NMO mount size + water leak possibility? - MobileHam Forum at eHam.net

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eHam.net Forum : MobileHam : NMO mount size + water leak possibility?

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NMO mount size + water leak possibility?	Reply
by WA1USV on May 4, 2002	Mail this to a friend!
In a previous post I had asked about antenna recommendations and think I now have that all figured out... now it's time to mount the thing! I am considering a fixed, NMO mount which means a hole in my new car (ouch!) What is the actual hole size of an NMO mount? If I get too nervous about this, I might just go with a truck lip mount, although I like the looks and "feel" of a perminant mount and when I trade the car, the NMO mount becomes a "cell phone antenna mount" -- already installed and ready to go! Also, if I go with the trunk lip mount, is there a possiblity of water leaking where the coax depresses the rubber seal? Tnx!

RE: NMO mount size + water leak possibility?	Reply
by KD5BFE on May 6, 2002	Mail this to a friend!
You are much more likely to have a leak from the hole drilled for an NMO than a trunk lip mount. A trunk usually has a trough around the top where water runs down the rear window down to the back of the car. It doesn't matter if the cable pinches the weather seal a little because the water usually isn't forced that hard against it. But an NMO mount on the roof or decklid can be a problem if the antenna is not tight against the top surface, if the gasket or O-ring is not lubricated with silicone and fails, or if the hole is drilled too big. I am thinking about drilling a hole in the roof as well, but I've heard good things about Radiall/Larsen antennas and mounts for water sealing and reliability. Also, FYI most new 2G and 3G wireless phones are not compatible with the old cellular "car phone" antennas unless they are in analog roaming mode, and that's if you can get antenna adapter. I have not been able to find a digital antenna with an NMO mount yet, either. So if you're planning on keeping the car more than five more years, forget the "mobile phone antenna" explanation. Buy an NMO hole plug when you buy the mount to seal the hole when you sell the car. By then the teenager buying your car won't care about the hole, anyway.

RE: NMO mount size + water leak possibility?	Reply
by WB2WIK on May 6, 2002	Mail this to a friend!
I disagree about the "water leak" thing. I've mounted NMO mounts in the center of the roof of every car I've owned or leased since about 1974 (a lot of cars) and never had any kind of leak -- where would the leak come from? You punch a hole, not drill it, for an NMO mount (drilling highly NOT recommended!), and the mount fits tightly in the hole with a rubber gasket and strong locknut. It's exactly as watertight as the hole for your broadcast whip antenna or any other hole for a factory-installed accessory. If you don't have the appropriate punch for the NMO, stop by any 2-way radio shop (check the Yellow Pages), they all have the punch and will do the job for you in five minutes. 73 de Steve, WB2WIK/6

RE: NMO mount size + water leak possibility?	Reply
by K9PO on May 6, 2002	Mail this to a friend!
>FYI most new 2G and 3G wireless phones are not >compatible with the old cellular "car phone" antennas >unless they are in analog roaming mode, and that's if >you can get antenna adapter. An antenna cut to work with a given frequency works regardless of the type of modulation used. Your analog 800MHz cellular antenna will transmit an 800MHz signal even if it is using a TDMA or CDMA 2G technology. I think you might be confusing the new PCS band phones that operate in the 1900MHz band. Those would require that you use a new antenna. It has nothing to do with the mode you are in. However since analog is only used in 800MHz and that is why you 800MHz antenna can be used when analog roaming with a 1900MHz phone. These phones are not just dual mode but dual band as well. Scott

RE: NMO mount size + water leak possibility?	Reply
by KD5BFE on May 6, 2002	Mail this to a friend!
As I said, you are MORE LIKELY to have a leak problem by drilling/punching a fat hole in your roof than with a deck lid mount. I didn't say it was definitely going to happen, rather I was saying if you screw up the hole or forget the gasket, you'll have a leak. I'm probably going to have a 2-way shop do this install for me, but I do have confidence in that mounting method. Also, it is correct that it doesn't matter what antenna type you have for a particular digital mode. We all know that it doesn't matter if a signal is digital or analog, it is the transmitting frequency that matters. If you try running a digital single band, or dual band phone in digital mode over the older style 800 mhz antenna, you'll nuke the cheap transmitter in that $200 PCS phone unless you can custom design a matching network for the antenna. It will work in analog mode over 800 mhz, but not neccessarily in digital over 1800 to 1900 mhz. Dual Band means that the phone is capable of switching from 1800 or 1900 mhz for PCS services (depending on your provider) to 800 mhz for analog when no digital signal towers are available.

RE: NMO mount size + water leak possibility?	Reply
by KA9ZIM on May 15, 2002	Mail this to a friend!
A properly installed NMO mount will not leak and will do less damage to your car in the long run. The typical NMO mount requires a 3/4" hole. But, most of the antenna mount companies make NMO mounts that only require a 3/8" hole. The small hole is easier to drill or punch, and provides more support for antennas larger than 1/4 wave. So I''d vote for the 3/8" roof mounted NMO. I have two on my car. Easy to install and no leaks.

RE: NMO mount size + water leak possibility?	Reply
by N3IVK on September 20, 2002	Mail this to a friend!
Go with the NMO. We have been installing them for years....no leaks. Mag mounts and trunk lip mounts are worse on a car than a NMO mount. Matt N3IVK Evans Industrial Communications

RE: NMO mount size + water leak possibility?	Reply
by N8IWK on October 10, 2004	Mail this to a friend!
I would definatly go with a permament mount nmo style antenna. I've had more damage done from magnet mount antennas than from permament mount antennas requring drilling a hole. I've had a Larsen mount on a vehicle for over 15 years, the vehicle is badly rusted out, started from the rocker panels and is working it's way up. I believe after the vehicle has completely rusted out that Larsen mount may be the last/only thing remaining...HI HI..

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