772 Mhz Moxon antenna project.

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Sep 13, 2005
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375
#1
I was introduced to the Moxon antenna at an amateur radio club recently. Since I had been looking around for an easy to build directional antenna to monitor the local 770 MHz P25 system I decided to run the numbers for 772Mhz and see how big the antenna would be. It turned out to be small enough to sit on my desktop at about 3x7 inches. There are two nice calculators on the web.
Moxon Calculator
W4/VP9KF - Online Moxon calculator
===================
I built the antenna in the attached images using some plastic cardboard material like the political yard signs are made of. A block of wood with a slot cut in it serves as the base. The elements are made from a length of #12 copper wire (2.05 mm diameter) connected to an F type chassis mount coax connector. The wire is held in place with hot glue.

I have no equipment to test this antenna for SWR at this frequency so my performance report is anecdotal to be honest. I can say that it works better than I expected and gives me a better signal according to DSD+ sitting indoors on my desk than does my outdoor folded dipole cut for the same frequency. It is directional but not a sharp beam so aiming isn't critical. I use a TV splitter to send the signal to two SDR dongles.

Anyway so I offer it here for those of you who like to experiment. It is a quick and easy project that exceeded my expectations. If you are looking for an indoor or outdoor homebrew antenna this might be an option. I like it because I recently had lightning damage a computer with SDR dongles connected to an outdoor antenna. This one sits on the desk with a short connection to the dongles.
 

Attachments

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#3
That looks cool. I gots to find some wire and try that out. I might try it on plexiglass...
Plexiglass would be great and would probably hold the F connector a little better. I made a 3/8" loop out of some small gauge wire wrapped around the connector under the nut to solder the #12 wire on the ground side. A 3/8" lug would probably be the "right" way but no big deal.
 

dave3825

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#4
Plexiglass would be great and would probably hold the F connector a little better. I made a 3/8" loop out of some small gauge wire wrapped around the connector under the nut to solder the #12 wire on the ground side. A 3/8" lug would probably be the "right" way but no big deal.
I just found to 14 inch lengths of #12. Now to find an f or bnc in my stash
 
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#6
How should that be oriented? Seen a few pics of them both vertical and horizontal.
Vertical. Most 2-way radio (VHF or higher) is vertically polarized. The antenna is directional. Point the feedpoint toward the tower.
 

dave3825

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#7
I have to say, I am not seeing much in regards to directional. I rotate it 360 and do not see much of an increase or decrease in signal. Both with unitrunkers visual display and the level meter plug in in sdr# But it is picking up much better on a 700 mhz system I was having some trouble with..
 
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#8
I have to say, I am not seeing much in regards to directional. I rotate it 360 and do not see much of an increase or decrease in signal. Both with unitrunkers visual display and the level meter plug in in sdr# But it is picking up much better on a 700 mhz system I was having some trouble with..
It isn't a beam but the non feedline side is a reflector. Glad you got one going!
 

M105

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#11
That is nice but I often wonder how some of these merchants sell anything. No description or dimensions? I tried looking up his callsign on Google to see if I could find out more information without success. Kinda high priced for a pcb board isn't it...
 

boatbod

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#12
That is nice but I often wonder how some of these merchants sell anything. No description or dimensions? I tried looking up his callsign on Google to see if I could find out more information without success. Kinda high priced for a pcb board isn't it...
Especially since he didn't post anything about what frequency these were designed for, other than "UHF" which is a pretty broad brush.
 

dave3825

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#13
I have copper boards but wonder, how do you calculate how wide the strips should be. I mean the one on the pcb looks like maybe 1/4 of an inch. How is that determined?
 

M105

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#14
My guess, and it is just that, would be to use the inside to inside dimensions. Also, from what I have read the gap distance between the driven and reflector elements is very important.
 

dave3825

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#15
My guess, and it is just that, would be to use the inside to inside dimensions. Also, from what I have read the gap distance between the driven and reflector elements is very important.
I mean how wide should whats shown between the arrows be? When you use a copper wire, its something like 12 awg so the calculator knows overall sizes. How can thickness between the arrows be determined?

715MSpA1YAL._SL1200_.jpg
 

nd5y

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#16
It looks like the traces on that board have vias.
That probably means the other side is a mirror image with traces on both sides connected. You would need to take that into account, not just the width of the traces.
You would also have to take into account the dielectric constant of the board material.
 

mrkelso

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#17
I was introduced to the Moxon antenna at an amateur radio club recently. Since I had been looking around for an easy to build directional antenna to monitor the local 770 MHz P25 system I decided to run the numbers for 772Mhz and see how big the antenna would be. It turned out to be small enough to sit on my desktop at about 3x7 inches. There are two nice calculators on the web.
Moxon Calculator
W4/VP9KF - Online Moxon calculator
===================
I built the antenna in the attached images using some plastic cardboard material like the political yard signs are made of. A block of wood with a slot cut in it serves as the base. The elements are made from a length of #12 copper wire (2.05 mm diameter) connected to an F type chassis mount coax connector. The wire is held in place with hot glue.

I have no equipment to test this antenna for SWR at this frequency so my performance report is anecdotal to be honest. I can say that it works better than I expected and gives me a better signal according to DSD+ sitting indoors on my desk than does my outdoor folded dipole cut for the same frequency. It is directional but not a sharp beam so aiming isn't critical. I use a TV splitter to send the signal to two SDR dongles.

Anyway so I offer it here for those of you who like to experiment. It is a quick and easy project that exceeded my expectations. If you are looking for an indoor or outdoor homebrew antenna this might be an option. I like it because I recently had lightning damage a computer with SDR dongles connected to an outdoor antenna. This one sits on the desk with a short connection to the dongles.
I have everything i need in my spare parts box to make this. Now to cut the plexiglass glass to size.
 

M105

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#18
If it were me here's how I would do it: Settle on a dimension for the width of the trace be it 1/4 inch or whatever. Use that width in the calculator as the wire diameter. That should, I would think, spit out the correct center to center distance for the traces. I think the reason the calculators include the wire diameter is so they can figure the inside to inside (non conductive) area properly.
 
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