In this article I will describe how I built my version of the 2m Moxon Antenna.
The
Internet has an abundance of information on Moxon Antennas and I will
not go into to much practical and theoretical detail in this article.
Herewith a little AI information about the Moxon Antenna.
The Moxon antenna originated with British radio amateur and author Les Moxon (G6XN), who published it in his 1993 book, HF Antennas for all Locations,
as a compact, high-performance two-element beam antenna (a radiator and
reflector) with bent-back element tips, offering a great front-to-back
ratio and 50-ohm impedance for easy coaxial connection, based on earlier
explorations of folded-element designs.
Key Aspects of its Origin:
- Inventor: Leslie A. "Les" Moxon (G6XN).
- Publication: Detailed in his 1993 book, HF Antennas for all Locations.
- Concept:
A compact, rectangular variation of a Yagi-Uda beam, using bent ends
(capacitive loading) on the radiator and reflector for efficiency and
size reduction.
- Design:
A two-element antenna (driven element + reflector) with folded tips,
creating a directional pattern and high front-to-back ratio in a small
footprint.
- Precursors:
The design built on earlier ideas, including experiments with
square-shaped antennas by Fred Caton (VK2ABQ) in the 1930s and 1950s.
Why It's Popular:
- Compactness: Occupies much less space than traditional beams.
- Performance: Offers good gain and excellent front-to-back (F/B) ratio.
- Simplicity: Easy to build, often from wire, making it great for amateur radio (ham radio) and field days.
- Direct Match: Its design naturally provides a 50-ohm impedance, connecting directly to standard coax.
In any project one needs a plan, diagram, guidelines and
information. At least that is my way of constructing any DIY Project. I
research the project thoroughly before I start any work. I did exactly
this before I started on this project.
Now the Internet is your
friend but can also be your enemy if you just jump in and start
constructing the first plan you find. I was looking for the dimensions
of DIY 2m Moxon Antennas and ran into an abundance of information which included a calculator.
The dimensions for the antenna was calculated using the free Moxon Antenna Calculator program (available for download from here).
I set my frequency to 145.625 MHz with a wire size of 12mm to represent the
12mm aluminium tubing I was using. The resulting calculation is shown in Figure 1 below.
Image: Figure 1 (Click on image for larger view.)
The Moxon antenna calculator was fed with the following data:
Frequency: 145.625 Mhz (I want to use the antenna for a repeater link.)
Diameter Wire size = 12 millimeters
Transmitter Power = 1 to 15 Watts
After calculating the information listed from A to E were provided.
With all the information now on paper, I was ready to move onto the
next phase and that was to gather all the materials I was going to need.
Materials that I used:
1 x 150 millimeter x 50mm x 3mm Aluminium Flat Bar
3 x 12mm x 2mm x 2.5m Aluminium Round Tube (The thicker the wall thickness the better. 2mm is rather thin.)
1 x 1 meter x 10mm x 2mm Aluminium Round Tube
1 x 1 meter x 10mm Wooden Dowel
2 x 22 mm Plastic End Caps to fit into the 25mm Boom ends.
1 x PL259 Connector
2 x Electrical Eye Lug (Terminal)
3 x 12mm Stauff Clamps (Insolaters between boom and elements.)(See images)
6 x 45mm x 5mm Stainless Steel Bolts + Washer + Lock Nuts
2 x 65mm x 6mm Stainless Steel Bolts and 2 x Lock Nut
8 x 6-16mm Stainless Steel Hose Clamps
2 x Stainless Steel TV - U Clamps
1 x 150mm x 80mm x 5mm Alimunium Flat Plate to mount antenna to boom.
1 x 500mm RG58 CU Mil-Spec Coax Cable (50 Ohm)
2 x 300mm x 4.6 Hellermann Cable Ties
Odds and Sods:Hot Glue Sticks
Self Amalgamating Tape
Solder
Solder Paste
Marine Silicone Sealant
Heat Shrink Tubing
Tools:
Metal Punch
Drill
Various Drill Bits 3mm - 8mm
Hack Saw
Hot Glue Gun
Soldering Iron
Screw Driver (Small flat)
Alen Keys
Spanner Set
Small Pipe Bender (See images)
Test Equipment:
SWR Meter
Antenna Analyzer (If you have one but not compulsory)
Amateur Radio Transceiver
Coax Patch Leads
Mast (Non conductive)
Coax feed line cable 5 m RG58CU 50 ohm
Power Supply for Radio
Building the Antenna:
My final dimensions is listed in the image below:
Images: Figure 2 and 3 (Click on image for larger view.)
I
am not going to go into detail how I constructed my version of the
antenna. I will however describe my findings in constructing and testing
the antenna. The images below provide good detail of how I constructed
the Moxon Antenna.
More information on the build and use of the antenna available at the following sites:
(Click to view website)
My build observations and findings:
Now
how did I bent the 4 elbows of the antenna? I used a small pipe
bender. The 10mm aluminum tubes are cut to 4 x 200mm. I made a mark
in the center at 100mm and then two marks 20mm on each side. The first
mark on the left is placed on the 0 | 0 mark of the pipe bender. Now
start bending until the 0 on the top lever reaches the 9|0 mark on the
bottom lever. You now have a 90 Deg elbow that fits into the 12 mm
antenna element.
To
fit the elbows and hold them in place I used stainless steel hose
clamps. This allows me to easily tune the antenna for a low SWR to a
frequency I want to use. I had two options to join the elbows to the
element. I could have used stainless steel self-tapping screws or the
hose clamps but I opted for the latter.
Mounting
the elements I manufactured 2 x Element Brackets as displayed in Figure
3. I used stainless steel bolts and nuts and Stauff Clamps to install
the 12mm thick elements.
The
last observation and finding pertains to the feed-point and co-ax
connector. No rocket-science here. I used a short piece of co-ax and PL259 + Barrel Connector for the feeding point. I add
a ferrite bead / clip to the piece of co-ax as before installing
the antenna.
Just
a word on the isolated wooden dowels between the two elements. I left
the two 90mm dowels for 2 days in furniture oil to protect the wood from
the elements. The oil was soaked up by the dowels and should now last
for many years to come.
Fitting
the dowels to the elements is easy. Ensure there is a 50mm gap
separating the ends of the folded elements on each side of the antenna.
Lay the two 90mm next to each other and measure and mark the dowel as
follows - 20mm - 50mm - 20mm. Mark the measurements with a permanent
marker. Ensure that the spacing between the elements is 50mm. Now slide
the dowel inside the aluminium element up to the 20mm mark on one side and
also on the other side. You will now have 50mm dowel showing between the
elements. I drilled small holes through the tubing and dowel and then
secure them with stainless steel self-tapping screws
Re-adjust the antenna assembly as necessary to make sure the outer
dimensions are still correct.
Preliminary Test Results:
(Click on the images for larger view.)
I
really did not go into a full out testing and use of this antenna at
this stage. The only testing I have been doing is with the Nano VNA and
a test or two on air RX and TX "excursions". See images above for the
test results.
The
next step will be to install the antenna. I installed the antenna only for test purpose. Two meters above the ground and drooping forward as per image. This was just to check the SWR. I also connected the antenna to my Baofeng UV82 and gave a call on the 145.625 Mhz repeater. Danie ZS1DL returned my call and indicated that there are rain on the signal but that my audio is understandable. Well once the antenna is installed about 6 meters from ground I am certain that I will receive the repeater full quieting at my QTH. Update to follow once antenna is installed.
Images: (Click on images for larger view.
