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Author Topic: How to drill a hole for NMO mount??  (Read 3103 times)
AK2B
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Posts: 94




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« Reply #15 on: April 18, 2005, 12:14:50 PM »

After being in the two-way radio business for the past 20 years,  K5LXP gets my vote for the best way to do this.
If you ever need to remove the mount, Motorola (and others) make a black rubber hole plug for that purpose. There is also available a screw on cover if you want to leave it in place and just cover it up.

Tom , AK2B
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AA4PB
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« Reply #16 on: April 18, 2005, 12:24:17 PM »

I guess ham radio is changing. I thought part of ham radio was about learning to install your own equipment. I've read advise several times on e-ham to "let the professionals do it". From mounting the antenna to installing the radio and routing the wires. Even advise to let the Best Buy stereo guys install your radio.

In all the years I've been installing my own stuff I've never buckled a headliner, bent the roof with a chassis punch or caused a fire with the wiring. I admit that I have had to clean off a few smudges from the headliner before I learned to be more careful. But then I've also had to clean up a few smudges left by the "professional" mechanics at the dealer so I'm not so sure that the fact you pay someone to do it means that you always get a 100% correct job.
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AA4PB
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« Reply #17 on: April 18, 2005, 12:32:18 PM »

The hole saws in the kit I have don't have any collars to prevent them from going on thru the metal. If you are going to use a hole saw I would think this would be a very important feature to have. Otherwise the teeth could grab the insulation and twist and tear it. Probably all vehicles don't have the same insulation, but what I've seen looks like fiberglass insulation that can be easily torn to shreads.
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KE6GLW
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« Reply #18 on: April 18, 2005, 01:25:03 PM »

re: 19" dual-band antenna (N3JBH)

Thanks for the suggestion. I wonder how that would compare to a ~40", 1/2:2x5/8 wave (2m/70cm) for the trunk? I used to run a 1/2 wave off the back rack of a motorcycle and that was pretty nice (Sold the cycle, thinking about installing the antenna on a bicycle next).

A third option is to use a short antenna for the daily commute and swap a better one when necessary. However I kinda like setting up things just once.

- Tim
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OBSERVER11
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Posts: 657




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« Reply #19 on: April 18, 2005, 02:59:15 PM »

I will buck the trend here... I use a stepped drill bit.

I have had CHEAP NMO mounts leak, but if you use a quality product, you will get quality results.

You also should scrape the paint from the INSIDE of the car so you have a better ground.
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KZ1X
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« Reply #20 on: April 18, 2005, 03:08:18 PM »

AA4PB:  "The hole saws in the kit I have don't have any collars to prevent them from going on thru the metal."

There's a special kind of hole saw made especially for installing NMO mounts.  It's almost nothing like any common hole saw, and these are sold only by shops catering to the 2-way industry.  The cutting part of the tool is actually a microtooth bandsaw blade, welded into a circle, with a locator bit in the center, and all of this is in a machined mandrel.  The diameter cannot be changed, and the cut depth (limited by the collar on the special mandrel) is VERY shallow, barely deeper than the metal thickness.  The Motorola version of this tool has an optional collar, with a tooth that removes a thin line of paint which can help grounding.  Most modern NMO mounts have 'teeth' on their clamp, which makes a low-inductance ground connection, so this older hole cutter is now rarely used.

K5LXP:  "Body panel steel is pretty thin, and the torque you put on the punch could distort or crease the panel. "

The kind of punch used for installing an NMO is designed for this very purpose, and is a specialty item, unavailable except from a few dealers.  Greenlee radio punches are made to make round holes in display panels made of very light gauge, mild materials.  They leave a perfectly round hole with no torque crease at all, in materials as light as aluminum roof flashing.  This type punch, which has a die collar that prevents torque damage to the surrounding light-gauge material, could never be used by an electrician, and even a single attempt to use it on a breaker box would ruin it.  We're talking about two different tools, entirely.

"Punches are expensive too, compared to the antenna hole saw which is less than $15 retail. "

That I agree with, unless you get VERY lucky and buy your Greenlee radio punch "surplus" -- you can easily pay $50++ .  One good supplier I know charges $42 for one.
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N3ZKP
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« Reply #21 on: April 18, 2005, 03:54:14 PM »

<< That I agree with, unless you get VERY lucky and buy your Greenlee radio punch "surplus" -- you can easily pay $50++ . One good supplier I know charges $42 for one.   >>

True, and over the last 35+ years I figure my punch (purchased in 1966 for $9) has more than paid for itself. I long ago lost track of how many holes I made with it - has to be close to 150 by now.

The right tool for the job is always cheaper in the long run. Smiley

Lon
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AA4PB
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« Reply #22 on: April 18, 2005, 06:37:09 PM »

There's a special kind of hole saw made especially for installing NMO mounts
--------------------------------------------------
Then the people giving the advise to use a hole saw should specifiy that what they are talking about is a specialty item rather than the hole saw you pick up at Home Depot. Personally I think using a chassis punch is much less risky than using a common type of hole saw - but then to each his own. Of course if you have a special hole saw designed for NMO mounts then that's what you should use.

Chassis punches are something that anyone who does any home construction should probably have on hand anyway.
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ASTRODANCO
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« Reply #23 on: April 18, 2005, 07:29:49 PM »

Forget about Greenlee hole punches.  Using a hole punch is just going to make life more difficult that it has to be.  An NMO hole saw does a fine job in just SECONDS with no extra hastle.  Honestly!  I was told by one guy online to use a Greenlee hole punch as well, but I'm very glad I didn't.  It would have meant totally removing the headliner in my case -- not really a viable option so far as I was concerned.

IMHO, the way to go is to use an Antenex 3/4" hole saw.

I've installed two NMO mounts on my car.  I saved $240+ of labor cost (going rate for a professional installer) by doing it myself.  BTW, this was all much easier than it reads!

Here is what I did:

1. I purchased the following items:

a. One Antenex 3/4" hole saw. http://www.radiooutfitter.com
b. Two Antenex 3/4" NMO mounts with 17' RG-8X coax. See above.
c. Two Antenex NMO mount rain caps (for when no antenna is attached to mount).  See above.
d. Several 3/4" rubber NMO hole plugs just in case I ever want to remove the mounts.  See above.
e. One Antenex 800MHZ antenna and one Radiall-Larsen GPS antenna.  http://www.ameradio.com
f. Several six-piece BNC solder clamp connectors for RG-8X.  About $2 each.  http://www.wb0w.com
g. Coax stripper for RG-59 (same size as RG-8X).  Quality one, not cheap one.  Radio Shack.
h. One small pizza pie pan.  Target.
i. One short metal fish (fiche?) tape.  Home Depot.
j. One small stainless stell prybar (looks like a miniature crowbar).  Target.
k. Masking tape.  Target.
l. Black split-loom to protect the coax in certain locations, such as transitional areas and
under the dash.  Home Depot.

Already had wrenches, socket wrenches, star point wrench set, plyers, drill, soldering iron, solder, household vacuum cleaner, etc.

2. Gently rapped my knuckles down a line from the middle rear of the roof to the middle front of the roof to detect where metal crossbars that I would not want to drill through were located.

3. Removed all the floor, pillar and headliner trim from the passenger side of my car. I did this carefully with the prybar so as not to break the trim fasteners.  I also had to remove the front and rear handholds, B pillar seatbelt retractor mount, both interior ceiling light and the passenger side windsheild sun shade.  Removing all this stuff was time consuming.

4. Gently pulled down the headliner on the passenger side just far enough so that I could look between the headliner and the roof to confirm crossbar locations and other obstructions (such as wiring).

5. Put masking tape down a line from back to front of the roof. Carefully measured back-to- front and side-to-side for roof locations where I wanted to place the mounts.  I had to place one mount a few inches farther back from the ideal center location in order to prevent drilling through a metal crossbar. Placed more masking tape around the propective hole locations to protect the paint job.  Measured and remeasured.  I did not drill until I was happy with my propsective hole locations.

6. Drilled two holes in the pizza pan, threaded the fish tape through and tied the tip of the tape to one side with wire.

7. Gently shoved the pizza pan up above the headliner and below the roof so that it sat under the location where I was going to drill.  This was to catch the hot metal plug and hot metal shavings that would fall down while drilling.  I didn't want this hot stuff burning any holes through or melting my headliner, nor did I want a bunch of *^&(*&( metal filings stuck up there.

8.  Drilled the holes.  I used low RPMs with some pressure on the drill bit.  Piece o-cake!  Took maybe 10-15 seconds, if that.  Contrary to Antenex recommendations, I did NOT use drilling oil. (I didn't need to extend the life of the hole saw and didn't need an oily mess either, thank you.)

9. Vacuumed up the metal filings.  Gently pulled on the fish tape to remove the pizza pan.

10. Installed the NMO mounts into the holes.  The mounts already had to coax attached.  I put the coax through the holes and temporarilly out the passenger side of the headliner first, then dropped the mounts themselves into place once the coax had all gone through.  I had to be careful to keep the mount centered while screwing it down (from the outside.  I also had to be careful to keep the mount from rotating while I screwed it down.  I did this by using a felt pen to place a registration mark on the mount base and the car roof (to detect rotation) and another mark all the way around the mount base (to detect mis-centering).  Then I tightened it down with a wrench.  Note that the NMO mount has an o-ring in the base to seal it against leaking.

11.  Ran the coax above the headliner down the A and D pillers (my car is a wagon with A, B, C and D pillars).  I had to be VERY CAREFULL not to disturb the passenger side airbags which are in the headliner!  Had to be VERY CAREFULL not to run the coax too close to those airbags.  In the case of the coax running down the D pillar, that was not a problem.  In the case of the coax running down the A pillar, I followed the existing AM/FM antenna coax pathway.  (My AM/FM antenna is the Euro style mounted on the rear of the roof.)

12.  Ran the coax down the A pillar to the dash for one antenna and under the door trim up to the dash for the other antenna.  I put split loom over the coax wherever I thought it might be exposed to heat or any possibility whatsoever of abrasion or wear.

13.  Soldered on and cinched down the BNC solder clamp connectors.  Unless you've invested in a high quality crimper and learned proper crimp technique, I heartilly recommend the six piece BNC solder clamp connectors over crimp connectors.  They're very easy to put on, solder and then "clamp."  They're also removable and re-usable.  If you mess up, you can simply repeat until you get it right.

14. Connected coax to radio and tested.

15. Carefully put all the trim back into place, etc.  This part took a long time.

DONE!

When I sell my car I will remove the antennas and place the NMO rain caps over the mounts.  I will tell the buyers (as a selling point) that the car is both GPS and Cellular antenna ready!  If I find that buyers don't like the antenna mounts, then I'll remove the mounts, place the rubber 3/4" NMO hole plugs in their place, and say nothing about them.
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AD4U
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« Reply #24 on: April 19, 2005, 06:53:15 AM »

One more comment and I think I will have ridden this horse to death.  I have been a HAM for about 35 years.  I will be the first to admit that I am no expert on any subject. Over the years I have installed more mobile antennas than I can remember, built HF quads and Yagi beam antennas from scratch, home-brewed at least 10 different linear amps, and even a 20 meter transceiver (not from a kit but from an article in Ham Radio magazine).  I do this because I feel that my limited knowledge of the subject will give me a reasonable chance of being successful.

However a lot has changed in 35 years, at least from my prospective.  Today's vehicles are full of wires and sensors that can be damaged by someone who is not familiar with where they are located.  Head liners and door jamb trim strips used to be secured with screws or clips.  Now many are glued on.  Cars today have more insulation than in the past.  It is often either glued in place or simply sprayed on.  Sheet metal used in vehicles today is much thinner than years ago.  All of this and more can be easily damaged by someone, who is not familiar with the particular vehicle, sawing into the roof and trying to run coax

I recommended taking the vehicle to a two-way shop for these very reasons.  The local two-way shop charged me exactly $40 to professionally install a Larson NMO mounted 5/8 wave length two meter antenna (which I provided) on my new vehicle.  They ran the coax to the rig, and install a soldered PL 259.  I guess some shops charge $250 as stated in other responses.  If that were the case here, I may have tried to do it myself.

But when it came to cutting into the roof of MY new $45,000+ truck with a 3/4 inch hole saw, not bending the thin sheet metal roof while sawing (which would not allow the NMO mount to properly seal), properally installing the NMO mount, and running coax under the head liner down a door post to a rig located under the dash, I decided that there are some things better left to the professionals.

Reputable two-way shops have the experience, tools, and "know-how" to do the job right and the insurance to repair the vehicle if something is damaged.

Sincerely:

Dick

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K8LEC
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Posts: 64




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« Reply #25 on: April 19, 2005, 07:40:34 AM »

Thanks everyone for all the repsonses.  Great stuff!!  This topic will sure be a good one for others who might be as unsure as I was.  Good information from all!!  Thanks!

73
Lars
K8LEC
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K1CJS
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« Reply #26 on: April 19, 2005, 01:29:54 PM »

I agree with Dick, AD4U.  Today's cars are totally different from those of just a few years ago.  Extra wiring, sensors, air bags, etc., are just a few of the headaches you'll have to contend with in cars today, along with satellite radio and GPS systems.  It is well worth the $40 you'll spend to get the job done right AND have it guaranteed--in case something goes wrong and the car has to go back to the dealer, you'll be covered better if you have an installation invoice from a reputable radio shop in your hand instead of saying you put the antenna system in yourself.

To put it another way, either you pay them now or you may end up paying them much more later!
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AA4PB
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« Reply #27 on: April 20, 2005, 04:25:38 AM »

I'd be willing to bet that if you take your car back to the dealer for a problem that they can trace to the antenna installation, it won't much matter if you have an invoice from a reputable radio installation shop. They'll either want you to pay for the work or take it back to the radio installation people. The work won't be covered under warrenty just because you have that invoice in your hand.

How about a fixed station? Should we have our radios and antennas installed by a radio shop so that if there is a fire or other damage in the futue we'll have an invoice to prove we didn't do the work ourselves?

How about those of us who change our own oil or break pads? I guess that would be a big no-no.

In the last 10 years my installations have been limited to my pick ups. I don't know about all the fancy hi-end cars these days but I can assure you that with a pick up installing an NMO mount is just not that big of a deal if you have any mechanical ability at all.
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AD4U
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« Reply #28 on: April 20, 2005, 08:28:49 AM »

'Guess the ole horse we have been riding ain't quite dead yet.  I feel very strongly that HAMs should design build and repair their own equipment, build their antennas from scratch, erect and climb their own towers, etc as long as they feel they are competent and able to do so properly and safely.

Modern vehicles are complicated devices.  Deceleration sensors that operate air bags are located all through the vehicle.  Sensors for side air bags are located on the side of the vehicle.  Many if not most of these are located in the door jambs, not in the door itself.  Too many "g's" from opening and slamming doors might set the air bag off.

If you should accidently damage a side air bag sensor while snaking coax down a door jamb, either the side air bag would not deploy in a side-impact accident or you could set it off while running the coax.  Repairs including a new air bag assembly will be over $1000.

It is not my intent to take issue with anybody.  But I strongly feel that anybody, including HAMs, are better off paying a professional to do a job for us, if we do not feel that we have ythe knowledge, training, and tools, to do the job properly and safely.

Sincerely:

Dick
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K1CJS
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« Reply #29 on: April 20, 2005, 08:32:15 AM »

Bob, my comment was made to point out the fact that you will have more places to go to try to get the trouble fixed and not pay for it yourself.  FYI, most radio installation shops keep track of the bullitins concerning installation of auxiliary equipment in newer vehicles and will know if there are place to stay away from when installing antennas and such, especially with the amount of electronics in todays cars.  Face it, with air bags, satellite radio systems, GPS navigation systems, memory seats, memory pedal positioners and even more esoteric systems and add-ons, there is more than an even chance of interaction and damage, and if you have the installation was professionally done you can go back to the installer as well as the dealer to try to get satisfaction.

I to do my own oil changes and brake jobs, and even more on my car, but stay away from much of anything on my girlfriends car which is only a year old.  There is too much of a chance of inadvertantly screwing something up--I'll gladly pay for getting things done that I'm not sure of.

As far as home stations and other things, as usual you take comments to an extreme, but if you're not sure what you're doing wouldn't you have a professional install additional circuits in your home, or would you chance it and forgo insurance payment of a fire claim which was traced back to faulty electrical installation?  You can see this point fairly clearly, can't you?  Or are you going to stretch this one as well and say I'm talking about doorbell wiring?
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