Ground plane for NMO Mag Mount

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N5JMC

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I have an NMO Mag mount that I'm using in the attic for now on 2m/440 and an just using a baking sheet. I'm going by Lowe's and wondering if there's something better I can use.


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mmckenna

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I have an NMO Mag mount that I'm using in the attic for now on 2m/440 and an just using a baking sheet. I'm going by Lowe's and wondering if there's something better I can use.


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On the lowest frequency, the ground plane will need to be the largest. So, 144MHz will need about 19.5" in each direction under the antenna. That ideally would be a 39" wide circle with the antenna mounted in the middle. Going out and buying a piece of sheet metal that large would certainly be an option, but it's not necessary.

If you go to where they have their roofing supplies, they should have a pretty good selection of various flashing materials. You should be able to buy a roll of thin sheet metal a couple of inches wide. Just make a big "X" with that, each piece about 40 inches long. Put your NMO mount in the center.
The thinner the material is, the easier it is to cut. If you get something thin enough, you can cut it with a hefty pair of scissors. If not, get your self some cheap sheet metal sheers.

And, the material really doesn't matter too much, other than using ferrous metal will allow the magnet to stick. But, in reality, there shouldn't be any movement or wind in your attic, so all you need is a conductive metal, aluminum, brass, copper, etc. to do the trick.
If you wanted to do a trial, you could even lay down some aluminum foil and put the antenna on that.

You could also go really cheap and just use aluminum foil you probably already have in your kitchen. Just tack/staple/glue it down on a wood support. Could be some 2x4's, plywood, masonite heavy cardboard, etc. anything to give it a nice flat platform.

You could even use scrap wire, chicken wire, wire mesh, aluminum window screen, etc....
 

N5JMC

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On the lowest frequency, the ground plane will need to be the largest. So, 144MHz will need about 19.5" in each direction under the antenna. That ideally would be a 39" wide circle with the antenna mounted in the middle. Going out and buying a piece of sheet metal that large would certainly be an option, but it's not necessary.



If you go to where they have their roofing supplies, they should have a pretty good selection of various flashing materials. You should be able to buy a roll of thin sheet metal a couple of inches wide. Just make a big "X" with that, each piece about 40 inches long. Put your NMO mount in the center.

The thinner the material is, the easier it is to cut. If you get something thin enough, you can cut it with a hefty pair of scissors. If not, get your self some cheap sheet metal sheers.



And, the material really doesn't matter too much, other than using ferrous metal will allow the magnet to stick. But, in reality, there shouldn't be any movement or wind in your attic, so all you need is a conductive metal, aluminum, brass, copper, etc. to do the trick.

If you wanted to do a trial, you could even lay down some aluminum foil and put the antenna on that.



You could also go really cheap and just use aluminum foil you probably already have in your kitchen. Just tack/staple/glue it down on a wood support. Could be some 2x4's, plywood, masonite heavy cardboard, etc. anything to give it a nice flat platform.



You could even use scrap wire, chicken wire, wire mesh, aluminum window screen, etc....


Thank you for this. Could I lay the sheet metal you mentioned in an X on wood for support or is it bad to have something under it? Thinking maybe a 2x whatever the rolls of sheet metal are or even plywood. But if that's not a good idea please let me know. I know you mentioned this for the aluminum foil but wasn't sure if it made a difference for the sheet metal. Or what would you recommend to put it on?


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DJ11DLN

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no problem on support under the metal. Not sure you mag mount would stick to aluminum foil.
Being it's to be in an attic, it should just sit on the aluminum. Unless he has critters in his attic, which would be a subject for another forum. But the OP could just put a small piece of ferrous metal under the middle of the foil X if he was worried about movement. The lid from a metal can (soup, vegetable, whatever) comes to mind. Tack it down where he wants his antenna, apply & tack the foil over it, stick the antenna down, done and done.:cool:
 

mmckenna

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Thank you for this. Could I lay the sheet metal you mentioned in an X on wood for support or is it bad to have something under it? Thinking maybe a 2x whatever the rolls of sheet metal are or even plywood. But if that's not a good idea please let me know. I know you mentioned this for the aluminum foil but wasn't sure if it made a difference for the sheet metal. Or what would you recommend to put it on?
Doesn't matter what's under it. Just something rigid enough to support it all.
Likely your attic access is going to be the limiting factor. If I was doing this, I'd probably make an "X" out of something like 1x2, cover it with foil, sheet metal, screen, etc. and just place it up in the attic.

This should work just fine, UNLESS your roofing material has any metallic components. Hiding your antenna under a metal roof isn't really going to be beneficial.
 

mmckenna

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Not sure you mag mount would stick to aluminum foil.
Since aluminum doesn't have any ferrous metal in it, the magnet isn't going to stick, but that's OK. In an attic, all it's got to do is sit on top of the aluminum to achieve the capacitive coupling it needs to utilize the ground plane. True, the mount will be relying on gravity to hold it in place, but that won't be a problem. If it is a concern, like stated, use a tin can lid or something similar and put it under the foil.
 

N5JMC

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Was only asking as I have it on top of boxes right now to get it higher. No critters just asked to get support to have it higher. If support would this X or even big square of sheet metal work on top of plywood? Asking cause I don't see the difference in laying it on the plywood which is the floor.

If I buy those rolls of sheet metal and just buy a sheet of plywood big enough for already 19.5" in all directions I could just cover that in the rolls of sheet metal right? But would I just overlap them and every 6 inches screw into both sheets and the plywood? Or what's the best way to connect them?

If there's something around 25"-30" square or round that would do it I'm up for buying that. Just need to support it with plywood if flimsy as I'll have it on top of boxes or may even tack some 2x4s on top existing framing to set this on to get it higher.

My ultimate plan is to get a diamond x50 and hang up upside down by throwing rope over one of the top beam sports that's a few feet from peak of attic. When standing in attic the peak is 20-25 feet high. Then I'll tie the rope to the bottom of x50, hook lmr400 to it and pull out up with the rope and tie it so it stays up.

Until then I have to get by with this NMO Mag mount which is doing pretty good. I'm getting repeaters that are 40 miles "as the crow flies" to my northeast easily, but having issues hitting them 28.51 miles "as the crow flies" to my southwest. However I can hit some that are 35 miles to my west. When going south there's a major road for the town just south of us that some say is a hill but it's not, I think it's due to a lot of potentially RF that's blocking everyone from getting past is good. I can get past it but just can't go as far in that direction. So that's why I plan to get the x50 and get a little higher. It will be about 15-20 feet higher than the NMO Mag mount is right now in the attic.


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DJ11DLN

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Was only around as I have it on top of boxes right now to get it higher. No critters just asked to get support to have it higher. If support would this X or even big square of sheet metal work on top of plywood? Asking cause I don't see the difference in laying it on the plywood which is the floor.

If I buy those rolls of sheet metal and just buy a sheet of plywood big enough for already 19.5" in all directions I could just cover that in the rolls of sheet metal right? But would I just overlap them and every 6 inches screw into both sheets and the plywood? Or what's the best way to connect them?

If there's something around 25"-30" square or round that would do it I'm up for buying that. Just need to support it with plywood if flimsy as I'll have it on top of boxes or may even tack some 2x4s on top existing framing to set this on to get it higher.
Any of this will work just fine. Generally, the bigger the better as ground planes go...the 19.5" figure is just a minimum. If you can get a whole sheet of plywood covered with mesh, foil, sheet metal, or whatever, it will work great.

My ultimate plan is to get a diamond x50 and hang up upside down by throwing rope over one of the top beam sports that's a few feet from peak of attic. When standing in attic the peak is 20-25 feet high. Then I'll tie the rope to the bottom of x50, hook lmr400 to it and pull out up with the rope and tie it so it stays up.

Until then I have to get by with this NMO Mag mount which is doing pretty good. I'm getting repeaters that are 40 miles "as the crow flies" to my northeast easily, but having issues hitting them 28.51 miles "as the crow flies" to my southwest. However I can hit some that are 35 miles to my west. When going south there's a major road for the town just south of us that some say is a hill but it's not, I think it's due to a lot of potentially RF that's blocking everyone from getting past is good. I can get past it but just can't go as far in that direction. So that's why I plan to get the x50 and get a little higher. It will be about 15-20 feet higher than the NMO Mag mount is right now in the attic.


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Hanging that antenna up in the manner you describe would not IMHO be a good idea. If you can come up with some kind of tripod mount to hold it up there properly oriented, I believe that would result in much better performance for you. If you do experiment with hanging it by the base, at least run the coax away from it at a right angle i.e. along the roofpeak for a few feet. Having it hang down that way parallel and close to the radiator can cause SWR and other issues.
 

mmckenna

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Was only around as I have it on top of boxes right now to get it higher. No critters just asked to get support to have it higher. If support would this X or even big square of sheet metal work on top of plywood? Asking cause I don't see the difference in laying it on the plywood which is the floor.
Yes, that will work. Basically you are making a set of radials under the antenna. 3 or more radials will work fine. A single 39" square will work fine. A 39" circle will work.

If I buy those rolls of sheet metal and just buy a sheet of plywood big enough for already 19.5" in all directions I could just cover that in the rolls of sheet metal right? But would I just overlap them and every 6 inches screw into both sheets and the plywood? Or what's the best way to connect them?
Sure, doesn't matter. You just want the antenna mount in the center. Screwing it down to the plywood will work fine. Distance between screws is not critical as long as it all stays where you want it.

If there's something around 25"-30" square or round that would do it I'm up for buying that. Just need to support it with plywood if flimsy as I'll have it on top of boxes or may even tack some 2x4s on top existing framing to set this on to get it higher.
Yep, sometimes it's good to just go to the hardware store and start wandering around and see what you find.
Garbage can lid.
HVAC duct
Aluminum window screen.
Oil drip pan
roof flashing
conduit
copper water pipe
wire
chicken wire
wire mesh
corrugated roofing material
probably 100 different things you'll find by just wandering around.

My ultimate plan is to get a diamond x50 and hang up upside down by throwing rope over one of the top beam sports that's a few feet from peak of attic. When standing in attic the peak is 20-25 feet high. Then I'll tie the rope to the bottom of x50, hook lmr400 to it and pull out up with the rope and tie it so it stays up.
Pay attention to the radiation pattern of the antenna. Some antennas will work fine like this, some will direct power down towards the ground when upside down.
Since the X50 is a lower gain antenna, it'll probably work fine.
Make sure you route the coax well away from the antenna before dropping it down to the floor. You don't want the coax near the antenna vertical element.

I'd recommend rigging up a support to hold the antenna in it's intended orientation. Attaching a conduit/pipe/mast, etc to the rafters to hold it up near the top of the attic space will work, and will allow your coaxial cable run to be shorter.

Until then I have to get by with this NMO Mag mount which is doing pretty good. I'm getting repeaters that are 40 miles "as the crow flies" to my northeast easily, but having issues hitting them 28.51 miles "as the crow flies" to my southwest. However I can hit some that are 35 miles to my west. When going south there's a major road for the town just south of us that some say is a hill but it's not, I think it's due to a lot of potentially RF that's blocking everyone from getting past is good. I can get past it but just can't go as far in that direction. So that's why I plan to get the x50 and get a little higher. It will be about 15-20 feet higher than the NMO Mag mount is right now in the attic.
Topographical shielding will play a big part in your coverage. VHF/UHF is mostly line of sight, so anything that blocks the view will likely block the signal. Increasing antenna gain might help a little bit, but don't expect a drastic difference.
Will will matter is antenna height. Getting the antenna up as high as you can will extend the radio horizon.

40 miles range is pretty good, sounds like what you have is working well.
 

N5JMC

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Found some of this at the house. I know it's not long enough but if I get longer will it work? Basically lay 2 of these on a piece of plywood for support with it forming an X and put antenna in middle? Do I need a screw going into them so they're attached instead of laying on each other at the x?


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mmckenna

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Not sure if there was supposed to be a picture with that post or not, but either way I don't know what you are talking about.

If it something conductive, then yes, it would probably work. Attach in the center with a screw to make a good electrical connection, and it will probably work fine.
 

N5JMC

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I ended up making something like this article. I have 4 rods that are 19.5" out of the box. Will it be better with 6 or even 8? I used 3/8 diameter rods but have the supplies to make anotber with a circle metal plate like in this article using 1/4.

I'll post pics of mine tomorrow.

http://www.n5ese.com/port_gp.html


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mmckenna

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That should work just fine.
The difference between 4, 6, or 8 radials is likely so minimal, you wouldn't notice the difference. Wouldn't hurt to experiment, though.
 
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