How to Build an AS-2259/GS Antenna
This article is the fifth in a series on Portable NVIS Communication. This series focuses on short-haul communication during a disaster.
In this part, we will build an antenna based on the Army’s AS-2259/GS antenna.
Tools and Equipment Used
- 2 Each, 1.5-Inch x 10-Foot PVC Schedule 40 DWV Plain End Pipe
- 7 Each, 1.5-Inch PVC DWV Coupling
- 2 Each, 1.5-Inch PVC DWV Schedule 40 Socket Cap
- 1 Each, 1.5-Inch PVC DWV H x H x H Wye
- 1 Each, SO-239 Socket (LP UHF-08)
- 1 Each, 500-Feet AWG 14 Solid Copper Wire
- 4 Each, Caribener
- 3 Each, 22-18 AWG 1/4-Inch Stud Loops
- 6 Each, 1.5-Inch No. 10 Machine Screws
- 2 Each, No. 6 Wing Nuts
- 8 Each, 1/2-Inch Brass Nuts
- 1 Pack, 10-Inch x 5/16-Inch Diameter Stakes
- 2 Each, 50 Feet Diamond Braid Camouflage Cord
- Solder Iron
- Phillips Head Screwdriver
Building the Antenna Mast
The mast of a genuine AS-2239/GS consists of seven 2-foot sections of 50 Ohm Hard Line Coax. Most amateurs use fiberglass poles or PVC as a way to reduce cost.
My version with consist of four 3-foot sections and one 18-inch section.
Step One: Cut Four 3-Foot Sections
Using a saw, cut the 10-foot long PVC pipes into four 3-foot sections. Also cut an 18-inch section.
The final 18-inch section mates to the Top Mast Assembly, for a total length of 24-inches. The 24-inch section takes the antenna to a total height of 14 feet, the same as an AS-2259/GS.
If you want to use a balun, make the final section 24-inches rather than 18-inches.
Step Two: Paint the PVC
I chose Army Green.
Step Three: Add PVC Couplings
Add one PVC Coupling to each of mast section.
Step Four: Make Ground Spike
For the other end of the mast, I drilled a hole in a socket cap and inserted a large bolt. This bolt acts as a spike to support the mast when built.
Prepare SO-239 Electrical Assembly
While the paint dries, you have time to build the electrical assembly that will connect the coax to the antenna.
The AS-2259/GS did not have a balun. If you are compelled to use one, skip to the section called Building the Top Mast Assembly.
Step One: Solder Solid Wire Sections to SO-239
First, cut two 18-Inch lengths of 14 AWG wire. These wires will connect the coax to the antenna terminals. Since this version is a low power antenna, 14 AWG is sufficient for 100 watt operation. You can use larger wire if you want more bandwidth.
Next, solder one wire to the center terminal of the SO-239.
Then solder an Eye Loop to the other end of the center terminal wire. This end will connect to the positive antenna terminal post.
Step Two: Solder Eye Loops to Ground Wire
We will fasten the second wire to one of the corners of the SO-239 to create a ground path for the antenna. The other end will ground the antenna terminal post.
Prepare PVC Socket Cap for SO-239
Once the paint is dry, we will install the SO-239 into the Socket Cap.
Step One: Drill Holes for SO-239
You will need one large hole, about 3/4-inch in diameter, to mount the SO-239.
Next, drill four holes to secure the SO-239 to the socket cap.
Step Two: Affix SO-239 to Socket Cap
It should look like this photo once you are done.
Prepare PVC Socket Cap for Antenna Leads
Next, we will install antenna leads into one of the PVC Socket Caps.
Step One: Drill Two Holes in Socket Cap
These holes are about an inch apart and wide enough for a No. 8 screw.
Step Two: Affix Brass Screws with Wing Nuts and Washers
The antenna wires will connect to the other side of this socket cap.
As you can see, there are two screws on each terminal. The additional screws allows me to connect (and secure) four wires to the assembly.
This antenna has four wires, two per band. In addition to being the antenna, the four wires also serve as guy wires to hold the antenna upright.
Building the Top Mast Assembly
The Top Mast Assembly is the business end of the antenna. It is where we connect coax from the transmitter to the antenna wires.
Step One: Insert PVC Couping into Wye
Place one coupling into each outlet of the Wye.
Draw the antenna leads through the Wye and press-fit the Socket Cap to the Coupling.
Step Two: Draw Antenna Leads through Wye
Before you draw the antenna leads, make certain that you prepare the bolts.
I made the mistake of not doing this first, and found it very difficult to mount them.
Then, draw the antenna leads through the opposite end of the Wye.
Step Three: Fasten Antenna Leads to Terminal Socket Cap
Fasten the antenna leads to the terminals on the inside of the Socket Cap.
Press-Fit the Socket Cap to the Coupling.
I would not glue anything together at this point. If you have to make adjustments later, it is easier to do it without PVC cement.
Cut Antenna Wires to Length
As designed, the AS-2259/GS is resonate at 5 MHz and 8 MHz. We must modify the design to make it work on the amateur radio bands without the use of a tuner.
Rather than cut the antenna wires at lengths found elsewhere on the web or make coils, let’s run the math and make our antenna resonant where we want it.
Brian McGinness, N3OC, found that the formula for a quarter-wave antenna 15-feet above ground is 220/f, where f is frequency in MHz.
As I wrote earlier, I have four antennas that I can select depending on the situation.
- 3950 kHz to 4000 kHz for voice communication
- 5323 kHz to 5373 kHz for voice or digital communication
- 7075 kHz to 7125 kHz for digital communication
- 7250 kHz to 7300 kHz for voice communication
Using the McGinness Formula, I calculated antenna lengths for the center frequencies:
- Each antenna element for 3975 kHz is 55′ 4″ long
- Each antenna element for 5348 kHz is 41′ 2″ long
- Each antenna element for 7100 kHz is 31′ long
- Each antenna element for 7275 kHz is 30′ 3″ long
In my next article, I will assemble the antenna, check it with an analyzer, and put it on the air to see what happens.