DIY AS-2259 NVIS Antenna

[Z.O.R.G.]

This is my first "real" post, so I'd like to (hopefully) make it useful. I need to use "HAM Speak" to cover much of it, but will try to explain it so everyone can understand it.


This is my spin on a little known military antenna known as an AS-2259. It's in the NVIS (Near Vertical Incident Sky-wave) family and is used for short range HF (High Frequency or Shortwave) communication on the lower frequency ranges. With a tuner you can use it for most amateur HF frequencies. It consists of 2 inverted "V" dipoles at 90 degrees to each other supported by a center pole with a 1:1 current BALUN (BALanced UN-balanced, check google/Wikipedia for details) at the feed point at the top of the pole. I adjusted the dipoles lengths for the amateur radio bands of 75M (3.8 MHz) and 40M (7.15 MHz) form the original AS-2259 configuration.



How it works: Your transmitted radio signals are sent almost straight up, bonce off the Ionosphere and comes straight back down (Sky-wave). This gives you a circle of communication between 300-700 miles depending on atmospheric conditions. This provides you an advantage over "traditional" antennas as they rely on Ground-wave (signals that follow the surface of the earth) which are degraded by every tree, hill and building between you and the receiver. The dipole legs are used as guy wires for the antenna, and additional guys are not needed


Results: While running 5 watts (extreme low power or QRP) I've been able to overpower 100+ watt stations with "better" antenna systems during contests on the 75 & 40M bands. On 20M (14.2 MHz) , 15M (21.2 MHz) and 10M (28.3 MHz) the antenna behave like a vertical and I've made contacts over 5,000 miles away. As with everything in amateur radio band, conditions are very important and your mileage may vary.




Pros:
Relatively light weight and requires only the center pole for support (If there's a tree or other support available, you can eliminate the center pole and pull the BALUN up with rope over a limb.)
Portable – I've made the center post out of PVC pipe that fits in a backpack making it BOB/BOV friendly
Set-up Time - I can usually set it up in less than 30 minutes by myself.
Excellent short range communication on 75 & 40M – decent longer range communication on 20, 15 & 10M (those are more atmospheric dependent) All Hams want to make long range contacts, but do you really need to go more than 300-700 miles in a disaster/emergency/PAW?
Excellent choice for low power operations – you can get the same (or better) communication with 5 watts as someone running 100 watts, this saves battery life in a disaster situation
It's relatively stealthy – paint or duck tape the center pole in the appropriate manner and it's almost invisible from the ground or air. (As a QRPer I typically use 20 gauge or smaller wire and that's so difficult to see. I usually hang orange streamers on the dipole wires when camping)
Building the antenna system is relatively low in cost and can be done for less than $100.
The center pole can be repurposed to be used as a support for a dipole or as the base of a VHF/UHF ground plane antenna.




Cons:
This is NOT a high gain antenna
Your noise level may be worse due other electronics in the area than "traditional" antennas as it's much closer to them.
75M is primary a night time frequency so you'll have few contacts during daylight hours
It takes up a decent amount of ground area – although I have set it up with the dipole wires going thru trees & bushes.
You need a HAM license to operate one these frequencies (in the US Technician for Morris Code and General or higher for digital or voice) This is not as hard as most people would expect, there are several children under 10-12 in my area that have General licenses.
A good portable all mode QRP transceiver and tuner (Yaesu FT-818, ICOM 705, Elecraft KX3) can cost $1,000-$3,000 new. You can find some Chinese ones, or get something used cheaper. You can also use a full sized radio and dial the power down, but they're not BOB or battery life friendly.
NEVER use bare wire for this antenna. The ends of the antenna have the highest voltage of the antenna and are typically on;y 3-4 feet off the ground, right where someone can get injured by it.


Conclusion: This is not the perfect antenna, but a very useful one for an emergency.

[Z.O.R.G.]

Opp - the attachment didn't make it.   Here's what it looks like.