MFJ Moxon

[Shadetree Mechanic]

I like the idea of building the Moxon. An idea popped into my head: would it be possible to stack a pair of Moxon? Why build one when you can build two just as easy?

 

[Alan Blackmon]

I was able to successfully tune my Moxon on some saw horses while on the ground. I was able to get it to very low SWR I was happy with. When I got it up there was very little change that I can remember. What did happen was the bandwidth was wider when up in operating position. It is pretty well tuned into 10/11/and 12 meter bands. It may not do all of the 10 and 12 meter. I don't know frequencies of them all that well but it did get to some of the band I will say. My brother who is a ameture operator said he would be happy using with his 10 meter mobile he had in his truck.

 

[tba02]

KC9Q. Very helpful . I put my Moxon up today. Used the measurements for 10 meters. It seems to have the lowest set at 29.2 MHz. I’m going to adjust it out tomorrow as far as I can safely.Thanks

Here's what I have been using @ 20 feet . It covers 27.385 and targets 28.300
All numbers in inches
A =156
B = 21
C = 6.75
D = 29.75
E = 57.5

 

[donny dobbs]

Here's what I have been using @ 20 feet . It covers 27.385 and targets 28.300
All numbers in inches
A =156
B = 21
C = 6.75
D = 29.75
E = 57.5

I used your measurements. Strangely the swr is 2 to 4 on 11 meters, lower on 10 meters. I’m going to try tuning with wires . Another problem I can’t help is the power lines are 23 feet away and seem to lower receive. I’m gonna have to raise it from 20’ to be able to use it pointing south.

 

[tba02]

Donny, try adding a 1:1 balun (though you can still just tune using different measurements). I use a cheap mfj-915 isolator which seems to tame the SWR numbers.

 

[Shadetree Mechanic]

Donny, try adding a 1:1 balun (though you can still just tune using different measurements). I use a cheap mfj-915 isolator which seems to tame the SWR numbers.

I just put a 915 in my little shack and I thought my SWR meter broke. I swapped the 915 in and out a few times I could not believe it helped that much.

 

[donny dobbs]

Let me straighten this out.

1. when I built Moxon antennas I used the MoxGen application, a center frequency of 27.385, and I had to change the center freq from 27.385 to something higher to get an antenna that operated on center where i wanted it. MoxGen made both wire and tubing antennas lower down on the band than I wished.

2. when I posted the above two diagrams it was from an online calculator. I used a center frequency of 27.2 for the 11 meters dimensions and 28.4 for the 10 meters antenna. I know nothing of its accuracy.

3. I used 1/2" tubing for the metal antennas, and #14 wire for the wire antennas. I left the insulation on the wire antennas.

I believe the tubing antenna is more durable.

Here is the exact measurements of my Moxon I have up now. according to MFJ-259 it has a center frequency of 27.3.

View attachment 17055

 

[donny dobbs]

The Moxon has been up a few days. 6’ above roof 20’ high. I am 18’ from power lines. When pointing at power lines receive goes away almost completely. Away and I get tons of noise. NB , ANL , and ferrite choke trying to hide this problem. I can probably go up 10 to 12 more feet . I’d then be 6’ above the power lines .
My question is should I try an antenna tuner? On 11 meters 27300 my swr is 2 and power reads 20w. My radio puts out 12w. 2) should I swap antennas and put the Moxon on the mast that is 10’ farther from the power lines and maybe go above 30’. My 5/8 ground plane then would go just above the trypod since the length could hit them in a catastrophy.
My idea originally was a good horizontal for DX on 10,11 meters. Thanks again

 

[Marconi]

Definitely needs a choke, you can get some strange results if you have a CMC problem
Guess that is why some report that the position of the coax is so important.
Finally it's a 2 el beam forward gain is about the same as any other 2 el. what makes it special is the coupling of the bent elements providing that bandwidth , match and F to B. I think the future of yagi antennas will be with critical coupled (bent) elements.
This is some of my observations based on making dozens of Yagi, quads, moxons, skyppers and quagis .
Would love to hear your real world experiences and results.

This is an old thread, and unfortunately, vkrules has not been on the forum in several years, but here is what happens, just like he told us, when we add a feed line to the model, then we see the Common Mode Currents (CMC) pop-up and distorts the pattern and mucks-up the match badly.

 

[711]

One thing I forgot to mention was the significance of the position the feed line needs to enter the driven element perpendicular to the element . Any other angle , I found affects the VSWR

 

[Marconi]

One thing I forgot to mention was the significance of the position the feed line needs to enter the driven element perpendicular to the element . Any other angle , I found affects the VSWR

711 in general I would agree, but do you think this installation with the choke hanging down should make a difference like you describe?

 

[HomerBB]

With that installation the SWR was very low. Good directionally although somewhat broad and really good F/B.

 

[711]

I found it didn’t matter too much on the tubing version for some odd reason compared to the wire version. Pics from my last QTH

 

[Marconi]

Form this thread you said:

What does Exnec say about a couple of Moxon Calculators?

My amp builder saw my wire Moxon I had up in the back yard at a stateside house I had and he put one up on my measurements and made it rotatable between horizontal and vertical, with a little higher reflect in the vertical plane , I suspect due to the tower , he worked locals very well also.

I asked for pictures hoping to see how your buddy got the Moxon from horizontal to vertical, like you described.

Since you don't have a picture, maybe you can tell me how he did that trick.

 

[711]

He told me he used a Yaesu elevation azimuth rotator.