Wednesday, November 16, 2011

Building a 10M Moxon Antenna

Since the 10 meter band is now well and truly open I’d love to have a yagi for a bit of directional activity, but unfortunately I don’t think I will get the official stamp of approval so I’ve 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 aliminium 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).

So far the rectangle has been built and I have used an old TV antenna as the boom and pinched the plastic feeder complete with circuit board, but on testing I think I have over complicated the build so have 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 show the SWR to be very high at 28.100 but an acceptable 1.3 at approx 26.500 so some trimming will be required.

Having done further checks on the thickness of the tubing I realised I had over compensated. The tubing is a mixture of 8, 10 and 12mm with the majority being at 10mm. so I have recalculated at 10mm and of course my original dimensions are slightly out, hence the high SWR. So last night I dismantled the rectangle and will now begin to re-trim to the correct lengths for 10mm, lets see if that makes difference, I’m told that the space between the reflector and driven elements are very important so I must make sure I get that absolutely correct; Any advice would be mucho appreciated……..more updates and pictures later!

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