Changing NMO whips

[WRTZ750]

I wanted to run this idea by the experienced antenna gurus to see if this would work.  I'm looking at getting an NMO Laird UHF antenna that says it's 12.5 inches long, but then lower down in the specifications page it says it's 15 inches long.  My idea is to have a Laird NMO magnetic mount on the car and be able to run the shorter Laird antenna on that but then purchase the Midland mxta26 whip that's about 32" long and when I'm using the truck I can remove the shorter Laird antenna, put the Laird mag mount on the truck and spin on the longer Midland antenna.

Would this work since it's an NMO whip going on an NMO mag mount or would the brand difference between the Laird mag mount and the Midland whip be an issue?

[marcspaz]

Can you provide a link or part number for the Laird antenna? Want to be sure I understand what part we're discussing. 

[WRCZ387]

If I'm understanding you correctly [if I'm not, please tell me], you want to change back & forth between two different NMO style antennas on a NMO magnetic mount

Yes you can: I have a Jetstream brand NMO mag mount, & I've interchanged a Larsen tri-band, a Larsen quarter-wave, now I have an E/M Wave tri-band, & an E/M Wave quarter-wave, all four fit the mount

NMO is NMO physically, at least on the antennas & mount that I have

[wayoverthere]

10 hours ago, WRCZ387 said:

If, I'm understanding you correctly [if I'm not, please tell me], you want to change back & forth between two different NMO style antennas on a NMO magnetic mount

Yes you can: I have a Jetstream brand NMO mag mount, & I've interchanged a Larsen tri-band, a Larsen quarter-wave, now I have an E/M Wave tri-band, & an E/M Wave quarter-wave, all four fit the mount

NMO is NMO physically, at least on the antennas & mount that I have

Agreed...I have Midland and browning nmo mag mounts on my truck that have hosted a variety of nmo antennas, including a laird 5/8 wave, Midland 3db whip, laird and Midland 1/4 waves, a couple different comets, a signal stalk, a tram, and a pctel for 6 meter.

On the length question, I agree with Marc....need more info to say for sure. One possibility is measurements of the whip alone compared to the whip+loading coil base.

[WRTZ750]

Sounds like this is something I can do then.  Here is  a link to one of the antennas I was looking at.

https://www.arcantenna.com/products/laird-bb4502n-12-5-inch-uhf-whip-antenna-with-black-nmo-base-450-470-mhz

 

I just added the link below as this antenna looks to be shorter at 11 inches and would clear the garage opening unlike the link below.  In your experiences is there increased road noise on antennas that use springs?  They mention that in the Laird website.

https://www.arcantenna.com/products/laird-antenex-bb4503s-450-470-mhz-mobile-base-coil-nmo-mount-antenna-with-spring-metalic-ground-plane-required

 

To account for garage opening clearance I suppose I should add about an inch to the overall height to account for the height of the magnet mount off the top of the vehicle as well, correct?

[wayoverthere]

3 hours ago, WRTZ750 said:

Sounds like this is something I can do then.  Here is  a link to one of the antennas I was looking at.

https://www.arcantenna.com/products/laird-bb4502n-12-5-inch-uhf-whip-antenna-with-black-nmo-base-450-470-mhz

 

I just added the link below as this antenna looks to be shorter at 11 inches and would clear the garage opening unlike the link below.  In your experiences is there increased road noise on antennas that use springs?  They mention that in the Laird website.

https://www.arcantenna.com/products/laird-antenex-bb4503s-450-470-mhz-mobile-base-coil-nmo-mount-antenna-with-spring-metalic-ground-plane-required

 

To account for garage opening clearance I suppose I should add about an inch to the overall height to account for the height of the magnet mount off the top of the vehicle as well, correct?

An inch for the mount is a good buffer...I want to say mine are about 3/4". On wind noise, mine isn't the best vehicle to judge this, since it has an aftermarket exhaust (not all that quiet). That said, I've only ever noticed minor differences in noise between the antennas in the windiest conditions...the comet and Browning have tight springs like that 2nd you linked, but they're also both in the neighborhood of 3' tall, with phasing coils along the way. I've run the 70cm tuned version of that first laird and never noticed any noise, and wouldn't expect a difference from that tight spring on the 2nd...good performance too.

[WRTZ750]

Thanks for sharing your experiences.  I see there is mention about a "pull tab" on these NMO mounts.  From what I can gather it involves the interface between the mount and the bottom of the antenna.  I thought I saw something about needing to make sure the pull tab is open/out of the way when connecting the base and antenna?  Anyone familiar with this?

Again, thanks for the help!

[gortex2]

Just drill a hole and drop a 1/4 wave on it. 99% of the time that will outperform what you need and not require removing it daily t go in a garage. 

[wayoverthere]

4 hours ago, WRTZ750 said:

Thanks for sharing your experiences.  I see there is mention about a "pull tab" on these NMO mounts.  From what I can gather it involves the interface between the mount and the bottom of the antenna.  I thought I saw something about needing to make sure the pull tab is open/out of the way when connecting the base and antenna?  Anyone familiar with this?

Again, thanks for the help!

If I'm looking at the right mount, the pull tab is for removing the mount from the vehicle... doesn't appear related to attaching the whip to the mount.

https://www.arcantenna.com/products/heavy-duty-mag-nmo-mount-cb-vhf-uhf-gmrs-radios-pl-259-rnmom195sumb12ist

 

https://cdn.shopify.com/s/files/1/0345/4055/2323/products/RNMOMMechanical_0db1632b-8a21-49d5-8f0e-d90c3ad34486_900x.jpg

[WRTZ750]

Thanks for that.  Yeah, drilling holes in roofs of cars doesn't fly with the other half.  Hence the magnet.

I am curious how 1/4 wave vs base loaded coil antennas differ.  All I know is the 1/4 wave antennas are shorter so my limited knowledge makes me think they don't transmit or receive as well.  I don't have ham knowledge so this may seem elementary to some but that's the extent of my antenna knowledge.  

But I'm here to learn.

[wayoverthere]

The 1/4 wave are effectively half of an antenna, using the metal mounting surface as the other half (ground plane), similar to the 12" spring antenna you linked. On the other hand, the first one linked (the 15") is a half wave, effectively carrying both halves, which is why it mentions not needing a ground plane.

The"base loaded coil" is a way of making it act the same size to the radio, while allowing it to be downsized physically, to some extent. Signal wise, generally the pattern may be a tiny bit less vertically on the base loaded compared to the 1/4 wave, but marginally further in distance...one of those things you'd find if you were on the fringes of range.

I've had no clearance problems with 1/2 or 5/8 wave uhf antennas, even in the 7' clearance garage at work, though it doesn't park indoors at home. For reference, mine are on the roof of a single cab, mid 2000's 2wd Ranger clone.

In terms of cable run from the magnet, consider your routing carefully to protect the paint, and protect the cable from pinching or kinking. If you're running it in inclement weather, watch the routing for water intrusion as well. I routed mine along the doorframe to the bottom, and turn upward to cross the seal...on the car, similar concept along the trunk seal, though I do have to be careful closing the trunk.

[WRTZ750]

Thanks for taking the time to explain things to a newbie.

[wayoverthere]

29 minutes ago, WRTZ750 said:

Thanks for taking the time to explain things to a newbie.

You bet. The fourm has been (and continues to be) a great resource for me too, and I try to return the favor when I can .