OH2BEN's 10 MHz Yagi Style Moxon
First of all, this has been a very long project for me. All started at the end of year 2000, when I tried to find a more effective antenna for 7 and 10 Mhz. Browsing internet I found L.B Cebik's superb antenna pages, and it really gave some really new ideas. After awhile, I sent email to L.B.Cebik and asked any possibilities to build a 30 and 40 meter Moxon on the same boom. After a couple of months L.B. Cebik published an article: 40 + 30 = 50 (Not 70) to answer me and some others. At that time this antenna construction seemed to be too big for an apartment building QTH. During these years fiberglass fishing poles prices have decreased and created new possibilities to construct big beam antennas cost efficiently. Real triggers to start my project were new QTH in the country side and possibilities to raise more antennas and S51EQ's & HB0LL's photos and YU1QT's instructions of constructing of 7 MHz Moxon beam.
Here is some data of my 10 MHz yagi style Moxon beam.
Dimensions
I start with Moxgen calculator, resonance frequency 10.120 Mhz, using 2 mm wire. MoxGen gives values:
A 10,81 m
B 1,66 m
C 0,26 m
D 2,00 m
E 3,93 m
I built the antenna with these measurements and tested it at 5 m high. Result: Moxon's resonance was at 9,860 Mhz, 260 kHz too low. After reading Moxon Antenna Projects pages and Tower Talk discussion board, I found that dimensions can be corrected using percentage difference formula or calculating dimensions again with MoxGen, but this time +260 kHz higher, in my case 10.380 kHz. I corrected antenna with new values:
A 10,53 m
B 1,61 m
C 0,25 m
D 1,95 m
E 3,82 m
This time the dimensions hits the bull's eye. SWR is between 10.100 - 10.150 1.1 and no more tuning or balun is needed. SM5JAB study of "What matters" when building Moxons gave a nice idea how to check F/B-ratio using alligator clips and hairpin match. In my case, calculated values performed best. It was checked out on the band listening JA-stations and FIFA DL-stations pileups.
Driven element
Element hose clamps.
Feedbox.
Element insulator-spacers.
I bought 6m fishing poles from local low cost market Hong Kong, which sells everything from tools to sports. There was the best pole selection with reasonable prices. Just for the record fishing pole prices:
4m 4,95 euros
5m 5,95 euros
6m 7,95 euros
7m 8,95 euros
8m 12,95 euros
At this point here in Finland we have very long days and short nights, so I'm just waiting for better conditions in the winter season and good gray line and long path openings. But here are some first brief comments. 10 Mhz Moxon works very well and like a BIG gun. Better than I first expected. On the band F/B is very good and acts quite similar with my LPDA on the other bands. With amplifier I can work everything what I can hear and get thru big pile ups quite easily, f.ex 4O3T's first day huge pileups. Band seems to be more silent now.
S/N ratio with Moxon is much better than compared to verticals or half square. On the band there are quite often very powerful stations & QRN noises. With Moxon's directivity and better F/B it is now easier to read and dig out weak signals.
Some comments from the band: For couple of days 9J2VB has been worked like a beacon on 10 MHz. I have to turn Moxon to right direction to get it audible. The antenna's pattern acts similarly as the model shows. Moxon is often 2-3 S units better then verticals. With verticals VY0/KD6WW signal was 439 and with Moxon 579. So Moxon works like a beam should be.. This antenna is here to stay !
With these good results, I started to figure out how I can put 7 MHz Moxon up. But this project will be an other story, because I have to clear place for a new tower etc. But I have already 10 meter crank p tower and 4 pieces 7 meters fishing poles waiting for this project :o) Maybe next summer...
I just made measurements with MFJ-259B from the ham shack:
MHz SWR R X
10.000 1.8 37 23
10.050 1.5 37 13
10.100 1.3 40 8
10.150 1.1 45 6
10.200 1.1 46 7
10.250 1.2 46 8
10.300 1.2 43 8
10.350 1.2 41 7
10.400 1.3 40 7
73's & GD DX de Tom/ OH2BEN
Tom can be reached at the following email addresses:
oh2ben @ sral.fi tomi.laakkonen @ luukku.com
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