Image: 6m Moxon Antenna (Click on image for larger view)
With the warmer weather fast approaching in January and February the 6 meter band conditions are expected to start improving, I decided to build an antenna for 6m that will be used with the Ultimate 3 WSPR Beacon. Living in a house with a small back yard I have limited places to mount an antenna.
I finally settled on two antenna designs – the ‘Flowerpot’ coaxial
vertical to monitor the beacon and other 6 meter frequencies and the Moxon beam as a WSPR beacon antenna. Both designs were easy to construct with minimal parts, costs and setup. I will provide more information on the construction of the 6m Flowerpot Antenna in a future article. In this article I will describe how I built my version of the 6m 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 6m Moxon Antennas and ran into an abundance of information which included a calculator.
The dimensions for the antenna were calculated using the free Moxon Antenna Calculator program (available for download from here).
I set my frequency to 50.1 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: 50.1 Mhz (I want to use the antenna for CW and WSPR.)
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 1 meter 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 SO239 Connector (Optional)
2 x Electrical Eye Lug (Terminal)
4 x 12mm Stauff Clamps (Isolaters between boom and elements.)(See images)
16 x 45mm x 5mm Stainless Steel Bolts + Washer + Lock Nuts
2 x 25mm x 4mm Stainless Steel Bolts and 4 x Lock Nut
2 x 45mm x 6mm Stainless Steel Bolts and Lock Nuts
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.
2 x 40mm PVC Pipe End-Caps
1 x 40mm x 80mm PVC Pipe\
1 x 300mm RG58 CU MilSpec 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:
Figure 2:
Figure 3:
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 250mm. I made a mark in the center at 125mm and then two marks 20mm on each side. The first mark on the left is plased 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 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, 2 x PVC end caps and PVC pipe for the feeding point. I will however add several ferrite beads / clips to the piece of co-ax as before installing the antenna.
Just a word on the isolated dowls between the two elements. I left the two 160mm dowls for 2 days in furniture oil to protect the wood from the elements. The oil was soaked up by the dowls and should the dowls last many years to come.
Fitting the dowls to the elements is easy. Ensure there is a 100mm gap separating the ends of the folded elements on each side of the antenna. Lay the two 160mm next to each other and measure and mark the dowl as follows - 30mm - 100mm - 30mm. Mark the measurements with a permanent marker. Ensure that the spacing between the elements is 100mm. Now slide the
dowl inside the aluminium element up to the 30mm mark on one side and also on the other side. You will now have 100mm dowl showing between the elements. I drilled small holes through the tubing and dowl and then
secure them with stainless steel self-tapping screws
Readjust the antenna assembly as necessary to make sure the outer
dimensions are still correct. Once all is OK
Preliminary Test Results:
(Click on the images for larger view.)
I really did not go into a full out testing and using 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 and connect the 6m WSPR Beacon to the antenna. I will provide more feedback and details in future articles about the aim of the project and how the antenna performs. Stay tuned!!
Images: (Click on images for larger view.
