NMO Through-Hole Mobile Antenna Installation

Magnetic antennas have much to offer the VHF and above mobile operator[1].

They can blend in quite well on mobile roof tops with luggage racks and other items that help hide the coax.

Then, of course, there are roof tops where coax will… well… just not look very nice.

Such is the case with my 1998 Ford Taurus and my dual band El Cheapo mag mount antenna. It has and still can serve me just fine on 2m and 70cm. The magnetic antenna allows perfect positioning of your antenna in the middle of your roof. That’s good. However, when your car looks like this…

Read the article about NMO Mounts[2]

…it may be time to think of an alternative approach.

What about glass mount antennas?
I thought long and hard about a glass-mount window antenna. I don’t know enough about them to make an educated guess as to their efficiency. A friend praises his glass-mount’s ability to stay glued in place. A concern, antenna aficionado I am, is the less even pattern surely resulting from any side mounted antenna. The window mount was out.

Back to the roof.

A Hole in the Car?!?
Dare I punch a hole in the roof of my daily driver to install an antenna mount? Dare I? Well… I don’t drive a Lexus, I drive cars till they die and won’t be selling my current ride to anyone who is going to care about the roof. I am just another struggling victim of the current, so called, ‘economic thinkers’ currently in power. Thus, I continue to carefully maintain and drive a 1998 Ford Taurus with 200k+ miles. It’s a Taurus… who’s going to care about a hole in the roof. The through-hole mount was in.

NMO… a clear winner
After much discussion, purchase and evaluation NMO was a clear winner and the 3/8 inch version was my choice.

So here we go with the steps taken to install an NMO 3/8 inch mount in my Taurus roof top.

So there it is… my 2m NMO installation with LMR-195 coax and a 3/8 inch NMO mount.

What did I gain? Let’s compare…

  • I like magnetic antennas just fine, but I won’t miss the black cable laying on the roof top. Advantage Through-Hole NMO Mount.
  • I never once had a problem with the antenna blowing off the roof, but it is nice to know this is stronger. Advantage Through-Hole NMO Mount.
  • The NMO mount has teeth on the bottom piece which make a good firm connection to the metal of the roof top. This is certainly a great ground connection for the coaxial cable shield currents, but the capacitive coupling of a magnetic antenna works pretty well too. Advantage Neither.

SWR
Simple monopole antennas provide broad bandwidth and the 19.2 inch whip is no exception as shown here…

SWR Measurements of 19 inch NMO Whip ideally placed on mobile rooftop

SWR Plots this boring are the dream of every radio user. More details and measurements available on the next post.

Conclusion
This is a keeper. Plus the standardization of NMO provides a large number of various whips from many manufactures to try in the future. A dual-band model is the next logical step for my dual-band FM rig.

References:

  1. Magnetic Antennas Don’t Suck
  2. NMO Mobile Antenna Mount Options
  3. Laird NMO Mobile Antenna Mounts
  4. Antenna Measurements on Ford Taurus Roof
  5. Mobile “Installation Notes” by K0BG

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