Early on in my ham radio adventure (and still to this day), I was very frustrated with the fact that I could never do DX on 80 and 40 meters. I mean, wasn't the whole purpose of ham radio supposed to be how far you could be heard?
In the past few days, I realized that I had actually unlocked an HF cheat code all this time. I've been using the bands wrong. Here's how.
Near Vertical Incidence Skywave
Otherwise known as cloud warming.
NVIS is NOT a type of antenna. It is a type of antenna radiation pattern. Instead of a low takeoff angle which is favored for DX, NVIS propagation shoots straight up, usually between 60 and 90 degrees, with 90 degrees being favored.
I always was told that to operate DX, the antenna needs to be up as high as possible. 15 feet was as high as I could get without upsetting the landlords (my parents, hi). I couldn't complain, in fact I was just grateful I could get an antenna up!
However, I was SEVERELY disappointed with the results on 40 and 80 meters. I could only get out across the country, sometimes even only within the state. I wanted across the sea!!! Boy did I throw a fit. Little did I know, the antenna was doing its job just fine. No fault to the antenna, fault to the operator.
What I was experiencing was NVIS - Near Vertical Incidence Skywave. It's basically a fancy term for using the ionosphere to bounce HF radio signals back down regionally. So yes, anywhere between 0 and 500 miles is to be expected. But why would us hams need to use NVIS? Going a limited amount of miles seems counterintuitive, maybe even a bit dumb.
Actually the reasoning is quite simple, and it's quite beneficial in emergency situations.
Wait...What???
Yep. In an emergency situation, NVIS is the answer. Here's why.
NVIS is what most ARES and RACES agencies use to communicate. Generally, if you need statewide or even countywide comms, NVIS is the way to go. Let's take for example a really mountainous or hilly terrain.
Now you could use VHF and UHF, but only if there are repeaters on the tops of the mountains. If you're in an emergency set up, someone could set up temporary repeaters but this wouldn't make much sense if EMCOMMs are supposed to be expedient in setting up and tearing down. Ground waves could also become an issue as well. Ground waves are waves that actually travel on the ground. Dense foliage, particularly in the Vietnam War, proved to be troublesome, and the US Army found that densely foliaged areas could provide only a mile or less of ground wave propagation. So it's possible, even likely, that we can't even use the curve of the Earth either.
The answer is NVIS, yet again.
In all cases, NVIS can access those skip zones that DX just grazes over as well. It truly could be called the missing link. This includes crucial contacts for statewide nets, emergency coordinators in the next county over, and many more places where VHF/UHF seems logical but may be beyond unreliable.
Or, let's take the NAQCC Midwest net, held every Monday evening at 7:30pm CST/8:30pm CDT. Net control is located in Leawood, Kansas. From Maryville (as the crow flies), that's a little under 100 miles from me. Obviously, if I used a vertical or any other DX-capable antenna, I would greatly overshoot this and wouldn't even get a check-in. Perhaps I would if I'm using ground wave, but I highly doubt this would work the way I'd want it to. Of course, I could have a fellow in some distant land relay me in from over 2000 miles away but that wouldn't be very effective.
When I was first setting up my ham radio station, I purchased a Chameleon CHA TD LTE dipole, which works with a tuner between 160 meters and 6 meters. Chameleon advertises this antenna as a rapid-deployment type, suitable for ARES, RACES, and even mentions its outstanding NVIS capabilities.
Testing
For testing NVIS capabilities, here is the test I propose:
First, we'll start with daytime bands. For NVIS, frequencies between 4 and 8 MHz are used primarily during the day and between 2 and 4 MHz during the night. During the day, I will test 60 meters (using CW and the RBN system) and 40 meters. As a bonus I'll also test 10 MHz during the day since this is the borderline NVIS frequency. At night, 160 meters and 80 meters will be the primary bands I test.
For the antenna, I'll use the Chameleon antenna set up in an inverted vee or regular dipole, tuned up with an LDG Z-100+.
Tests will be ran using the WSPR protocol, starting with 5 watts (the lowest the 891 will go) and will bump up to 20 watts at a maximum. The only exception will be 60 meters, in which I will use CW on the old Channel 3 frequency, 5358.5MHz. Reporting data will be collected from wsprnet.org and 60 meter results will be collected from the Reverse Beacon Network, hopefully.
Daytime Tests
40 Meters
60 Meters
30 Meters (Bonus)
Nighttime Tests
160 Meters
80 Meters
The Plan now
- 160 Meters - NVIS using Chameleon
- 80 Meters - NVIS using Chameleon (possible DX with the vertical and coil?)
- 60 Meters - NVIS using Chameleon (possible DX with the vertical and coil?)
- 40 Meters - NVIS using Chameleon, DX using collapsible vertical and loading coil
- 30 Meters - NVIS using Chameleon (if successful), DX using vertical and coil
- 20 Meters - DX using vertical or Chameleon
- 17 Meters - DX using vertical or Chameleon
- 15 Meters - DX using vertical or Chameleon
- 12 Meters - DX using vertical or Chameleon
- 11 Meters - Use the vertical, not sure about DX on 4W AM :)
- 10 Meters - DX using vertical or Chameleon
This plan seems reasonable given the circumstances that I'm in and the equipment I already have. The benefit to NVIS operation for me is that my antenna height is adjustable up to 15 feet, so if I'm not getting to the place I'd like to, I can change the antenna's height. If I want it as low as 4 feet, I can lower it to 4 feet. 10 feet? You got it!
A general rule of thumb: as long as your antenna is well under a 1/4-wavelength above the ground, you'll be shooting NVIS.
Drawbacks
Because it's not ham radio if there aren't any quirks.
First, NVIS antennas require that you and the other station both have NVIS-oriented antennas. It'll work if one has an NVIS and one has a DX-oriented antenna, but your signal strength will be significantly weakened in comparison to the both of you using the same antenna orientation. In some cases, you might not be able to hear each other at all. It could be the difference between S5 and S9+.
Second, ground loss is somewhat certain with this antenna. The ground is used as a reflector in this set up. If you're worried about ground losses, you can run a reflector wire that's 5% longer than the main element directly below the radiator. Kinda similar to a vertical yagi!
Lastly, selecting the correct frequency is critical. In fact, there is something known as FoF2 - the highest frequency that returns to Earth when transmitted upward. If you attempt NVIS on the wrong frequency at the wrong time of day, there's a good chance your signal will actually penetrate the ionosphere and go to space.
A REALLY Cool NVIS Antenna Idea
If you think this is cool, what if I told you that you can operate NVIS away from home using a single piece of wire?
If you have a metal-bodied vehicle, you can run a 1/2-wave long wire from the center of a 3/8x24 stud and use your vehicle as the ground! You could use this for camping, roadside breaks, or anywhere where you may be mobile! Stephen Reynolds, W4CNG, offers a really good write-up from 2002 on how to construct such a device. You can find it on eHam here.
Additionally, K6SOJ offers a similar write-up on HamUniverse.com. Much similar to Stephen's idea, however he suggests that you use 2 lengths of 33 foot wire - just connect the additional 33 feet to the pre-existing 33-foot 40 meter section for operation on 80 meters! You can find that article here. This one is cooler because he's installed his setup on a Toyota Land Cruiser.
What's even better? If you don't want to permanently install a bulkhead connector on your vehicle, you can use an old magnet mount. Just attach the antenna wire to the center pin of the mag mount and you're done!
Applications
I have identified at least one ARDOP Winlink station within NVIS range of me. It's located in Columbia, MO and operates on both 80 meters and 40 meters. This is due southeast of me. Sadly this is the only ARDOP station I could possibly reach using NVIS.
VARA is a different story. South of Omaha, there is a VARA station that is active on 80 and 40 meters as well. Near Fremont, NE lies another 80/40 VARA station around 100 miles away from me that also uses NVIS. Finally, there is yet another VARA station near Overland Park, KS.
Not to detract from the current topic, but it boils my blood that VARA is only supported on Linux via wine. There's more than one way to skin a cat but for Winlink, it's both time-consuming and frustrating. Hopefully I'll find a reasonable solution soon...
I have had great success with Winlink operations using even just 10 watts and my bedroom random wire. You can most certainly bet I will be using NVIS if I need to send email over RF. In addition, HF packet radio is something else I hope to try, and around me, there are at least a dozen HF packet radio stations that are certainly reachable!
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