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Author Topic: Anybody here use 3/8" NMO mounts??  (Read 2198 times)
AB0RE
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Posts: 293




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« on: June 16, 2002, 03:02:11 AM »

I noticed they (Antenex, MaxRad, etc) make NMO mounts that require a 3/4" hole and ones that require only a 3/8" hole.  I'm wondering what kind of experiences people have had with each.

The 3/4" hole NMO mounts seem to be easier to install as they can be installed from above.  Most radio shops and people who I've run into seem to use these.

The 3/8" hole NMO mounts have caught my attention, though.  A 3/8" hole would be a bit gentler on my vehicle.  And, it appears that more of the mount comes in contact with the vehicle than with the 3/4" mounts, perhaps making the mount hold to the vehicle a little stronger than the 3/4" mounts.

Has anybody used the 3/8" mounts?  Are they stronger?  Why aren't the used more?

Thanks in advance for any replies.

Dan / ab0re
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K0BG
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« Reply #1 on: June 16, 2002, 11:47:01 AM »

The 3/8" clip-in mount I am familiar with is NOT an NMO, but like the NMO, it can be mounted from the outside just as easily as the 3/4" ones. The coax is harder to install, as it goes through the center of the mount. The bottom of the mount is "fingered" and it snaps into the 3/8" hole, then a ferrule is inserted to hold the clips against the edge of the hole. The Coax is then connected and the mounting ring screwed tight.

The 3/8" mount is fine, but it can pop out if it is hit hard enought (especially is the 3/8" hole is slightly oversized), or bumped repetedly over time. If you manage to hit an NMO hard enought to knock it off, something definately will bend or break!

Alan Applegate, KØBG
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N2HBX
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« Reply #2 on: June 16, 2002, 09:08:54 PM »

I have used the 3/8" NMO mount, and while the hole may be smaller, I agree with the previous post that thay can be knocked out fairly easily, and you may end up with a bigger mess than if you used the normal 3/4" mount.  The 3/4" mount distributes any shock to the antenna over a wider area and is much less likely to be pulled out and cause damage.

The 3/8" mount was OK for the old CB antennas with the skinny loading coils, but the antennas designed for NMO mounts are usually bulkier and require the better mount for proper support.

73, Larry, N2HBX
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AB0RE
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« Reply #3 on: June 16, 2002, 10:51:10 PM »

I'm not 100% sure we're talking about the same type of mount here.  The mounts that I'm referring to are a NMO mount.  They just require a smaller hole (3/8" vs 3/4").  Some examples of this are Antenex part # MAB8 and MaxRad part # MA38.  

Based on the photos I see, it appears that more of the mount comes in contact with the vehicles surfact than the 3/4" mounts.  With the 3/4" mount, there is only about 1/8-1/4" of the mount coming in contact with the underside of the roof around the hole.  With the 3/8" mounts, it appears that there is about 1/2" of the mount coming in contact with the underside of the roof around the hole.  

I know they do make some 3/8" hole NMO mounts that can be installed from above - they do look relatively flimsy.  However, the part #'s that I referenced above are for the mounts that require being installed from below as the bottom portion of the mount would never fit through a 3/8" hole.

Dan / ab0re
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K0BG
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« Reply #4 on: June 17, 2002, 09:40:27 AM »

Back in the old days, trucks didn't have headliners like they do today, and just about ANY antenna mount could be used. As two-way radios and telephones became d'rigor in cars which did have headliners, Motorola came up with the (N)ew (MO)torola mount which didn't require removing, or opening the headliner. Over the years, the patent has long since expired, and every antenna manufacturer has some form of it. It makes no difference which one you use; the most important part is: installing it correctly. If you can get to the bottom side, maybe you should look at Antenna Specialists' screw mount. You smack one of those off and a large chunk of the top will disappear!

As a sidebar, how many hams today know that at one time, you could order a zippered headliner? Or a cable conduit from front to rear? Or switched/unswitched 50 amp power cables? All as factory options.
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N3MG
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« Reply #5 on: June 18, 2002, 12:54:17 AM »

Dan-

I am very familiar with the standard Larsen 3/4" NMO, the Larsen 3/8" Thick Panel NMO, and the Antenex MABTO 3/8" Thick Panel mounts as I have had a special stake pocket antenna mount project going.

http://www.fastq.com/~louvu/antmount.htm

Follow the "Instructions" link on the above page to see the Antenex MABTO base in detail.

The Larsen standard 3/4" and the Antenex MABTO both use the "foot" style anchor on the underside of the panel.  The size of the foot is the same with both mounts so you bring up a valid point that with the 3/8" hole more of the foot is on the panel under surface compared to the 3/4" hole, which only leaves about 3/16" overhang on either side.  Mind you, the MABTO mounts from below, and the outer ring screws down over the top.

The Larsen 3/8" thick panel NMO base is more along the lines of what Alan is talking about.  This mount pokes through from above, exposing the threaded portion below.  They supply you with a brass nut to secure the base.  Not too bad, but the coax connection leaves something to be desired.  The center NMO contact is acually shaped like a silvered brad which you drive into the center conductor.  Another plastic sleeve slides over the center insulator and compresses the braid  against the side of the center hole of the mount.  A picture would be worth a thousand words here.  Another complaint is that it is not really designed for RG8-X which is so popular in mobile setups.

Larsen only makes the 3/8" thick bases as a kit with 17' of coax.  The Antenex MABTO is a solder connection, which will accept RG58 and RG8-X.  The mount is well made and has a silver-tinned ground lug. Antenex and Larsen make a ton of different mounts as you are aware.  I am partial to Antenex and they have  distributors- just call their main facility for one near you.

BTW, I have used the standard Larsen 3/4" NMO base in a thick panel, and had to over size the hole to 0.8125" to get the base in from below.  It has held up fine with a VHF/UHF dual band antenna on my truck.

73 Mark
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AB0RE
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« Reply #6 on: July 20, 2002, 12:46:57 AM »

Mark,

Thanks for the reply.

For those of you interested in a great side-view of the 3/8" NMO mount (showing how much more metal comes in contact with the roof), Mark has a good picture at:

http://fastq.com/~louvu/NMOfoot.jpg

Thanks again,

Dan
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