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Author Topic: NMO Mount Recommendation  (Read 669 times)
W7WHM
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Posts: 23




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« on: June 24, 2003, 02:25:17 AM »

Since NMO mounts seem to be the recommended way to go for mobile antennas I thought I'd stick a mount or two in the roof of my van.  This is an older van so poking holes and getting under the headliner is not an issue.  Frequencies of interest would be VHF/UHF.

I have two questions - what brand(s) would be recommended for a high quality mount?  I don't want a cheap imitation mount.

Second, I am not sure what an NMO mount looks like - what are the physical characteristics of the mating parts?  That is, what is the physical configuration of the antenna base and mating part in the mount?  I'm sure I've seen them, but I don't really know one mount from another.  I can't really tell from the catalog pictures I have seen.

Third (ok, so I was wrong when I said two questions) would be coax for a 10 or 15 foot run.  Is it worth worrying too much about type of coax (other than good brand) for 2m/70cm?

Last question is how come every time I do a search using the eHam forum search feature I never find anything?  I searched the MobileHam forum for "nmo mount" and didn't get a single hit, although I know there have been a lot of posts on the subject.

Thanks,
Wally
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K0BG
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« Reply #1 on: June 24, 2003, 09:05:44 AM »

The NMO (stands for new Motorola) uses a 3/4" hole and is designed so the mounting can be made from either side of the hole (makes mounting above a headliner easier). The mount is secured to the metal by a round brass ring about 1.25" in diameter. There is an o-ring under it, and when properly installed it is waterproof. The center of the mount is insulated. This portion then mates with a spring in the bottom of the antenna. The outer thread is obviously at ground potential.

Under most conditions, the RG58 (some makes use RG8X) is adequate. You can replace the coax with RG8 if you are careful, and I have seen a DYI article on doing this some time back, but I don't remember where.

As for the searches, well, if you don't just happen to select the correct search word, you might not find anything. Go to the articles section and look at the titles, then do a search on one of the main title words and see what you get. You'll find out that although the search engine is good, it doesn't check for content, just the title and these can be misleading.

Alan, KØBG
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K5LXP
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« Reply #2 on: June 24, 2003, 10:48:48 AM »

There is something *wrong* with the search feature here at eHam.  There are topics I've searched for that came up with nothing, even though I know they're there because I'm the one that wrote them.  I end up repeating myself in responses a lot because I can't reference the last post I wrote on the same topic, because I can't find it through the search.  A lot of topics are repeated regularly because the way eHam is set up, you can't easily dig through past questions and responses.  I kind of enjoy helping folks out and don't mind repeating myself over time, but just think if you could type "NMO Mount" and see the dozens of threads that already exist on that topic, you wouldn't have to post it again.  If someone could sort out all the topics ever presented here in the eHam forums, you'd have a complete FAQ for ham radio.

Oh yeah, NMO is definitely the way to go, every antenna manufacturer offers antennas made for this mount.  Don't worry about the coax, the 10 or 15 feet you would have isn't enough to matter much even if it's crappy line.  Most offer decent RG-58 (Times or Belden), so don't sweat it.

Mark K5LXP
Albuquerque, NM
k5lxp@arrl.net
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KE6PKJ
Member

Posts: 256




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« Reply #3 on: June 24, 2003, 01:22:45 PM »

You can also find special NMO mounts that fit in a 3/8" hole. If you've never seen a 3/4" inch hole in a vehicle, it can give you the willies the first time. It is a LARGE hole and some people prefer the smaller 3/8" hole. Easier to plug up if you remove the antenna but most people prefer to leave the mount in place when they sell the vehicle.
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KG4VJD
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Posts: 77




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« Reply #4 on: July 26, 2003, 07:50:44 AM »

I happened to have just put a 3/8" NMO mount on the roof of my old van.  I have been getting lots of replies from this forum about NMO mounts and finally made up my mind to drill a hole.  Sure enough, 3/8" hole is small enough for me to start with.

I installed the larsen 3/8" NMO mount kit.  The kit has full instructions on how to install it though it is lacking a few graphical illustrations.  But I managed to get the job done in about an hour.  I poped out the front ceiling light and drilled a hole there.  I ran the cable through the right side A piller to the dash.  After all, I connected a generic used dual band antenna (18" tall, with a 3.5 turn piggy tail in the middle) to the roof.  Without hooking up a SWR meter, I don't have an idea of the VSWR.  However, I am able to full quieting into my favorite repeater about 25 miles away using 1.5W.

Mark is right, a 1/4 wave on the roof is very efficient and my installation has proven this.

I'm thinking about to put NMO mounts on my other car too but it has moon roof.  I read the other post that it should clear the moon roof but I'm still unsure about the clearance (I have a 92 Nissan maxima).

73
Alex KG4VJD
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KG4VJD
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Posts: 77




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« Reply #5 on: July 26, 2003, 07:52:15 AM »

Oh, by the way, searchng a particular forum doesn't work.  I always ended up going up to the root of all the forums and start my search from there.  You'll get results from all forums.
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