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Author Topic: mag mount antennas not on a vehicle  (Read 2438 times)
N9ZRZ
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Posts: 31




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« on: June 14, 2010, 11:49:01 AM »

Hello Elmers,

I am looking to setup a better, but basic portable, antenna system I can use on my deck.  Is it possible to take a mag mount antenna and place it on a wooden deck or table and have good results?  Or does a mag mount need the metal vehicle to operate properly?

73,
N9ZRZ
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KJ4OBR
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Posts: 104




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« Reply #1 on: June 14, 2010, 12:03:00 PM »

Pop the mag mount on a big steel cookie sheet. That will give some ground plane. (might want to by the XYL new ones and take the old ones off her hands)

73
Dave


Hello Elmers,

I am looking to setup a better, but basic portable, antenna system I can use on my deck.  Is it possible to take a mag mount antenna and place it on a wooden deck or table and have good results?  Or does a mag mount need the metal vehicle to operate properly?

73,
N9ZRZ
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AD4U
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Posts: 2173




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« Reply #2 on: June 14, 2010, 12:03:39 PM »

A 1/4 or 5/8 wavelength mag mount antenna MUST have an adequate metal ground plane to operate properly.

Dick  AD4U
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KB1TXK
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Posts: 441


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« Reply #3 on: June 14, 2010, 12:04:23 PM »

+1 for cookie-sheet. Basically anything metal and flat under the antenna will help (or so i've come to understand).
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K5DVW
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Posts: 2193




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« Reply #4 on: June 14, 2010, 12:29:39 PM »

It needs a ground plane under it.  The middle of a 1/2 wave circular piece of metal would be the best, but anything that approaches that is ok if all you care to do is hit the local repeater. How about making a 1/4 wave vertical with 4 radials out of an SO-259 jack and ty-wrapping that and the coax leader to a wooden pole?
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WB6BYU
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Posts: 13337




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« Reply #5 on: June 14, 2010, 12:32:27 PM »

Without the metal ground plane under it, the shield of the coax becomes the rest of the antenna.
Then the pattern of the antenna becomes dependent on what you do with the coax, which may
not be a good thing.

There are some mag-mount antennas that describe themselves as being half-wave resonant, which
means they are less dependent on the ground connection.  A 5/8 wave whip will show more variation
than a 1/4 wave whip.   Any of them likely will be adequate to hit the local repeater and probably
will be better than a rubber duck, but performance will be better with a big enough ground plane
under them (like a trash can lid, cookie sheet, wheel rim, etc.  Doesn't even have to be steel if
the mag mount can stand up by itself.)
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KQ6Q
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Posts: 988




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« Reply #6 on: June 14, 2010, 12:39:10 PM »

If for 2m/440, mag mount on cookie sheet is fine. If for low bands, run  some tuned radials/counterpoise wires to get decent performance. I use some triple magmounts  with HF Mobile whilps on a metal mobilehome roof, AND run a couple of tuned counterpoise wires for each band. works very nicely.

Fred, KQ6q
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KI4SDY
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Posts: 1452




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« Reply #7 on: June 14, 2010, 05:32:42 PM »

I agree with the previous poster. Just get a SO239 connector, some 12 or 14 AWG black insulated solid wire and cut the wire 19 1/2 inches for 2 meters (including the stripped "U" you make to bolt them on the base of the mount for your 4 ground radials and the stripped piece that your solder in the center connector for the radiator) seal the ends of the wire and the top of the connector with black gasket silicone seal or liquid tape. Droop the ground radial down at almost a 45 degree angle off the connector and you will have a much better stealth set up than using a magnetic mount antenna. It is cheap (less than $5.00 and lightweight) so you can get it up pretty high off the balcony with a small diameter PVC pole with no problem. Paint the pole black with $.99 spray paint. If you need to see a picture you can find it on the internet. Check the SWR with a meter when you are done

These simple inexpensive antennas work great and they introduce you to antenna building. Grin     
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CHRISDX
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Posts: 244




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« Reply #8 on: June 14, 2010, 11:00:05 PM »

Without the metal ground plane under it, the shield of the coax becomes the rest of the antenna.


how does my ht rubber duckey differ from my car's 2m mag mount as far as this goes?  is it just that there is no coax?  what about my antron 10m antenna with no ground plane, does the coax do what you said?

i guess i'm asking if mag mounts are designed different than other verticals made to not be on a metal car... and if so, what is the differences.
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W0NFU
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Posts: 46




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« Reply #9 on: June 14, 2010, 11:39:56 PM »

I have a dual (2/440) mobile vertical attached to a mag mount. I placed the mag mount on a sheet of galvanized steel here in the shack. It works great. I can operate both bands and hit all of the repeaters here in Seattle area which I have interest in.

73 - Larry W├śNFU
Lake Forest Park, WA
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WA3SKN
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Posts: 5496




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« Reply #10 on: June 15, 2010, 04:59:00 AM »

Frequency has not been mentioned.
The mag mount relies on capacitive coupling to the ground plane or counterpoise of the antenna, and the surface area of the capacitor plate is limited.
So...
For 2 meters and above, it works well.
For 6 meters it works fair.
For 10 meters and below (HF) it works quite poorly.
So if you have it on your deck, add some sheet metal or aluminum foil under it for a counterpoise.
73s.

-Mike.
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N4NYY
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Posts: 4799




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« Reply #11 on: June 15, 2010, 06:08:50 AM »

What band are us using? If you use 2M, the ground plane will be fairly small. A sheet metal base from Home Depot might work.
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