NMO Shielded mounts ?

RadioSouth · Post by **RadioSouth** » Wed Mar 29, 2006 6:01 am

A few years back I was looking to pick up a Hirschmann fully shielded NMO mount (unlike most that have the RF connection to the antenna base
covered by nothing more than a piece of plastic). The idea was to minimize RF inside the cab. Then one of our board members Stan who was familiar with this item mentioned Hirschmann discontinued this item and now A/S carried it under KSM766. Searching recently I no longer saw it in the A/S catalog and assumed they canned it as well. So I found what I was looking for by a outfit called Eur-Am. I bought a bunch of these and installed one, problem was after the 1st rain after installing this I had a pool in my car. Install was good, hole was drilled with an Antennex hole saw and the Motorola brand NMO mount I had in this hole never gave me any grief in a couple of years. Now I see Radiall/Larsen carries this type of fully shielded mount and am thinking about giving it a try, anyone try these or having success with any other brand of shielded NMO mount ? (150/450 MHz)

kb0nly · Post by **kb0nly** » Wed Mar 29, 2006 9:22 am

I have used a few of the Larsen high frequency mounts which have the coax connection fully covered and crimped to the outside of the coax. I have used them on VHF and UHF and they work great to cut down rf interference inside the vehicle due to a rf leaky connection at the mount.

I replaced the traditional open style mount on one vehicle that was having troubles with the cruise control dying when you transmitted on VHF. There was a strong rf field around the bottom inside of the mounting location of the antenna that was apparently getting into the electronics inside the vehicle. After using one of the high frequency mounts the problem went away. For the slightly higher cost it was worth it.

I have one of these mounts on my van with an L-Bracket for the GPS antenna. Obviously putting one of these on a bracket is a lot better than using one that isn't sealed up and would be a good practice regardless of operating frequency.

RadioSouth · Post by **RadioSouth** » Thu Mar 30, 2006 6:53 am

Thanks for the response, hard to believe so many of the NMO mounts are still of this 'open' contact design in todays age of electronically controlled everything in our cars and the awareness to RF safety. (Interesting that most of the manufacturers have a closed contact on 800/900 mounts with the center pins but not on stuff designed for VHF/UHF). I'm going to try a couple of Larsens, on a Google search I only got hits from Hutton and Tessco on these, anyone have a preference of one over the other or is there someone else good that carries these ?

tvsjr · Post by **tvsjr** » Thu Mar 30, 2006 8:09 am

Tessco.

Hutton's moved to a truly screwed up pricing scheme. Unless you have a rolling average of $5K/year purchases (at your pricing tier), you pay damn near list.

Tessco requires $100 list every other month to get you to Gold pricing, substantially below list. I buy at Gold all the time, and rarely make it to Platinum ($5K/month).

You'll need to have a company/DBA and set up an account with them to place orders. You'll also have to go through the credit process, as their accounts are typically Net 30.

Tessco is *great* to do business with. Never once have I had a problem with stuff not arriving on time, them shipping the wrong stuff, etc.

kb0nly · Post by **kb0nly** » Thu Mar 30, 2006 8:10 am

Between those two i would probably have to recommend Tessco, but only because its the one of the two mentioned that i actually have experience with.

I would have suggested Waltel.com had he not gone out of business, that's where i got all my mounts and brackets.

Radiooutfitter.com is another one that i have used, they have the Larsen mounts.

K4RXR · Post by **K4RXR** » Thu Mar 30, 2006 8:12 am

Are you talking about the Larsen NMOKHF mount? I'm looking for a good source for them, too.

RadioSouth · Post by **RadioSouth** » Wed Apr 05, 2006 2:53 pm

I wound up with part# NMOKHFUD which is the NMO mount with 17' of double shield RG58 (no antenna or connector) which just arrived today.
I went with Radiooutfitter.com as reccomended by KB0NLY (thank you)
and I would recommend them as well. I don't have an ongoing need so I didn't set up an account with Tessco or Hutton and found Radiooutfitter.com to be within a buck or two.

While on the subject, I've installed a bunch of Motorola brand NMO mounts and they all came with a little pack of clear grease that I used to lube up the gasket prior to install. Sound like something an outfit like Napa would carry ? I'm assuming it's dielectric grease?
(Didn't come with A/S or Antenex mounts either).

apco25 · Post by **apco25** » Wed Apr 05, 2006 7:11 pm

Its silicone grease

Maxrad makes a fully shieded mount with a right angle SMA connector on it, the MMF series.

K4RXR · Post by **K4RXR** » Thu Apr 06, 2006 7:49 am

I ordered some Larsen NMOKHFDS mounts from Tessco earlier this week. No account necessary if you use a credit card. The DS cable is essentially the same as the UD cable, but uses a stranded center conductor.

Also, you should be able to find dielectric grease at just about any auto parts store (NAPA, Pep Boys, Autozone) since it's commonly used these days on spark plug boots because of the high under-hood heat and high-voltage secondary ignition systems on today's cars. I bought a tube of Permatex Dielectric Tune-up Grease at Pep Boys a few months ago.

Bob...