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eHam Forums => Mobile Ham => Topic started by: VE3XKD on December 24, 2010, 02:02:43 PM



Title: Larson NMO died in Winter
Post by: VE3XKD on December 24, 2010, 02:02:43 PM
All

I had the unfortunate experience of my 25 year old Larson base coil shattering on me. I was driving into an underground garage and it was under construction and had lower than normal clearance at the entrance, I stopped, got out of the car, and twisted my Larson at the plastic base ad the whole thing shattered in my hand because the mount threads had corroded from all fo the salt the city spreads on the road here and the antenna had become stuck to the NMO mount. It was minus 15 C at the time. I was in a hurry and gave it my usual hefty twist to unscrew it and the plastic  just shattered.

I have a replacement Larson antenna, should I coat the mount threads with anything so this does not happen again.


Title: RE: Larson NMO died in Winter
Post by: K0BG on December 24, 2010, 03:44:14 PM
I always put a little silicon on the threads. I don't know what they do today, but they used to include it with the mount.

I've never had one shatter, even at -40°F, but being plastic, I suspect that could happen. Also, the newer stuff is all black, rather than gray, and perhaps that should tell us something.



Title: RE: Larson NMO died in Winter
Post by: KH6AQ on December 24, 2010, 04:37:03 PM
What might it tell us?


Title: RE: Larson NMO died in Winter
Post by: K0BG on December 25, 2010, 07:11:11 AM
If you dig really deep into Larsen, you'll find out that the black plastic is UV stabilized. I don't believe the gray plastic was.


Title: RE: Larson NMO died in Winter
Post by: KC7YRA on December 25, 2010, 08:03:33 AM
I have seen many antennas shatter at -40 or -50.  I have seen Larsens fail, but very very few.  Like Alan said, the new black plastic seems bomb proof.  The old gray that turned almost yellow in the sun would eventually fail spectacularly.

The worst I have ever seen were the Maxrads.  They have a metal threaded section that held onto the mount but allowed the plastic of the coil to attach to it.  The plastic was very thin on these threads and I replaced MANY that "popped" the threads at the metal base.

I have been playing with a few Antennex brand antennas and they seem eerily similar to the Maxrads.  My plan is just to stick to Larsen.

What has me really freaked is my Hi-Q 5/80.  I worry about hitting a tree with the huge whip when it is -40 or so.  It has been on the truck for several years without problem, but I am very careful when it is so cold.

Brad


Title: RE: Larson NMO died in Winter
Post by: VE3XKD on December 25, 2010, 10:06:12 AM
Many thanks for all the pointers. I suppose 25 years of service is good enough from one antenna.

My neighbor is going to lend me his heated garage with the 12 foot ceiling so I can do the work.

Merry Christmas all!

VE3XKD


Title: RE: Larson NMO died in Winter
Post by: W3LK on December 25, 2010, 02:43:36 PM
All

I had the unfortunate experience of my 25 year old Larson base coil shattering on me. I was driving into an underground garage and it was under construction and had lower than normal clearance at the entrance, I stopped, got out of the car, and twisted my Larson at the plastic base ad the whole thing shattered in my hand because the mount threads had corroded from all fo the salt the city spreads on the road here and the antenna had become stuck to the NMO mount. It was minus 15 C at the time. I was in a hurry and gave it my usual hefty twist to unscrew it and the plastic  just shattered.

I have a replacement Larson antenna, should I coat the mount threads with anything so this does not happen again.

Just curious ...

If you had the antenna on the mount, with the rubber gasket underneath the coil, how did road salt get on the threads? I've run my vehicle through car washes without removing the antennas and used 1800 psi power washers on the vehicle and have yet to get any water into the threaded area.


Title: RE: Larson NMO died in Winter
Post by: VE3XKD on December 26, 2010, 02:13:56 PM
I don't know. The antenna was tight, and I can see the gasket on the leftover mount part that is still attached to the mount. The temperature is going up this week to minus 1 C and I should be able to take it off and have a close look when i replace it.


Title: RE: Larson NMO died in Winter
Post by: N4MJG on December 27, 2010, 08:23:49 AM
I have never have  any problem with mine even it 17 degrees ! with no problem at all, i understand they no longer sell them is that true?



73
Jackie
N4MJG
WWW.N4MJG.COM
SKCC #7305
NAQCC #5233


Title: RE: Larson NMO died in Winter
Post by: K0BG on December 27, 2010, 09:37:24 AM
They no longer sell the gray plastic ones Jackie. I have an old NMO150, and it is still okay. It has turned yellow with age, but who cares about that?


Title: RE: Larson NMO died in Winter
Post by: N4MJG on December 27, 2010, 07:39:41 PM
They no longer sell the gray plastic ones Jackie. I have an old NMO150, and it is still okay. It has turned yellow with age, but who cares about that?

Alan,

I still have black somewhere is garage ,i took it off since i wreck other truck :(


Title: RE: Larson NMO died in Winter
Post by: KI4SDY on December 28, 2010, 06:33:51 AM
Larsen dual band with base coil $85.00. Pro Am all metal dual band with open wound air coil and stud mount $12.00 (they even threw in a magnetic mount that I am not using). My Pro Am is still working and will at all extreme temperatures! No weak plastic to break or enclosed coils to load up with water. :'(

    


Title: RE: Larson NMO died in Winter
Post by: VA3WXM on December 29, 2010, 06:10:57 AM
Yeah, I would say 25 years from a mobile antenna is pretty darn good!  And the comments about the plastic breaking down from UV is probably what happened.

I had a couple of Sinclair UHF mobile antennas that each developed a crack in the ABS plastic bases. None of my Larsens ever did that.