What is a good drill bit for installing an NMO mount?

[prcguy]

Uni-Bits / Step Bits are OK until they aren't.
3/4" Hole Saws MAY make the hole too large.
Theres a right tool for every job.

An NMO mount is fairly forgiving on hole size and up to about 1/16" over should not be a problem if there is no burr. A hole saw should make an accurate hole unless the pilot drill hole enlarges allowing the saw to wander. I haven't seen that on vehicle sheet metal enough to worry about since the cutting process goes so fast.

 

[JoshuaHufford]

Stopped by my radio shop today, just to drill the 3 holes and put in the NMO mounts with no routing of the coax and no crimping on connectors would cost me $195, and they are booked until mid August.
I know it is expensive, but I'm just going to get the good bit and do it myself. I can justify it as a business expense, and it isn't going to break me. If I ever need it again, then I have it. I've spent a good portion of my life making due with the wrong tools or cheap tools, I'm past that point in life.

 

[JoshuaHufford]

Forgot to mention, that was the quote for just the labor, that didn't include the mounts.

 

[JoshuaHufford]

So I finally got around to installing 2 of my 3 mounts yesterday, I've been super busy and it has been really hot this summer, I just haven't had the motivation or the time to do it. I did run out of time to do the third but I can do it another day. Everything went great, the drill bit works wonderfully. I put the mount for the cell booster all the way at the back and middle to try and get as much separation between the outside and inside antennas, I put the booster itself on one of the cross members in the cargo area, the coax length from the antenna to the booster is maybe 4ft. at most, shouldn't have much signal loss.

I mounted my CDM radio on the back of my center console storage unit, eventually I'm going to put a remote head up on the overhead light console so it will be easier to see and access, then mount the radio back in the cargo area, but I need to find a remote kit for it first. I was really debating on what kind of antenna to get for this, since I take this van through an automatic car was a lot I decided to try a low profile antenna so I wouldn't have to take it off each time, I got it on Ebay for about $30 so I figured it was worth a shot. This is the specific antenna only in white. I know it will still be a performance compromise, but still way better than nothing.

TRABT1500 | TE Connectivity Antenex VHF Omni Antenna 150-168 Mhz - 3/4 Inch NMO. Ground Plane Required. Soup Can Style Phantom. Black

Note: Field tuning is REQUIRED for this antenna, see tuning guide below: This unit is a Black 'Phantom' style / Stealth VHF Omni-directional antenna with standard 3/4 inch NMO-mobile mount operating at 150-168 Mhz range. This antenna is a 'Soup Can' style and offers a powerful punch with up to 3...

www.arcantenna.com

My main interest is Railroad, I'll see how well it works. I used my NanoVNA to tune it, I was really surprised how narrow of bandwidth it has, I was able to get an SWR or about 1.6 at the edges of the railband, about about 1.3 at the center. Most of my Public Service stuff around here uses repeaters so you can pick them up with just about anything.

This should make the work day more productive and enjoyable.

 

[JoshuaHufford]

Since you can only do 10 pictures in a post, here is another shot of the CDM, where the inside antenna for the cell booster is mounted, and a phone signal screen shot with the booster on and off.

 

[mmckenna]

but I need to find a remote kit for it first.

They're still out there if you search.
You don't need the 'official' Motorola extension cable if you don't find one. A standard RJ-45 4 pair patch cord will work just fine. The outer two conductors on the 5 pair cable Motorola sells only gets used if you have the telephone style handset.

I was really debating on what kind of antenna to get for this, since I take this van through an automatic car was a lot I decided to try a low profile antenna so I wouldn't have to take it off each time, I got it on Ebay for about $30 so I figured it was worth a shot. This is the specific antenna only in white. I know it will still be a performance compromise, but still way better than nothing.

That 2MHz bandwidth is the problem for most. Makes them a very specialized/niche product. But if it works for your railroad listening, then it's good to go.

This should make the work day more productive and enjoyable.

Nice job. The permanent mount NMO's make a big difference in looks. It takes the install from hobby into the professional world.

 

[tvengr]

I mounted many antennas on our news vehicles. I used the 3/4" round Greenlee chassis punch available in our shop. The chassis punches make a very clean hole with no burrs. You will want to sand down to bare metal around the outside of the hole on the inside of the roof to ensure you have a good ground connection from the antenna mount to the vehicle. You need to be careful and inspect the underside of the roof to check for braces and electrical wiring. I often dropped the dome light in news cars to gain access to the inside of the roof and removed the door post covers to route the cable down under the dash for scanners or removed roof liner covers and post covers in the rear for 2-way radio T/R units mounted in the trunk. Unfortunately, the car manufacturers must have gotten together to make it more difficult to install radios doing things like gluing the liner to the roof and eliminating terminals in fuse boxes. I really enjoyed putting holes in vehicles not my own.

 

[mmckenna]

Chassis punches are a nice option if you can access both side of the roof. They do make a nice clean hole and very little chance of making a mistake. I've got one in the drawer right next to the NMO saw. I've used it a few times to make custom brackets where it was easier than trying to get the bracket in a vise without damaging it. A great resource to have.

But I've never needed to sand the underside of the roof. All the NMO mounts I've ever installed had teeth on the inside part that bit into the metal just fine. Won't hurt to do it if you can get to the underside, but if installed properly it's not a requirement. I honestly cannot remember the last time I dropped a headliner to do an install.

 

[N4VX]

I've drilled literally thousands of NMO holes in my career and used several brands of official NMO specific hole saws. I recently switched to these and probably won't go back. https://www.amazon.com/Bosch-HTW34-Thin-wall-Hole-Saw/dp/B007VHHLZC/ They work equally well in steel and aluminum body panels. There is a ridge at the back of the hole saw to prevent over-penetration to punch thru your headliner. Several different brands are available but these hold up really well.

Couple of tips:

• Go slow on your drill speed, almost as slow as it will go.
• Use lubrication even WD-40 if that is all you have, it's better than nothing.
• Deburr your hole with a file or deburring tool, it won't cut your coax insulation on pulling it thru.
• ALWAYS drop your headliner first to check for wires, structural crossmembers, animals, ducts, etc.
• Route your coax on the outside of side curtain airbags, you never want it between the airbag and you to prevent proper deployment.

 

[prcguy]

So I finally got around to installing 2 of my 3 mounts yesterday, I've been super busy and it has been really hot this summer, I just haven't had the motivation or the time to do it. I did run out of time to do the third but I can do it another day. Everything went great, the drill bit works wonderfully. I put the mount for the cell booster all the way at the back and middle to try and get as much separation between the outside and inside antennas, I put the booster itself on one of the cross members in the cargo area, the coax length from the antenna to the booster is maybe 4ft. at most, shouldn't have much signal loss.

I mounted my CDM radio on the back of my center console storage unit, eventually I'm going to put a remote head up on the overhead light console so it will be easier to see and access, then mount the radio back in the cargo area, but I need to find a remote kit for it first. I was really debating on what kind of antenna to get for this, since I take this van through an automatic car was a lot I decided to try a low profile antenna so I wouldn't have to take it off each time, I got it on Ebay for about $30 so I figured it was worth a shot. This is the specific antenna only in white. I know it will still be a performance compromise, but still way better than nothing.

TRABT1500 | TE Connectivity Antenex VHF Omni Antenna 150-168 Mhz - 3/4 Inch NMO. Ground Plane Required. Soup Can Style Phantom. Black

Note: Field tuning is REQUIRED for this antenna, see tuning guide below: This unit is a Black 'Phantom' style / Stealth VHF Omni-directional antenna with standard 3/4 inch NMO-mobile mount operating at 150-168 Mhz range. This antenna is a 'Soup Can' style and offers a powerful punch with up to 3...

www.arcantenna.com

My main interest is Railroad, I'll see how well it works. I used my NanoVNA to tune it, I was really surprised how narrow of bandwidth it has, I was able to get an SWR or about 1.6 at the edges of the railband, about about 1.3 at the center. Most of my Public Service stuff around here uses repeaters so you can pick them up with just about anything.

This should make the work day more productive and enjoyable.

The self adhesive cable ties will come loose sooner than later due to the heat from the roof. Just be aware of that.