Building the Moxon Antenna

Since the main page picture is a 10m moxon I thought I'd better show you how it was first built. I’d would have loved to have a yagi for a bit of directional activity, but unfortunately I didn’t think I would get the official stamp of approval so I had been pondering what else I could use similar to a yagi.

 

I did some searching on the web and came across the Moxon Antenna which looked to be just the job and fairly easy to build. I didn’t fancy the standard wire antenna with the cross support poles, I wanted something a little sturdier, and found this website which describes all the details for constructing a tubular Moxon including the Moxgen software for working out the dimensions.

I inputted the information but setting the thickness was a bit tricky because I had different aluminium tube sizes throughout the rectangle (bought on the cheap from the local hardware store). Bending the tubing proved interesting but I managed to borrow a small pipe bender that proved very useful. Eventually I set it at an average of 12 mm on the Moxgen calculator thinking that if I overestimated I could always trim. (Better to have the length than it being too short).

I got to the stage that the rectangle has been built and I had used an old TV antenna as the boom and pinched the plastic feeder complete with circuit board, but when testing I think I had over complicated the build so I removed the TV feeder (the circuit was shorting) and literally just attached the end of the coax using jubilee clips to each side of the antenna. First results showed the SWR to be very high at 28.100 but an acceptable 1.3 at approx 26.500 so some trimming was required.

Having done further checks on the thickness of the tubing I soon realised I had over compensated. The tubing was a mixture of 8, 10 and 12mm with the majority being at 10mm. So I recalculated at 10mm and of course my original dimensions were slightly out, hence the high SWR. So I dismantled the rectangle and began to re-trim to the correct lengths for 10mm, lets hope that makes the difference, I’m informed that the space between the reflector and driven elements are very important so I had to make sure I got that absolutely correct;

 

Update on the Moxon Build

Finally it was completed with a mish mash of bits and pieces mostly nicked from the junk box. The only expense was the tubing and two plastic garden stakes for the spacers which I got from a local hardware shop for the princely sum of £24.00.
The SWR readings were spot on at 1:2:1 from 28.050 right up to 28.450 which did nicely considering I’ll was for using it for CW
A few pictures below; two from the beginning of the rebuild when assembling the old TV boom and making the reflector and one of the finished product in the advancing evening dusk (shows how keen I am)!

Dismantled after the first attempt where I re-calculated the dimensions, the centre block is an old bread board.

 The join for the reflector, a simple bit of carpentry an some jubilee clips

The finish product in the evening dusk, not bad for a days work!

A final view from above!

Well I did some more testing and it worked as it should so then having connected it up to the FT1000 and fired it up, it was a definite improvement on 10 meters against the cobweb, especially with the Moxon pointed west where the US stations were booming in. The other good news was that with the ATU on the Yaesu I could add 12 meters and managed to have a good CW qso's with a Russian station that gave me a 579 and then a Japanese station who came back with a 589. The plan now was to find myself a light weight TV rotator and have some fun spinning it round!

 

Moxon Update

 

Building the moxon has certainly given me an appetite for beam antennas. Having managed to get hold of an antenna rotator the moxon has definitely proved itself and I have been having great fun especially with early morning contacts to VK, ZL and J stations, I even had a BA over the weekend.

 

 

 Looking good but before I'd got the rotator

The rotator was bought from Conrad Electronics for £49.00 and is a standard TV rotator, but ideal for something light like the moxon. The only problems I faced were that the instructions were in German (my German is not good), and so in my haste I did not realise that the separately supplied 3 pin plug just allowed the European 2 pin plug to just slot in to it. I thought I had to rewire and so I cut the 2 pin plug off..........oops! A quick bit of reconnecting and soldering fixed the problem and I soon had it all attached to my mast and was rotating away to my hearts delight.

Whilst building all my antennas I borrowed an MFJ antenna analyzer from my brother in law, he now wants it back as his Hygain came down in last weeks storms and he needs it to reset the vertical. Without an analyzer I feel slightly lost and so I took the plunge and bought a Feature Tech AW06A which is a basic analyzer covering just the SW frequencies. The few reviews I’ve managed to read give it a good write up and compared to the MFJ is fairly basic, but it should do the job. Fingers crossed I will receive it before Christmas and I will give it a proper write up in a later post.

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 Seventeen or Twenty Meter Moxon 

14/12/2016

I've taken the plunge and decided to attempt to build either a 17 or 20 meter version of the Moxon. I had so much fun building the 10 meter and realised how much gain and direction you can get plus it's a lot cheaper option than trying to buy a Yagi.
The reason I say 17 or 20 is because of size, whether it will fit in with the surrounds and not take over the paddock. So I'm going to have to measure up and see how things will fit!

The twenty meter version is nearly 8 metres across so it's fairly big and obviously the 17 meter is not that much smaller. Two factors will need to be ticked off, the XYL's approval and the locals in the village passing by in their cars not being able to notice without a really good look, so a bit of camouflage will be needed! To be honest I like to go for the 20 but we'll just have to wait and see.

At some stage I'd like to have a Hexbeam but at the moment I don't have the time or money to either build or purchase one so I'm going to settle with another Moxon only bigger this time!

I won't build as the 10m with an aluminium rectangle, I'll just have a boom and the wire elements, adjustable GF fishing poles as the spreaders. I have four spare 8 metre telescopic fishing poles and have two 2 meter aluminium booms which can be added together if necessary. I also have the mast to boom connector ready made up so the completed antenna can be fitted to a rotator or mast as required.

I was going for the boom and centre plate with the four poles out at an angle shaped as a criss cross, but after looking at various options I felt the H shape with the fishing poles at either end of the boom looked a little stronger. The reflective and directional wires will run through the poles and only be exposed at each end for the measured gaps. Basically it will be based on a design by a German Amateur DL7AOS, although his antenna is a 20 meter version, but if I have to choose the 17 meter version I can adapt. He's done a very simple but effective build.

 

Funnily enough there was a written account of a 20m Moxon in this month Radcom which is the RSGB's monthly magazine. So I may pinch some ideas from that as well. I'll write further as the build develops and add some pictures.

 

Well in the end I've gone with the 17m version simply because of the size and the area it has to fit in to. Living in an area of outstanding beauty you have to watch the neighbours, they can be very fussy and sometimes I'm amazed at what I can get away with!

So beginning the build, I started on the cross member of the aluminium boom which will hold two of the fibre glass fishing poles. These are simply screwed and fixed to the boom at each end.

 

Having added the cross members to the boom, the fishing poles are attached with plastic ties, these are 5m fibre glass fishing poles at each side and the directional and reflective element wires are fed through. There is a small box at the directional end of the boom to house the coax connection and the two front elements wire. A note of caution, I used PVC coated stranded speaker cable, although 1mm thick which I added to the calculator, remember to take in to consideration the PVC. (explained more later).

 

 

 

The fishing poles are so light, the plastic ties will be fine for holding to the boom frame. Below is the front end nearly completed apart from stretching out the fishing poles.

 



  The easy bit was constructing the frame. Providing you follow the measurement rules on the Moxon website you can't really go wrong, plus there are loads of construction examples to choose from.

The tricky bit is getting the separation of the director and reflector wires the right distance, but again the measurements are all in the calculation tool on the website. So it's a case of measuring up twice and working on the antenna once!

The SWR is rubbish when set at low height. you'll find as you raise above 15ft things start to change.
At first I was testing at about 10 feet and my SWR was awful but then raising I got some results, peaking at 1:2 at 17.400. I thought I'd really screwed up on something. After avidly reading up on the Moxon forum, I raised the antenna and the SWR still looked no better, At 20 feet I got 1:9 at 18.100, rising to 2:0 at 18.160. It certainly needed a trim!

While we are at it below is a picture of my Delta loop for 20m, but this will come down to be replaced by the Moxon when its completed. The 35 foot mast is a tilt over, so adding the Moxon should be relatively easy, plus at a later date when I have some 5 core cable I can add to the rotator.
 

 

I also added a picture of the 6m dipole I made a few months back, I've since  removed to add the Moxon for testing but it looked rather good in the sunlight and early morning frost, sitting there in its rest position on my fibre glass 20 foot pole

Ok Digressing there slightly back to the Moxon, I took it off the temporary mast and prepared the main mast which was 35 feet, consisting of a 30ft mast and a 5ft added section. I raised the mast with the rotator and antenna and found a considerable bend in the scaffolding pole but once up was reasonable but any breeze and it began to move even with my four guy ropes.

 

About to remove the 5 foot section

Deciding to be cautious and to not have any accidents I shortened the mast by 5 foot removing the added section, although now only 30 foot it didn't seem to effect the antenna too much.
Happy with the set up I then turned to the SWR which was now reading a 1:2 at 17.185 and a 1:9 at 18.068, getting higher to 2:2 at 18.130. Taking the 17.185Mhz as a template I trimmed the director by 150 mm and the reflector by 50mm, this brought down the SWR to 1:2 at 18.100, perfect for my needs! the difference was because I hadn't added for the PVC coated wire I was using (42 stranded speaker wire) you have to be exact for the Moxon calculations.

The completed antenna

 

Having now completed the Moxon and spent all of Sunday having a play, I am very pleased with the antenna. I certainly recommend the Moxon to build, only took me a week and was great fun and easy to build.