIS design...does not appear to be too much extra to the build just have to plan a little more. I am going to be using this with the 857d once I get the test passed in January for my General.