Users may not create topics, posts, or private messages containing or relating to the following material (especially pertaining to Motorola copyrighted software, unless you want Motorola to come along and shut this site down):

  • Listing for sale or trade of, or links to sites offering for sale or trade of, or giving away, Radio
    Service Software (RSS) or Customer Programming Software (CPS)
  • Profanity, pornography, defamation, or slanderous remarks directed towards any individual or entity
  • Commercial advertising (except in the Batboard Vendors forum, as approved by the Admin/Mod Staff)
  • Any other items which may be deemed as offensive

If any topics, posts, or private messages containing or relating to the aforementioned material are brought to the attention of the Admin/Mod Staff, they will be deleted.

Additional FAQ items appear here in Forum Rules. Please review them for posting guidelines and further clarification.

To spring or not to spring a Larson NMO antenna?

This forum is dedicated to helping people with questions about installing radio equipment in vehicles. This can include antenna installs, electrical wiring questions/problems, and mounting systems. Pictures of installs are welcome.

Note: Discussions regarding lighting, sirens, and other equipment now has its own forum in the 'off-topic' section below.

Moderator: Queue Moderator

Jonathan KC8RYW
Posts: 1747
Joined: Fri Dec 28, 2001 4:00 pm

To spring or not to spring a Larson NMO antenna?

Postby Jonathan KC8RYW » Sun Feb 09, 2014 2:31 pm

Planning a mobile install.

Since it's a hatchback with a sunroof, I'll be doing two L-bracket mounts near the hood with NMO's.

I'm planning on using Larson 5/8 wave VHF antennas.

Larson has optional springs you can buy.

What are the pros or cons to using springs?

Thanks, guys!
73 DE KC8RYW
Random Motorola Part Number:
SYN1894B - V3m Sprint-branded Battery Cover

User avatar
MSS-Dave
Posts: 767
Joined: Mon Jun 30, 2003 6:02 pm
What radios do you own?: XTL5K, NX300, PD782, Spark Gap

Re: To spring or not to spring a Larson NMO antenna?

Postby MSS-Dave » Sun Feb 09, 2014 2:49 pm

Pro: Might prevent breakage of coil IF you hit something low. If you are putting antennas on L brackets on the hood, if you hit something low enough to worry about the antennas, you will have more of a problem with your roof or your face as it hits whatever is that low.... :lol:

Con: Could cause noise or bad SWR if the braid inside the spring corrodes.

I personally have NEVER used springs on any VHF or UHF antennas. Never broke anything either, probably lucky though. Had 5/8 Larsen VHF and long ASP colinear UHF on top of a full size van for years. Just be aware of your surroundings and you should be golden.

dbartkowiak
New User
Posts: 7
Joined: Sun Dec 22, 2013 1:39 pm
What radios do you own?: CDM750/1250, Maratrac, Maxtrac

Re: To spring or not to spring a Larson NMO antenna?

Postby dbartkowiak » Tue Feb 11, 2014 10:14 am

We here in Western NY use low band for fire and public works. We quite often mount antennas with 42 inch whips on top of fire trucks and snow plows. On these high profile vehicles we always use a spring to help absorb the shock of tree limbs and overhead doors. Even with the springs, they still get damaged and sometimes even pulled out of the roof. I do believe the spring helps save the antenna in most cases. It does require periodic inspection to make sure the braid inside is not broken and the spring has not become an inductor.

Having said that, any antenna we install at trunk or hood level does not get a spring. As MSS-Dave points out, if you hit anything that low, your antenna is the least of your worries. It is not worth the price of the spring or the extra maintenance. As I recall the Larsen spring is a straight spring as opposed to a Spectrum spring that is tapered. It is more flexible and at highway speeds will flex more than just a whip. This could affect SWR as the antenna becomes closer to the body metal. We have noticed this at low band frequencies (46 MHZ). I suspect not so much at higher frequencies.

By the way, another tip from the land of salty roads. If you use an NMO mount on your right angle brackets, seal the base of the mount with silicone sealer. I had two antennas installed and one day one of the two radios started performing very poorly. When I went to connect my test cable to the suspect radio, I found the antenna connector crusted with salt. The salt water from the road got into the cable and migrated down the cable to the radio and then dripped out the connector. When I inspected the other antenna cable, I found the braid inside the cable was black up to about a foot from the radio. I suppose if you live in Arizona, you would probably never have this problem.

Solo
New User
Posts: 17
Joined: Tue Mar 12, 2013 10:36 pm
What radios do you own?: Astro Saber, Astro Spectra

Re: To spring or not to spring a Larson NMO antenna?

Postby Solo » Wed Feb 12, 2014 8:12 pm

My rule of thumb is that springs are only used to prevent or attenuate damage from trees, roofs, etc.

If your mounting is at the hood level, anything which the car will fit under is high enough that a spring probably wouldn't flex anyhow.

RadioSouth
Batboard $upporter
Posts: 2858
Joined: Mon Sep 03, 2001 4:00 pm

Re: To spring or not to spring a Larson NMO antenna?

Postby RadioSouth » Wed Feb 19, 2014 9:45 am

If the sunroof is the only thing keeping you from drilling you might want to pull the headliner to check clearance, it might fit near the back of the roof.
Different cars but I had over a foot of clearance on a Nissan Maxima that I installed an antenna on.
If you do a lot of highway driving you'll notice the spring makes the antenna bend more, performance has to take a hit when your antenna is bent 45 degrees.

SlimBob
Posts: 911
Joined: Thu Dec 18, 2003 11:38 am
What radios do you own?: I sold my soul for a Saber.

Re: To spring or not to spring a Larson NMO antenna?

Postby SlimBob » Sun Mar 09, 2014 11:34 am

I recommend putting a spring on the antenna if you're too lazy to get out and take it off before driving through the parking garage.
An armed society is a *polite* society.

User avatar
nukedude
Posts: 59
Joined: Fri Apr 16, 2010 9:40 am
What radios do you own?: Many Motorola's

Re: To spring or not to spring a Larson NMO antenna?

Postby nukedude » Wed Jun 18, 2014 6:48 am

Unless it is going on the roof of a fire truck or high profile vehicle, the spring is not needed. If you can drive through parking garages and not have the antennas hit something, then the spring is not needed. Where I work, we have hundreds of 1/4 whips for VHF and UHF in use. The very few that have springs are corroding as they tend to hold onto water more than the coat hanger whips. Simpler is better if the spring is not required.

Jim202
Posts: 3487
Joined: Sun Sep 09, 2001 4:00 pm

Re: To spring or not to spring a Larson NMO antenna?

Postby Jim202 » Thu Jun 19, 2014 5:17 pm

If your having damage done to the roof of a vehicle with the long whips hitting something, your not using a Larson NMO coil. Many years back I was taking care of a large fleet of cement trucks that were using ASP 3/4 inch mounts. These will do damage to the roof and tear them open like a tin can if the coil hits anything. Won't happen with the Larson coils. The brass ring on the inside of the coil will come out or the plastic will break long before any roof damage is done.

Cut the body work on repairing the roof of the cement trucks to ZERO after using the Larson coils and long whips.

Jim


Return to “Vehicle Radio Installs”

Who is online

Users browsing this forum: No registered users and 1 guest