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

Dr. Harold Beverage, VP of R&D at RCA had first observed NVIS effects during radio work in Southern Florida with low antennas. A few days before Normandy D-Day the US Navy asked for help providing continuous communications from shore to ship and shore to inland landing forces. He advised them on antenna configuration and recommended frequencies. It worked.

p.s. Beverage was a ham prior to licensing in 1912. He had a 1 inch coil spark transmitter with a range of about twenty miles. He reported hearing the distress work from Titanic, when he was a college student.

Oral History:
https://ethw.org/Oral-History:Harold_H._Beverage

 

Well, in my tiny little country, it happens all the time that I can hear stations thousands of miles away talk to my fellow countrymen, which I cannot hear nor talk to. So I'd like to have an NVIS antenna in addition to my end fed wire.

 

"Cloud warmers," correct frequency, correct time of day, and correct time of year! No magic here!

 

What...is...suppressing...your...GROUNDWAVE?

Of course, if they wanted to talk locally, then they too would use a NVIS antenna...the inference of such high isolation at high angles suggests that is not their OWN preference.

Many hams in the US use modest 160m antennas, which, by physical definition, have NVIS characteristics, whether they like it or not. Thus we talk 'locally', by band-- not by direct antenna design.

No magic, just recognizing a limitation.

73
Chip W1YW

 

I'm orig from ZL, and NVIS daytime on 80m was pretty common among different groups that liked to get together for casual round-table chats in the afternoons, it's great for regional daytime work when the band is quiet and the distances / terrain doesn't lend it self well to VHF or repeaters.

 

Unless they had a high dipole, a modest 80M dipole has high angle radiation component, but is not an intended 'NVIS'...

Just calling a low antenna (in wavelengths) ' NVIS' is not accurate.

What we are saying is some people like using modest antennas that thus have a high angle radiation component-- for example... Inverted V's do this, and are not NVIS.

They are not 'near vertical' only, and thus not NVIS...

I would love to see an INTENDED design incentive for NVIS grounds and NVIS antennas...rather than just slapping an achronym on any old modest antenna at low height.

Lotsa opportunity there for hams for experimentation. Lots and lots!

We have come a long way since RCA's (the company) Dr. Beverage 100 years ago....(BTW I know all about Dr. Beverage, who was an amazing antenna designer and early champion of the Radio Club of America.)

What say?

73
Chip W1YW

 

Interesting, at what distance between two stations is no longer considered NVIS?

 

NVIS has it's place and yes bending the top whip over changes launch angle to allow local contacts. It works because I have used it. Try it and see. I made a wire lip to hold over the top whip and extend it and it attached to my brush guard with some paracord. Part of my mobile go kit now.
You have to be careful discussing it here as its like saying Dark matter doesn't exist. People go nut's and tell you there scientists and your a peon.

 

'near vertical incidence'.... radiation angle

Basically true NVIS defines a cone on the ground where the incidence angle is approaching zenith. The cone diameter is defined by the height of the reflecting layer and the beam--which is 'near vertical'.

Not defined by 'distance'. But in general NVIS works best out to a few hundred km at max. It is frequency dependent and diurnally driven at some frequencies.

 

Haven't seen that.

There scientists...what? There scientists...cross the street? There scientists....take the cinnamon challenge?

'There be whales...?'

Certainly no one should be sticking a shopping cart in a tree to work high angle stuff.

Note Part 97 directly encourages 'enhancement of the radio art'.

Not a peon in site.(pun...)

It would be great if some experimenters felt they can discuss ideas here without resorting only to those found in the 1958 Radio Amateur's 'Ham'book... nor being dissed for espousing said encouragement.

Take care.

 

Take a look at the Military AS-2259 design. Yes, the NVIS is a cool BUZZ word for some and it is another tool in the communicator's world. Still need to have mother nature blessing. I figure hams have been in that NVIS mode for years with low dipoles, etc. with gang buster signals from local to 400 miles +/-. Just couldn't put a name to it.

Military CNR, Combat Net Radios are not looking to to make DXCC in the 30 to 88 mHz spectrum. Couple hundred feet out to 10 miles. Most antennas are folded over for on the move and used that way as not to be a designated target signature device. Lessons learned in deployed countries, running down the street with a 10 foot whips makes for a nice power line detector. Fiberglass or not.

Radio is more that PTT when rolling mobile green.

That antenna on the white rig ??? Codan or Stealth Auto tuned. Very common OGS and Down under and WA6VVC rigs

https://www.l3harris.com/sites/defa...ortable-crossed-dipole-antenna-spec-sheet.pdf

https://www.l3harris.com/sites/defa...03-5-otm-vehicular-loop-antenna-datasheet.pdf

CAMO / WA6VVC

 

This is always a fascinating topic for me.
I was AF Weather when we were using HF for disseminating weather data in austere locations, prior to heavy Comms being brought in. The equipment was given the the name Quick Reaction Communications Terminal (QRCT) in the USAF and Goldwing in the US Army. FYI, the USAF provides all weather support to the Army per the 1947 split. The primary item in the kit was a Transworld "fly away" suitcase transceiver (10W/100W), plus a PC (8088 hah!) and encryption.
The USAF was using the "Train the Trainer" concept at the time. Even if your unit sent their smartest person, and the person had an actual interest, they will never walk away retaining 100% of the instruction. Eighty percent is extremely optimistic. So given the training brought back to the individual units, it was difficult for the average weather guy/gal to make the QRCT work in a deployed location. One particular issue was the data mode was was synchronous and required a robust signal for anything to get through, and I never was able to learn the actual data type. But needing a good signal required the weather pers to visit the antenna system fairly often, especially given the limited manpower at forward (for us) locations.
At some point the weather command hired a Comms expert to run a class at Hurlburt Field that focused on HF radio use. Alan Christinsen was that person, retired from the USAF Communications Agency. As an aside, he also held two patents (5,144,326 and 5,252,985) on the Whip Tilt Adapter for mobile and at halt NVIS communications. He was unable to keep up with the patent, and the heavy hitters in the industry picked it up.
That's all for now, Brian/AF8WX

 

Actually, there is a patent for mobile military antennas to be tilted. Brian/AF8WX

 

When the use of the 60M band was authorized, we used it a lot here in the back country of Idaho as there are few repeaters in the interior.

I figured out a way, using the 108" SS whip on my truck to bend it over at about 45 degrees angle and attach a wire to the end, then using the tuner, get a match on the 60M band.

It worked pretty well, and out to around 400 miles.

That was right after the band became legal to use.

Moving forward to today, I have a Kenwood TS-480 in my truck, and always have the HI-Q antenna on the front of the truck, although it is vertically polarized.

But-I found that if I pulled the 5 foot whip off the top of the vertical portion and using a 3/8X24 bolt in the coil, and attaching a wire, horizontally to the ground, it worked well on 40 and
60 meter NVIS.

Advancing a bit more, I now carry an HF radio, (Yaesu FT-857D) in an old ammunition can with a couple of batteries in a Dewalt DS-300 toolbox
in my Polaris Ranger and the required amount of wire and coax and small solar panel. It only takes a few minutes to setup with the antenna 7 or 8 feet off the ground and I'm on 40 or 60 meters.

Again, with our remote area, and belonging to the county SAR unit and the local EM group, I have used NVIS to reach out to CAP and another SAR operator while on a downed aircraft search and recovery due to lack of repeaters.

From the Ham Radio side, NVIS communications lets me stay out of trouble with the wife by having a friend let her know where I'm camped and when to be expected out.