Moxon-Principles | Dualband-Moxon 10+6 m | Moxons 10-15 m | Wire-Moxon 17 + 20 m | 2-m-Moxon |
The Moxon-Beam By DK7ZB |
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The Moxon-Beam was introduced by L. Moxon (G6XN) in his book "HF Antennas for all Locations" (RSGB- Publications, Great Britain 1993). This beam is a 2-Element-Yagi with radiator and reflector and reduced size to about 75% of a normal beam. The 2-Element-Yagi with reflector has normally a 0,2-lambda-boom and an impedance of 50 W. The Moxon-beam has a 0,18-lambda-boom and still 50 Ohm. This is a good impedance for wire- beams.The ends of the two elements are bended backward (radiator) or forward (reflector) and act as a capacitive load. That is much better than inductive loading with coils. So we have greater bandwidth and lower losses.Through the reduced size we get a 0,5-0,7 dB lower gain than with a fullsize beam. The construction of the beam is seen in the picture left. |
This type of a 2-Element-Yagi has an unbelievable
F/B-ratio on the design frequency of >= 30 dB. That is higher than
with any other 2-Element-Beam.
The gain is higher on the beginning of the band and lower at the end. The bandwidth for a SWR < 1,5 is great enough for the range of 28,0-28,7 and 21,0-21,45 MHz if the beam is built up with aluminium tubes. Wire-beams of the Moxon-type have a smaller bandwidth. The design frequency should be for a frequency 1/3 from the beginning of the band, because the SWR raises more below the design frequency. For example look for the SWR of a tube-Moxon for the 15-m-band: |
Designing a Moxon- Beam is very easy with a useful little
program by D. Maguire, AC6LA with the name "Moxgen".
This freeware can be downloaded at: Moxgen generates an output file for "EZNEC" for modifications (e.g tapering) and shows you the dimensions for building a wire-Moxon. Left a screenhot of Moxgen. |
Building a Wire-Moxon for the Shortwave-Bands
The Wire-Moxon for the 17-m-Band Lightweight construction with fishing rods. Do not use the thin end parts of the rods! |
How to build a supporting structure for a shortwave wire-Moxon. Use a middle spider of aluminium tubing and spreaders of fishing rods. For the lengths of the different parts see the table below. |
The lengths for the Wire-Moxon, only for non-insulated 1-mm-wires!
S is the complete length of the radiator wire, R for the reflector, F for the spreader.
Band |
S |
R |
A |
B |
D
|
E |
F |
6m |
282,6cm |
298cm |
218cm |
32,3cm |
40cm |
79,5cm |
153cm |
10m |
504cm |
529cm |
386cm |
59cm |
71,5cm |
140cm |
205cm |
12m |
572cm |
600cm |
440cm |
66cm |
80cm |
160cm |
234cm |
15m |
674cm |
706cm |
516cm |
79cm |
95cm |
187cm |
275cm |
17m |
788cm |
826cm |
606cm |
91cm |
110cm |
220cm |
321cm |
20m |
1011cm |
1057cm |
772cm |
119,5 |
142,5cm |
280cm |
411cm |
30m |
1410cm |
1476cm |
1084cm |
163cm |
196cm |
392cm |
576cm |
The insulator for the ends of the wire. Do not bend circles, they act like end capacitors and cause a frequency shift! |