NMO mounts and coax for mobile installs

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astrodanco

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So what do you guys/gals think of 3/8 hole NMO mounts as opposed to 3/4 hole NMO mounts? I've been told that the smaller 3/8 hole makes the mounting significantly stronger.

While we're on the subject, what do you think of RG8X coax in mobile installations? I know, it's solid core. But man, the loss is so much lower. As long as I'm adding a NMO mount GPS antenna using RG8X, it would seem appropriate to just install all my NMO mounts with RG8X. Antenex also sells mounts with a (stranded core) Teflon coax that has low loss, but not as low loss as RG8X.
 

SCPD

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I've used 3/4'' NMO mounts exclusively and I've never had a strength issue. I suppose it depends on how large your antenna is and if there's a possibility of it being struck by tree limbs, etc. I also use the NMO mounts that are made for thick surfaces and sandwiched a plate of 16 gauge steel between the headliner and the roof surface. I can pull on the antenna with my bare hands without any flex of the roof surface.

Comparing loss figures for RG58, RG8X, RG214, etc. are probably not noticable in a mobile application because of the short lengths. I'm using Antenex brand RG58 coax (17 ft length) that was attached to the NMO mounts. I haven't noticed any signal loss and I can monitor a trunked radio system, with my Larsen Tri-band antenna, from 20 miles away. If you're using it for VHF/UHF a good quality RG58 will work fine. When I was running an H.F. mobile rig I used RG214 so that it would handle the transmit power effectively.
 

astrodanco

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frootydawg said:
If you're using it for VHF/UHF a good quality RG58 will work fine.
I'll be putting either a VHF/UHF/800Mhz antenna or just an 800Mhz antenna on one NMO mount and a (~1500Hhz) GPS antenna on another NMO mount. The first antenna will likely scrape my garage roof twice a day. I'd rather not throw away signal if I don't have to, particularly with the tri-band antenna which according to the specs is already -7dbi down on one of the bands (and this is a good antenna). The extra cost of 8X is just a few bucks, so I guess the only real question there is whether or not I'll be shooting myself in the foot by trying to install a solid core coax in a mobile installation (e.g., is 8X too easy to crush, bend too much, etc)? If 8X is too touchy, I should probably use Antenex Teflon coax instead.
 

LarrySC

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At the www.bncantenna.com site the NMO L-brackets are 3/8" Not one problem in 10 years. The RG-58 for cell/800 installations is better than 58 used years ago for mobile CB. The secret is a max length of 17'. If you install an antenna with 3db gain then you loose that at 17'. That puts you back to -0-. BUT if the coax run is longer than 17' you go in the hole on signal. If the run is shorter that 17' then you are ahead of the game. Good Luck, Larry
 
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