Ground Plane vs No Ground Plane Antenna

[nartmot]

Hello,

I am new to radios and got a little confused reading about ground plane. Basically, I would like to install a Midland MXT275 GMRS radio on my truck but I don't want to drill any holes in my body work for an antenna. Ideally, I would like to use a hood hinge mount, like the one shown here: 2016+ Tacoma Hood Hinge Ditch Light Brackets. I am a little confused about ground planes. Would a non ground plane or a ground plane antenna work better in this location? Note that the mounting point is slightly elevated above the surface of the hood.

The antenna I am interested in is this one: A1843B-50 Comtelco UHF 450-470 MHz 3dBd Gain 5/8 Wave 21" Base Load BLACK finish Mobile Antenna
For NGP, I am considering this one: 450-470MHz Phantom Elite UHF Antenna NGP | eBay

Any thoughts or opinions would be greatly appreciated. Thanks in advance.

 

[W8UU]

Anytime you don't drill and mount the antenna directly to metal, you're accepting a compromise in performance. The metal brackets, if mounted properly (as in, directly to the metal frame) should work well enough though.

"No Ground Plane" antennas are also a compromise, as is the shorter length of the Phantom Elite antenna you mentioned. Your best bet would be to use those brackets with the longer Comtelco whip antenna.

 

[vagrant]

I would use an NMO lip mount to get the antenna closer to the hood and use a Larsen or the Comtelco antenna. You will RX/TX best in the direction where you have more of the metal hood (ground plane).

If you want an antenna that will work better at that mount point for GMRS, I would use the Diamond NR770. It is twice as tall, but it works well.
Available in chrome or black. There is also an NMO version. Diamond NR770HA, Diamond NR770HB, Diamond NR770HNMO Antenna

P.S. You will may be inundated with members who disregard your want and tell you to drill a hole. Not that they're wrong, but you know....people.

 

[nartmot]

@W8UU @vagrant Thank you both. I appreciate the advice. I would love a longer antenna but I also want to avoid having to remove the antenna regularly due to garage clearance issues. It sounds like the Comtelco 1843 is probably going to give me the best compromise.

 

[mmckenna]

The antenna I am interested in is this one: A1843B-50 Comtelco UHF 450-470 MHz 3dBd Gain 5/8 Wave 21" Base Load BLACK finish Mobile Antenna
For NGP, I am considering this one: 450-470MHz Phantom Elite UHF Antenna NGP | eBay

Any thoughts or opinions would be greatly appreciated. Thanks in advance.

Mounting off the side of the hood will provide a lopsided ground plane and will result in the radiation pattern being skewed in the direction of the most metal. Ideal location is smack in the center of the roof, that gives the ideal ground plane.
If you mount it in the center of the roof, the 1/4 wave UHF antennas are only 6 inches tall, and probably won't have any issues with garage clearance.
If you mount it on the hood channel, you are likely going to get better performance from a half wave antenna, but having the antenna down below the cab is going to result in some shielding, really not the best place for the antenna to be.

Probably your best antenna choice would be one of these:

https://www.theantennafarm.com/catalog/laird-technologies-b4305cns-6072

https://www.theantennafarm.com/catalog/larsen-nmo450chw-833

But don't discount drilling a proper NMO mount. If you want the most performance you can get from your radio, you need to focus on the antenna install. Compromise mounts result in compromised performance.

 

[nartmot]

@mmckenna, So I need a NGP antenna to use my brackets? Is there a 2ft or less option you would recommend?

 

[N4KVE]

Generally a 5/8 wave antenna needs a ground plane while a 1/2 wave does not.

 

[mmckenna]

@mmckenna, So I need a NGP antenna to use my brackets? Is there a 2ft or less option you would recommend?

I'd recommend this one:

https://www.theantennafarm.com/catalog/laird-technologies-b4502ns-3235

It's about 12 inches or so tall.

I'm using the VHF version on a Polaris Ranger. Like the one I linked to, it's got the spring in the base. I'm running it off the back of the roll cage. I've hit some tree branches at 30MPH or so and other than a very slight bend at the top of the antenna, there's been no issues. I've had it on there for a few years, probably 1500-2000 miles of running trails with it.

Only concern with an antenna that short is that mounting it on the hood channel is going to result in shielding from the cab. It'll really work much better on the roof.

 

[nartmot]

Thanks @mmckenna . I took some additional measurements today and think I can actually make a 32" whip work, so right now I am leaning toward Laird B4505CS | 32 inch Chrome Base Coil Half Wave Antenna with NMO Mount and Spring Base - 450-470 MHz UHF - No Ground Plane Required | Arcadian Antenna. Its basically a black version of the one you originally recommended. No ground plane and the top of it will barely exceed the height of my camper shell, so it will act as a "feeler" for when I drive in low ground clearance garages.

 

[mmckenna]

Good deal.
And the spring at the base will absorb any strikes. I'm using a Laird antenna on my Polaris Ranger and it's taken some serious hits without issue.

 

[bharvey2]

I would use an NMO lip mount to get the antenna closer to the hood and use a Larsen or the Comtelco antenna. You will RX/TX best in the direction where you have more of the metal hood (ground plane).

If you want an antenna that will work better at that mount point for GMRS, I would use the Diamond NR770. It is twice as tall, but it works well.
Available in chrome or black. There is also an NMO version. Diamond NR770HA, Diamond NR770HB, Diamond NR770HNMO Antenna

P.S. You will may be inundated with members who disregard your want and tell you to drill a hole. Not that they're wrong, but you know....people.

I've used a couple of Diamond NR 770 antennas for compromised ground installations. They seem to work well.

 

[vagrant]

I've used a couple of Diamond NR 770 antennas for compromised ground installations. They seem to work well.

Yes, they do. I use one on a Diamond motorized mount connected to a luggage rack up on top and the other is low on the rear corner hatch of an SUV for 5W APRS transmitter.

For GMRS I actually use a Comet SBB-2 on the other side of the rear SUV Door and it is also below the roofline, as intended. Mainly so that I can get into the garage, but also to not cause myself grief with the TX/RX antenna up top. This Comet is connected to a dedicated UHF radio for GMRS and Ham P25 stuff. We are rich with repeaters in my area at 3k to 6k feet, so it does not take much to use them. I also rarely use GMRS or P25 simplex. Still, I guess I should grab another Diamond NR770 as a spare, or if I wanted to swap it with the Comet for improved service range/simplex on a trip.