Switching to GMRS - Antenna grounding, choice, mounting, and more questions.. please help!

[In.The.Wild]

This is my first post to this forum, but I've been reading threads for a little while now and wow... I've learned a lot already.

Sorry in advance for the long post. I just want to lay everything out there to make sure I don't miss anything and hopefully make some good decisions with this purchase.

I am going to be switching from CB to GMRS. I've settled on the Midland MXT275 MicroMobile radio. My initial plan was to use the MXTA25 3dB ghost antenna for my every day / daily driver setup so I can fit in my garage, and then switch to the MXTA26 6dB whip antenna for wheeling trips. I would be connecting via the MXTA24 low profile NMO cable and mounting the antenna on a rear door hinge mount I already have installed on my FJ Cruiser (pictured below).

This is where things get a little fuzzy for me. I've had grounding\rust issues with this mount (carbon steel FJ Cruiser rear door hinge mount) and I want to do whatever possible avoiding them in the future with the move to GMRS. I called and spoke with a Midland rep who told me that I didn't need to worry about grounding with either of my antenna choices, but couldn't really explain anything past that. I've emailed Midland and haven't gotten a response, and I've read and watched about everything I can find on the subject.

From what I can gather (still probably wrong) the Midland antenna's I'm looking at are 5/8 wave which along with the 1/4 wave GMRS tuned antennas do require a ground plane. I've learned with CB radios that the antenna ground is of prime importance and you need a solid metal to metal connection from between the cable and antenna and the mount to the chassis to facilitate that ground. With a lot of the GMRS antenna installs I've looked at, and install instructions I've read - I haven't seen anything focusing on ensuring that the mount has exposed metal and where the mount attaches to the vehicle has exposed metal like what I see with CB antenna installs. I know there is a difference between RF grounding and electrical grounding, but don't have great grasp on the difference so I'm not sure if with GMRS antennas an exposed metal ground between the antenna and cable, and then mount and chassis is needed and/or as vital. I believe that the NMO style mount has teeth that bite into the metal mount, but I don't see people worrying about grounding the mount to their body or frame..

From what I now understand, the 1/2 wave length GMRS tuned antennas are a no ground plane style antenna so I wouldn't need to worry about the grounding of my mount. So I've started looking at the LAIRD BB4502N 12.5 UHF whip antenna. I'm hoping to get opinions on if this would be a better fit for my intended mounting location, and avoid the worry about the ground between the cable/antenna and mount/vehicle.

I'm also a little confused on antenna height requirements on the location of the vehicle. I see people mounting ghost style, and other small GMRS antennas on mounts next to their windshields between their hood and cowl and leaving positive reviews on performance. I understand that the higher the antenna, the less obstructed the antenna is, and apparently often the more centered on your vehicle the antenna is - the better. Which for me, I do not want to mount an antenna on my roof for a number of reasons, primarily with a roof rack and 35'' tires I can barely fit in the garage as is, and even with my current 3ft CB firestik antenna I'm having to get out and attached it to something to get in/out of my garage so I would love to find a way to avoid that with my GMRS setup which is why the ghost antenna was appealing.

I'm also a little confused not the different mounting style of GMRS antennas vs CB. From what I understand, the Midland MXTA24 low profile cable works with both a 3/4 and 3/8 mounting hole, which should work with my current CB antenna hinge mount as I believe that is a 3/8 mounting hole. Where I'm confused is on the antennas compatibility with both mounting hole options. For example, the Laird whip antenna, mentioned earlier, states that it works with a 3/4 NMO style mount pattern - would that work with the Midland cable and my current mount?

Finally, with CB antennas, you're expected to tune them. From what I've read on products descriptions and installations, GMRS antennas are often pre-tuned. Is this accurate, or just marketing? If it is accurate, would I need to tune any/all of the antennas I'm looking at and is that done on these by cutting the antennas?


Hopefully I can get some of these questions answered so I do not waste more money, time, and effort switching to GMRS than needed.


To re-cap some of the main questions -

* Will the Midland antennas work ok on my current antenna mount location, and will they ground through the mount and if so will the mount need a solid body/frame ground? If not grounded correctly, will this damage my radio like a CB radio can get damaged when the cable/antenna isn't grounded correctly?

* Based on my described setup, do you think any of the mentioned antennas will work? If I cannot get better reception than a GMRS handheld, I'm not sure this is worth the effort.

* Would the Laird antenna work with the mount, and cable I've listed, and eliminate the need to worry about grounding between the cable and antenna to the mount and the mount to the vehicle - and if so would an antenna of this height, work well in this location?

* Do these antennas need to be tuned?

* Is there anything else with this that I'm not thinking to ask?


Here are links to all of the products mentioned, if that helps anyone answer any of these questions.
Radio -

MXT275 MicroMobile®Two-Way Radio

The Midland MXT275 MicroMobile two-way radio offers 15 GMRS channels, a powerful USB-C charging port, NOAA weather alerts, & more. Order yours today.

midlandusa.com

MXTA24 Low Profile Antenna Cable -

MicroMobile® MXTA24 Low Profile Antenna Cable

Shop for the MicroMobile® MXTA24 low profile cable at Midland Radio. This antenna cable connector features quality shielding and removable UHF connection.

midlandusa.com

3dB Ghost Antenna -

MicroMobile® MXTA25 3dB Gain Ghost Antenna

Ensure a solid connection to your vehicle with the Midland ghost antenna. The MXTA25 3dB gain antenna is 3.5 inches in length and 1.5-inch base diameter.

midlandusa.com

6dB Whip Antenna -

MicroMobile® MXTA26 6dB Gain Whip Antenna

The Midland MicroMobile MXTA26 6DB Gain Whip Antenna quadruples signal output and is great for off-roaders, farmers, and more. Buy now at Midland Radio.

midlandusa.com

Laird NGP Antenna -

BB4502N 12.5 Inch UHF Whip Antenna with Black NMO Base - 450-470 MHz

The Laird 15 Inch UHF Whip Antenna features an elastomer spring that provides increased flexibility, better shape retention and eliminates electronic & road noise when compared to stainless steel springs. This antenna does not require a metal ground plane. *This Antenna Requires a NMO Mount...

www.arcantenna.com

Current CB antenna mount that I would like to use for my GMRS antenna.

 

[BigDaveZJ]

Why not just mount the ghost antenna off the roof rack or drill through the roof? Not everyone has GMRS so there will likely come a time when you will still want CB.

 

[In.The.Wild]

Why not just mount the ghost antenna off the roof rack or drill through the roof? Not everyone has GMRS so there will likely come a time when you will still want CB.

I can’t mount an antenna to the roof rack as I can barely fit I my garage as is, and I don’t want to mount it to the roof as I am going to be getting a new roof rack in the coming months and don’t want to obstruct where that will go.

I thought about using a different mount between my hood/cowl but I like the rear door hinge mount better as it’s more protected from trees and such, and I already have it installed... so if possible, I’d like to try and find a way to make it work.

Most the people I go out with are now switching to GMRS, and I am just not a huge fan of CB. So I am not worried about replacing it.

 

[BigDaveZJ]

If you mount the ghost antenna to the rack, you can keep it low enough.

Most people I go out with are GMRS too, but on the way to and from the trail being able to monitor CB is nice.

 

[In.The.Wild]

If I mounted it a lower cross bar, I *might* be able to fit in the garage. As is, I’m cutting it super close. However, the OEM FJ rack cross bars are a plastic material. How would grounding work?

 

[Billoftt]

I would just get a cheap NMO bracket like this.

Amazon.com: Midland Universal Roll Bar/Mirror Antenna Mount with NMO Connector - Works with Midland MicroMobile MXT105, MXT115, MXT275, MXT400 : Electronics

Buy Midland Universal Roll Bar/Mirror Antenna Mount with NMO Connector - Works with Midland MicroMobile MXT105, MXT115, MXT275, MXT400: Radio Antennas - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

Put one of these cables with NMO in there. Make sure you do a good job waterproofing the bottom part where the center element and braided shield is soldered into the mount.

Amazon.com

After that, get whatever antennas you want. However, my personal preference is to go as simple as possible by getting a simple 1/4 wave antenna. A 1/4 will need a ground plane, but it would be only 6.5”. It doesn’t specify on Midland’s web page, but a phantom antenna in the 450-470 range usually requires more. The phantom on my van specifies 20” plus they are significantly more expensive, so unless you really like the aesthetics go with a normal 1/4 whip.

Amazon.com: Tram 410MHz-490MHz Pre Tuned NMO Antenna (1126-B): Sports & Outdoors

Buy Tram 410MHz-490MHz Pre Tuned NMO Antenna (1126-B): Radio Antennas - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

At that price you can grab 2 and leave one in your glove box as a spare. These are significantly more durable than a phantom. A branch hits a whip, the whip just glides right under. A branch hits a phantom, it gets broke off. Then again I life in the Southeast US so that may or may not be an issue for you.


Sent by electrons or some crap like that.

 

[Billoftt]

Well, a lot of people responded during the extended period of time it took me to hit “reply”

Anyway, maybe go with a fender/ hood channel NMO mount like this.

Amazon.com: L-Bracket 1255 3/4 Hole Stainless Steel NMO 3/4 Hole Mount L Bracket Mobile Antennas Motorola Kenwood Vertex HYT for UHF VHF Coax NMO Mount Cable Mobile Antennas Car Truck Hood install by tram-browning : Electronics

Buy L-Bracket 1255 3/4 Hole Stainless Steel NMO 3/4 Hole Mount L Bracket Mobile Antennas Motorola Kenwood Vertex HYT for UHF VHF Coax NMO Mount Cable Mobile Antennas Car Truck Hood install by tram-browning: Antennas - Amazon.com ✓ FREE DELIVERY possible on eligible purchases

www.amazon.com

Then get a 1/2 wave or a 5/8 over 5/8 antenna. You could also get a Larsen NMO2/70B. It has enough bandwidth to in the 462 range (I checked) and if you ever graduate to Ham radio you got the best antenna ever already there.

Larsen NMO2/70B

https://www.theantennafarm.com/catalog/larsen-nmo2-70b-1712

A veritable cornucopia of UHF antennas. GMRS is 462/467 MHz. The antennas listed in bandwidth ranges such as 450-470 MHz are compatible with GMRS

https://www.theantennafarm.com/catalog/antennas-191/mobile-antennas-192/380-512-mhz-uhf-196/

Sent by electrons or some crap like that.

 

[In.The.Wild]

One of the pictures of that mount, that I’ve listed below, perfectly illustrates one of my questions - for GMRS antennas that need a ground plane, they do not need a bare metal contact point between the antenna/cable and then mount/vehicle to achieve that?

and in that picture, it’s connected to a roll bar - so it’s an antenna that needs a ground plane, apparently a large ground plane, it doesn’t have a direct metal to metal way to reach even the roll bar - how does that work?

 

[nwoods]

I am a licensed HAM operator, but that only means I passed a test, i truly dont know anything and seldom use my radio anymore.

With that disclaimer out if the way, here’s what i can offer:
1. Ground plane is imaginary, and basically means that your RF signal won’t go down, so all the physical energy goes up and outward. Hoods and Roofs make excellent ground planes. Antennas mounted on front bumpers work okay, but better rearward than forward. The hood (ground plane) is behind the antenna. Good for trail leaders.

mounts at your a pillar are also okay, but di suffer some immeadiate shielding from the cab towards the rear.

anntennas mounted on the rear really need to stick up above the roof. The length above the roof is the only part that benefits from the ground plane created by the roof.

each transmission wavelengthhas a physical length. Antenna length is designed to match that frequency sine wave length. Antenna cable length between transciever and antenna is also a specific length based in frequency range

physical grounding .... I dont know. I dont think thats an issue with non-powered antennas but i really dont know. For me, grounding was only an issue with power to the transceiver and a good solid connector on both ends of the antenna cable.

CB and GMRS are diff freq’s, shoukd have different antennas, amd possible different cable lengths. A one size fits none may not be ideal for range, but might be passible if everything else is really good.
there is a forum of a bunch of old guys who absolutely know their stuff, and are shockingly opinionated about HAM topics. For some reason the organization name is escaping me right now. Im sure its easy to find if you search ham radio forum, but im tapping this out on my phone and dont want to switch pages to look it up for you.

good luck, amd im sure someone who knows something will point out all my mistakes. Listen to them, I am probably wrong

 

[Longrange]

I believe the GMRS antenna gets its ground from the radio through its coax. Probably why the tech said it wasn't a problem. The amount of metal the antenna is surrounded by (ground plane) is a reflector and receiver of the signal transmitted by yourself and others. Therefore, if you wish to receive and transmit better, mount it anyway you want free of obstruction, aka. higher clear field of view. The length of the wave, I think with GMRS, is a few inches VS feet with CB and HAM. Therefore only a circle of reflective metal is needed to send and receive a good signal. I think good antenna manufactures build this into their antennas, with math and magic. GMRS doesn't propagate as well as CB or HAM because the frequency doesn't bounce as well as longer power waves. CB is a good choice for mountains and valleys but lacks power, Ham is way better because of propagation and power, GMRS is good for long distance, open areas, and now with less restriction on power (50Watt) and being fairly reasonable pricing, its a good choice. So to summarize, if the people in your group say they can't hear you, move the antenna higher. I really don't think you mounting it on the hood, rear deck, hinge or wherever your heart desires will make to much difference because people use a hand held with low power in the cab of their vehicle with great success. Good luck and just enjoy the drive.

 

[DaveInDenver]

We don't do any favors by using terms indiscriminately, such as "ground" in this case. Ground, as in the Earth, plays a role in the radio arts but here it's best to use it carefully.

You need circuit returns, which is what the "ground" means for the electrical feed line (connectors and coax) and antenna. Ground is understood to be the vehicle chassis and that's significant because the radio uses the vehicle as a power and RF reference.

The circuit in the radio that is imposing energy on the coax needs the circuit to be complete all the way to the antenna with a consistent impedance of 50Ω. If anywhere along the path up to and including the antenna itself is anything other than 50Ω the RF energy will be stymied. We see this measured in the reflection of EM waves back from what we call a discontinuity.

The radio connector has a center and outer contact that match the coax center and shield conductors. So far the circuit has both signal and return for the circuit. When it hits the antenna it might see various things such as a SO239 like the radio, an NMO, a 3/8" stud, two terminals. In most vehicles the antenna itself is only half of the true antenna so for the circuit to be complete the return side of the circuit needs a good path to the vehicle chassis.

If the whole electric circuit is done properly you may successfully energize the antenna such that it may be successful in radiating an EM wave into space.

For an antenna to perform its magic must be resonant at the frequency you want it to be. Resonance is a physical phenomenon in many things. It's easier to understand it with sound waves. When you hit resonance the energy spikes and you will see some serious activity. A famous one is getting glassware to resonate which causes it to shatter or hitting 88 MPH and traveling in time.

If you get the antenna to resonate correctly you create an EM field right around the antenna (called literally the near field) but for the EM wave to propagate, which means to spread things have to be just right into the cleverly named far field. We can understand propagation and damping again with audio waves. You might get a speaker to resonate and make sound right in front of it but if you put it in an environment with pillows the sound can't propagate very far.

For propagation the antenna itself is using the "ground" reference in this case as a counterpoise as a stand in for the real ground (Earth). Some antennas and radios must see real Earth to work right. Some don't by design. This gets into the various mode of propagation and where you're trying to communication, e.g. do you want a ground wave, sky wave, to scatter in the atmosphere, to reflect (bounce), etc. But in this case we're just concerned with the direct wave propagation.

Counterpoise is a fancy word but is essentially acting like a phantom part of the antenna. It's not imaginary so much as conceptual, although imaginary is itself a fine description because the situation is complex. But not complex in a conceptual way but in a real and imaginary mathematical way. Without imaginary numbers EM fields would be even more difficult to understand.

None-the-less, the reason for a counterpoise is that an antenna is not an exception to every circuit needing a return (or reference). The most basic antenna is a 1/2λ dipole, which has both sides and is self balanced, no need for Earth or artificial counterpoise to radiate. It was discovered very early that if you take one leg of a 1/2λ dipole (called a 1/4λ monopole) and put it very close to Earth (but not touching) the antenna still works. Then if you want to raise the antenna off the real ground by using something conductive you can trick the antenna into thinking it's over Earth. This can be sheet metal or lengths of wire (called radials) or even your truck body when your radio is using it as reference.

So that's where we're at with vehicle antennas. The basic 1/2λ dipole or 1/4λ monopole with counterpoise will create a mostly spherical pattern with energy almost uniform in all directions.

It was then figured out that various critical lengths of antenna would propagate energy with different patterns. If you use a 5/8λ antenna the pattern isn't uniform but flattened. Think of various antenna lengths like going from a bare light bulb illuminating in all directions to using mirrors and lenses to focus the light. A 5/8λ antenna is like putting a mirror over the bulb so no light goes up and it'll seem a little brighter around the bulb. Other antennas, like a Yagi or a dish focus the RF even more, very much like using mirrors and lenses. All of this is good if you want to reach out further in the horizon and don't care about vertical, which is typically the case. But the problem is a 5/8λ doesn't present 50Ω to the radio so the circuit would be incomplete. We put a small circuit at the base of the antenna to "match" to overcome this.

The antenna still needs a counterpoise to stand-in for ground. There is a special case antenna, a 1/2λ end fed monopole that is self contained. It does not need Earth or an artificial counterpoise to radiate. The problem is it needs to be correctly matched to 50Ω since it actually would normally be very high impedance.

When you see "no ground plane" antennas that's what they mean, they do not need a counterpoise to work. These are the only antennas that strictly speaking do not need the antenna mount to be well "grounded" to the vehicle to use it as a counterpoise. As long as they have a good connection to both the center and outer conductors of the coax they'll work. A 1/2λ is the only one for which that is true, though.

Any other antenna will need something to work against. If you don't provide one the RF will do its best to find one, the coax shield itself is one common one. This is a problem because if the coax shield is part of the antenna that means it will be radiating RF along it, which means it gets into vehicle wiring, in the radio, into you.

Positioning the antenna on the vehicle does determine how well it's going to work. You want the antenna to be clear of things might cause interference with it radiating. Dead center of the roof is far and away the best choice for VHF and UHF antennas. If you can't do that you want the most amount of mast above metal, especially metal that is conductive to the vehicle chassis. Metal that is insulated (perhaps due to rubber isolators, plastic screws or rust) may be bad or might be indifferent. It very, very rarely is beneficial to have your antenna close to anything, especially metal, though.

 

[nwoods]

.... or hitting 88 MPH and traveling in time.

Ha! I see what you did there.
Thanks for the really well written tutorial. I'm gonna walk away from this thinking I was pretty much right, but for all the wrong reasons

 

[Hillbilly Heaven]

Yeah don't confuse Electrical and RF Ground.

 

[Billoftt]

Yeah don't confuse Electrical and RF Ground.

And then earth ground...

At any rate, I am thinking that ExPo needs to put Dave on the payroll as a contributing editor. I have benefited way more from reading his postings over the editors glowing reviews of every fly-by-night company’s overpriced crap.


Sent by electrons or some crap like that.

 

[SHIfTHEAD]

We don't do any favors by using terms indiscriminately, such as "ground" in this case. Ground, as in the Earth, plays a role in the radio arts but here it's best to use it carefully.

You need circuit returns, which is what the "ground" means for the electrical feed line (connectors and coax) and antenna. Ground is understood to be the vehicle chassis and that's significant because the radio uses the vehicle as a power and RF reference.

The circuit in the radio that is imposing energy on the coax needs the circuit to be complete all the way to the antenna with a consistent impedance of 50Ω. If anywhere along the path up to and including the antenna itself is anything other than 50Ω the RF energy will be stymied. We see this measured in the reflection of EM waves back from what we call a discontinuity.

The radio connector has a center and outer contact that match the coax center and shield conductors. So far the circuit has both signal and return for the circuit. When it hits the antenna it might see various things such as a SO239 like the radio, an NMO, a 3/8" stud, two terminals. In most vehicles the antenna itself is only half of the true antenna so for the circuit to be complete the return side of the circuit needs a good path to the vehicle chassis.

If the whole electric circuit is done properly you may successfully energize the antenna such that it may be successful in radiating an EM wave into space.

For an antenna to perform its magic must be resonant at the frequency you want it to be. Resonance is a physical phenomenon in many things. It's easier to understand it with sound waves. When you hit resonance the energy spikes and you will see some serious activity. A famous one is getting glassware to resonate which causes it to shatter or hitting 88 MPH and traveling in time.

If you get the antenna to resonate correctly you create an EM field right around the antenna (called literally the near field) but for the EM wave to propagate, which means to spread things have to be just right into the cleverly named far field. We can understand propagation and damping again with audio waves. You might get a speaker to resonate and make sound right in front of it but if you put it in an environment with pillows the sound can't propagate very far.

For propagation the antenna itself is using the "ground" reference in this case as a counterpoise as a stand in for the real ground (Earth). Some antennas and radios must see real Earth to work right. Some don't by design. This gets into the various mode of propagation and where you're trying to communication, e.g. do you want a ground wave, sky wave, to scatter in the atmosphere, to reflect (bounce), etc. But in this case we're just concerned with the direct wave propagation.

Counterpoise is a fancy word but is essentially acting like a phantom part of the antenna. It's not imaginary so much as conceptual, although imaginary is itself a fine description because the situation is complex. But not complex in a conceptual way but in a real and imaginary mathematical way. Without imaginary numbers EM fields would be even more difficult to understand.

None-the-less, the reason for a counterpoise is that an antenna is not an exception to every circuit needing a return (or reference). The most basic antenna is a 1/2λ dipole, which has both sides and is self balanced, no need for Earth or artificial counterpoise to radiate. It was discovered very early that if you take one leg of a 1/2λ dipole (called a 1/4λ monopole) and put it very close to Earth (but not touching) the antenna still works. Then if you want to raise the antenna off the real ground by using something conductive you can trick the antenna into thinking it's over Earth. This can be sheet metal or lengths of wire (called radials) or even your truck body when your radio is using it as reference.

So that's where we're at with vehicle antennas. The basic 1/2λ dipole or 1/4λ monopole with counterpoise will create a mostly spherical pattern with energy almost uniform in all directions.

It was then figured out that various critical lengths of antenna would propagate energy with different patterns. If you use a 5/8λ antenna the pattern isn't uniform but flattened. Think of various antenna lengths like going from a bare light bulb illuminating in all directions to using mirrors and lenses to focus the light. A 5/8λ antenna is like putting a mirror over the bulb so no light goes up and it'll seem a little brighter around the bulb. Other antennas, like a Yagi or a dish focus the RF even more, very much like using mirrors and lenses. All of this is good if you want to reach out further in the horizon and don't care about vertical, which is typically the case. But the problem is a 5/8λ doesn't present 50Ω to the radio so the circuit would be incomplete. We put a small circuit at the base of the antenna to "match" to overcome this.

The antenna still needs a counterpoise to stand-in for ground. There is a special case antenna, a 1/2λ end fed monopole that is self contained. It does not need Earth or an artificial counterpoise to radiate. The problem is it needs to be correctly matched to 50Ω since it actually would normally be very high impedance.

When you see "no ground plane" antennas that's what they mean, they do not need a counterpoise to work. These are the only antennas that strictly speaking do not need the antenna mount to be well "grounded" to the vehicle to use it as a counterpoise. As long as they have a good connection to both the center and outer conductors of the coax they'll work. A 1/2λ is the only one for which that is true, though.

Any other antenna will need something to work against. If you don't provide one the RF will do its best to find one, the coax shield itself is one common one. This is a problem because if the coax shield is part of the antenna that means it will be radiating RF along it, which means it gets into vehicle wiring, in the radio, into you.

Positioning the antenna on the vehicle does determine how well it's going to work. You want the antenna to be clear of things might cause interference with it radiating. Dead center of the roof is far and away the best choice for VHF and UHF antennas. If you can't do that you want the most amount of mast above metal, especially metal that is conductive to the vehicle chassis. Metal that is insulated (perhaps due to rubber isolators, plastic screws or rust) may be bad or might be indifferent. It very, very rarely is beneficial to have your antenna close to anything, especially metal, though.

I haven't said much on this forum, but this old thread reply deserves a hearty Thank You for being so well written and informative!