ANTENNAS HF and NVIS Communications .... only for the Military?

HF stations have employed NVIS antennas in Australia (and elsewhere I am sure) to take advantage of this propagation for quite some time, even if the operators did not know they are using NVIS propagation.

Many civilian mobile stations in remote areas of Australia routinely use this propagation method to permit shorter distance communications (beyond ground wave) to communicate with stations that would be otherwise in the skip zone. Low hung wide band antennas were installed at many remote stations in years past to make use of this propagation to ensure reliable communications at distances up to say 500km.

I am no expert but, I do not believe that the implementation of all radio communication methods within the military is taught to all. Most service personnel will only have a good knowledge of what they require. I am sure someone from a signals corps background would be able to confirm the use of NVIS in certain military situations, both mobile and fixed.

Cheers all. Stay safe

Peter VK4XO

 

You guys are cracking me up ... and wait-- So how do you pronounce GUI? Gee U eye ?

 

It fits in nicely for our "60m Q's from SFO to Santa Maria,CA and from SFO to Reno"..hi

 

I always thought it should be pronounced envious, as in envious of those who have higher trees to get their antennas away from the ground.

And my GUIs were always gooeys.

 

I literally laughed out loud... love it!

 

Although it is much easier drive the vehicle without breaking the antenna it it is folded ;-) , the main reason to do this it is because of reflection on ionospheere as it was described on the article.
The military radio manuals like "Clansman - PRC 320" explains this to be used for short distances. An example of use is to keep the radio contact between vehicles in convoyes.

 

I keep seeing people write this... but in my first hand experience, it doesn't work. The antenna, when properly tuned while vertical and NVIS position over the ground, had an SWR greater than 30:1 while over the body of the truck and is not tunable.

Also, I haven't been able to adjust the length of the antenna to get it below 5:1 over the body of the tuck, and even with a tuner, I can't make a single contact unless the other radio is within a few hundred yards. Even at 100w. And when the antenna is cut for best performance over the truck (which is terrible), when the antenna is vertical or in the NVIS position over the ground, the SWR is greater than 30:1 and 100% unusable.

 

Almost forgot... the Clansman - PRC 320 is a backpack radio. Not sure what that has to do with mobile NVIS.

 

Whatever you want to call it... NVIS as been around a long time. This is just one book on NVIS on my bookshelf. Trained and fielded. QRP / manpack operators take note.

https://brushbeater.files.wordpress...ave-communication-book-worldradio-books-2.pdf

Practical tactical task and purpose HOOAH WA6VVC / WA6CAM

 

I am always looking to learn and improve. So, I have a question for you (or anyone else who can answer it). This picture shows the radiation pattern with the whip tied down. There is plenty of description of it working in the document.

My question is, why does it not work on my vehicle with my setup? Is it because I am using civilian hardware, compared to the Harris base, so I can't possibly tune it with my gear? Is the whip just too close to the body? I'm looking for a real/scientific answer so I can get repeatable results.

 

Something a little more recent....
https://apps.dtic.mil/sti/pdfs/AD1039223.pdf

 

Yes.

See Fig 31.

 

No idea why you cannot get your setup to tune. I am running a SD330 mounted high up on the side of my van just behind the drivers door. I can pull the whip over diagonally across the roof line to the front and it tunes every band the antenna is capable of in its normal position. Used to do it with a 9' whip mounted similarly but on the left rear corner. Never tried mounting center or right as trees can be an issue. Hardest part of seeing usefulness is contacts. I did most of mine on a regularly scheduled net where I knew the locations of the other stations. Various locations I was in amongst the NE mountain ranges showed me it could be useful under certain conditions and locations. My home NVIS worked wonders during local ragchews which got me into playing with it mobile.
Not knowing your setup on your vehicle leaves a lot of questions.

 

I did a whole write up on my mobile setup earlier in the thread, if that helps.

I'm shock the SD330 is tolerating the pressure from having the whip pulled over. Mine didn't survive more than 3 months before the gears were shot, making the coil worthless. And that was with the factory whip. I can't imagine a 102" or 108" whip not killing it in a few days/weeks.

 

Near two years on mine. I extend the whip with a cable so as not to put much pressure on it. Haven't tried it on anything above 20 in that configuration. I don't understand so many having failures but my best guess is related to mounting. I use a 4" breedlove so-238 ball mount. It is solid but its on a heavy van and sees a lot of punishment with potholes an unimproved roadways. Now when I do the NVIS thing I am 99% stationary. Being my first foray into screwdrivers I didn't want to spend near three times the cost to try it. If it does fail I will probably replace it with the same considering the use I got out of it for the price.