First NMO Install--Advice Please!

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BUCKSHOT_106

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Well I'm going to attempt my first nmo antenna installation on the roof of my '98 F-150 tomorrow evening. I want it to be centered toward the back side of the roof. I have my 3/4'' hole saw and drill and am fairly confindent in my work. I have helped with installs of this nature before but never tackled myself. I'll be running RG-58 to my new Icom F121 VHF mobile.

Thanks,
BUCKSHOT_106
 

W6KRU

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I have friend who is a fabricator of race trucks and I help him with radios and antennas. I learned a trick from him in drilling a hole. He has a bit that slopes from small to larger diameters. I don't remember what he calls it exactly. Once we get close to 3/4" we slow down and do a little at a time. When we stop, we try to push the mount through the hole. If it doesn't fit we take out a little more. That is a little anal but it results in the best mount you can get. I like to take a little sandpaper to the bottom of the roof around the hole so the mount gets a good connection.

If you want to put the antenna in the back of the roof it might be pretty easy to do it right above the dome light but your reception will be slightly distorted. The best spot is the center of the roof, but then you have to drop the headliner a bit. I know a lot of guys that put them in the back of the roof for race radios and they work OK. Your call.
 

W6KRU

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For your guy's info: they make special hole saws designed specifically for installing NMO mounts.

Yeah I know. When I worked in a shop I used a greenlee punch. You can make a hole a lot of ways.

Yeah. Unibit that's it. My buddy already had one of these and didn't see any reason to do it any other way. It is probably the most anal way to do it, the fit is perfect. :roll:
 

WayneH

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My vote goes to the Antenex. It's what I own and swear by. No worries about tapping the inside of the head liner.

If you aren't drilling holes on a regular basis and not doing it on someone else's vehicle then I suppose a regular hole saw is fine. Why worry about it though?
 

AK9R

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When I installed the NMO mounts in my Ford Expedition, I used a Unibit. It worked pretty well, in my opinion.

Hardware store hole saws are really intended for wood and seem to do a crappy job on sheet metal. The hole saws that Antenex, Maxrad, and others sell specifically for NMO mounts have fine-tooth blades and the blades are just long enough to cut through the metal which I think adds some stiffness to the blade.
 

BillyFred

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The hole saw will work fine. Only big issue is the fact it's long and very easy to tear up a headliner. The unibits aren't much shorter. The bits like the antennex have a stop and are very shallow.

You may already know but the NMO mounts from the outside. Barely start the outer nut and feed coax through the hole and slide the little feet under. A couple of important notes, make sure the O ring is in place and use a good amount of silicone grease (NOT sealant). No grease on the center contact but on all the threads and on the O ring. This will allow the ring to slide on the roof and not bunch up giving you a long lasting water seal.

It's not rocket science but requires you to be careful in what you're doing. Also remember to pay attention to your coax route. Stay away from any airbags or sensors.
 
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If you need it fast the unibit, step bit, is a good tool but they aren't cheap if you only need it once. I don't know what they are at Harbour Freight but the big blue box wants 40 bucks for theirs. The antenex is 20 bucks and you don't have to worry about it punching through. I would not use a regular 3/4 bit as they can shred the thin metal as they break through at the end if you let it get out of control. You may need to use a small file or emory board to clean up the underside of the hole. The first hole you punch through your OWN car can be a bit unnerving, just go slow and keep a good firm grip on the drill and everything will be fine.

The antenex is also pretty good for drilling through the firewall so that you don't accidentally hit something on the other side.
 
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BUCKSHOT_106

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Ok guys I'm almost convinced on the unibit method. I'm going to do it either this evening (if the weather permits) or tomorrow. I'm let you know how it goes and post some pics it it turns out looking OK. :lol:
 

AK9R

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Take it slow with steady pressure and keep your drill as perpindicular to the surface as possible. If you don't, the flute on the Unibit will grab and tear a burr in the hole. I put a dab of white paint in the flute on the 3/4" step so I could see when I was getting close to the right step (you can't read the numbers while the drill is spinning). Once you get to the 3/4" step, use light pressure on the next step to knock off the burr around the hole on both sides of the metal if you can.

One other thing I did was to dab just a little bit of Rustoleum primer on the bare metal edge of the hole. Your NMO mount should have teeth on the under side that will dig into the surface under the mount to make a ground connection.
 

deltabravoks

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Hole Drilling

I assume you removed the cab light to get to the place where your antenna wiring will meet the hole.

My only advise would be to slip some heavy cardboard or sheet metal scrap through the cab light hole between the exterior shell (where the hole is being drilled) and the headliner. I've seen drills pierce the outer shell and then go right through the headliner. Having another layer there gives you something to bounce on once the outer shell is pierced.

Regards
 

motorola_otaku

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Your NMO mount should have teeth on the under side that will dig into the surface under the mount to make a ground connection.
I still scrape away the paint underneath the roof/trunk lid/whatever to make sure the mount gets a good ground bite. It's not so much an issue on UHF and up, but you can notice decreased performance on VHF and especially lowband and CB if the ground at the mount is poor.

I'm also a big fan of the 3/8-3/4'' dual-size hole mounts. When used with a 3/8'' hole they grip a much larger area of the mounting surface and you can use a regular metal bit to make the holes.. provided you're careful and easy on the drill. ;) For reference, their Tessco part numbers are 39173 and 489628.
 

IdaScan

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I'm not sure if this was brought up already...

From the top, when drilling, apply masking tape to the hole and the area around it...

Keeps the scratches from the shards of hot sharp metal from the hole popping up and scratching your paint... Also tends to save you if you do make a mistake and slip...

Always drill a pilot hole first (uber small) to verify clearance on the other side... Makes drilling with a hole saw a bit easier :)

Use a deburring tool on the edges of the hole to ensure a good mechanical connection that isn't going to cut your fingers off when you try routing the mount thru the hole.

Typically we do sratch away the undersurface part of the sheet metal for a good binding contact, however, we run primer on the edges of the sheet metal of the hole to prevent rust if the seal on the NMO fails. On industrial applications (i.e. trucks going to Canada), we also spray everything down with primer on the underside to keep rust from occurring where the paint was scraped off for the under contact. This is AFTER tightening up the NMO mount.

Bravo for taking the jump and getting away from mag mounts!
 

AK9R

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From the top, when drilling, apply masking tape to the hole and the area around it.
Good point. When I put in my my NMO mounts (yes, plural), I put blue painters tape in the general locations of the holes and then spent an hour or so with a tape measure and a fine-tip Sharpie to lay out the holes.

Once I had the locations determined, a quick hammer tap on a center punch to mark the spots. Don't go crazy with the hammer otherwise you may dimple the roof. Don't know about the OP's F-150, but I was surprised at how thick the sheet metal was on the roof of my Expedition.

Use a deburring tool on the edges of the hole to ensure a good mechanical connection that isn't going to cut your fingers off when you try routing the mount thru the hole.
I took the easy way out and carefully knocked off the burrs with the next step of the Unibit.
 
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