Motorola (NMO) antenna mounts...

[MSS-Dave]

Need info on this. Sorry if it's in the search somewhere a few years ago though.

Motorola or NMO if you are a Larsen type mounts kind of guy.. vary between manufacturers. On some, the "button" on the center conductor of the mount is just a dot where the coax comes up and has a solder blob if you will. Some have a flat brass or silver plated surface there. My Motorola HAF 4016A mounts made by PC-Tel has flat brass for the center that's 1/4" in diameter. Seen some other brands that look close to 1/2" and many probably 1/8" for that "button".

Any issues with these differing sizes being used at specific frequency ranges? How about antenna types? Examples... The 800 1/4 wave for the above mount has the whip coiled flat where it contacts the mount the same diameter. What about using an antenna that has a spring loaded pin instead? (150 or 450 MHz) One that has the flat metal tab on a coil? (Larsen Low Band)

I've been doing testing on various mounts and antennas using a Anritsu SiteMaster to plot SWR curves and return losses and have seen some interesting stuff. Thought I'd ask those who have been through this in the field your opinion.

Assume the antenna will be mounted center of a metal roof on a standard pickup truck so GP shouldn't be a problem.

Thanks for the time...

Dave

[Tom in D.C.]

Dave,

Over the past twenty years or so I've probably had and used about fifteen various NMO mounts,
some with the antenna whip just twisted at the bottom end to retain it in the rubber thing and others,
the fancier ones, with the adjustable bottom with setscrew to adjust the length. In all that time all
of these various units worked fine with never a problem, so if I were a betting person I'd say that the
whip connection part of the setup, due to the design, is the least troublesome part of the whole system.

Regards,

[fineshot1]

I do concur with Tom on the commercial side, however for amatuer usage at 1.2ghz I had to make
my own nmo mount using LMR240 cable in order to get most of the rf to the antenna.