GMRS Antenna Options
- Thread starter Beowulf
- Start date
DaveInDenver
Middle Income Semi-Redneck
Do you need gain? Either way I doubt there'll be much selection for SO239 bases in single band antennas since Laird and Larsen only use NMO.
You might be able to adapt a ham dual band 2/70 to work. Comet, Diamond and Nagoya make several PL259 base antennas that you could probably cut or tune for GMRS. That would probably make them dedicated GMRS and no longer dual band ham, though.
Or you could make your own 1/4λ, it wouldn't be difficult to use a PL259 and 7" of brass rod. Larsen makes a model PQ that is a field tunable handheld that is essentially just that.
You might be able to adapt a ham dual band 2/70 to work. Comet, Diamond and Nagoya make several PL259 base antennas that you could probably cut or tune for GMRS. That would probably make them dedicated GMRS and no longer dual band ham, though.
Or you could make your own 1/4λ, it wouldn't be difficult to use a PL259 and 7" of brass rod. Larsen makes a model PQ that is a field tunable handheld that is essentially just that.
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You want an NMO mount because it’s waterproof and a constant impedance. Further, about 400 MHZ the UHF connectors start having issues with loss. That is why radios should have N connectors up that high.
Look at Larsen antenna for a good GMRS antenna. They are what the pros use and are in destructible. I’ve also heard good things about Maxrad.
FWIW no ham mobile antenna is broad enough to cover all the GMRS frequencies effectively. However, building a simple quarter wave from broken parts will do fantastic for 99% of users.
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Look at Larsen antenna for a good GMRS antenna. They are what the pros use and are in destructible. I’ve also heard good things about Maxrad.
FWIW no ham mobile antenna is broad enough to cover all the GMRS frequencies effectively. However, building a simple quarter wave from broken parts will do fantastic for 99% of users.
Sent from my iPhone using Tapatalk
DaveInDenver
Middle Income Semi-Redneck
Bandwidth of any antenna is due to physics not because it's ham or commercial or otherwise.
Bandwidth is usually specified over the 2:1 SWR range and typically you're looking at about 6%. So since GMRS centers around 462 and 467 you'd want to tune for halfway between the two, 464.5 MHz and 6% (28 MHz or +/- 14 MHz) will easily cover that.
The better performance of 1.5:1 SWR is usually on the order of 3% bandwidth and even that (+/- 7 MHz for 464.5 MHz) is still easily within most antenna's capability. The most basic 1/4λ whip (like a Laird QWFT) has a specified bandwidth of 20 MHz on UHF and GMRS requires less than 8 MHz to cover.
I'm guessing the FCC didn't assign FRS/GMRS without some thought.
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DaveInDenver
Middle Income Semi-Redneck
You gotta narrow down what you want. Do you already have a mount? Do you want gain or not? Does it need any special features like being super flexible or have a spring?
Midland has some mounts and antennas that would probably be the easiest to pick from.
https://midlandusa.com/product-category/accessories/micromobile-accessories/
The only thing they don't seem to sell are regular through hole NMO mounts, if you're interested in mounting the antenna actually in your roof for example.
PhulesAU
Explorer
Ebay has what you seek.
While that is true don’t buy cheap. If you buy cheap expect issues. It’s not that pricey to buy a quality NMO
mount from Larsen, Laird or another major commercial dealer.
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PhulesAU
Explorer
Too True, But will allow you to find part numbers alot easier than the company websites in many cases.
https://www.ebay.com/usr/antenna2-waydirect
https://www.ebay.com/usr/texxcomm
I've had good luck with these 2. especially finding new old stock in or close to the bands I want, just a kittle trim and tune!!
https://www.ebay.com/usr/antenna2-waydirect
https://www.ebay.com/usr/texxcomm
I've had good luck with these 2. especially finding new old stock in or close to the bands I want, just a kittle trim and tune!!
sonoronos
Usually broken down on the side of the road
One thing that I have noticed is that off-the-shelf "GMRS / FRS" antennas aren't quite as easy to find as HAM or commercial VHF antennas.
I'm not sure why this is the case, but my guess is that this is because the acronyms GMRS and FRS were long associated with consumer handhelds (?) until some time recently when GMRS mobile radios started becoming a thing.
In the US, GMRS/FRS freqs now co-exist in the realm of what I've known in the last 15 years as the LMR (Land Mobile Radio) service. This is because USG and public safety are the main users of this part of the spectrum. (For example, if you scan the entire spectrum of bandwidth from around 30Mhz to 900Mhz, you'll find encrypted government comms popping up everywhere, especially in the VHF and UHF bands.)
This is why googling "LMR antenna" returns a ton more results than googling "GMRS antenna" - and there are a LOT of LMR antennas out there.
I'm not sure why this is the case, but my guess is that this is because the acronyms GMRS and FRS were long associated with consumer handhelds (?) until some time recently when GMRS mobile radios started becoming a thing.
In the US, GMRS/FRS freqs now co-exist in the realm of what I've known in the last 15 years as the LMR (Land Mobile Radio) service. This is because USG and public safety are the main users of this part of the spectrum. (For example, if you scan the entire spectrum of bandwidth from around 30Mhz to 900Mhz, you'll find encrypted government comms popping up everywhere, especially in the VHF and UHF bands.)
This is why googling "LMR antenna" returns a ton more results than googling "GMRS antenna" - and there are a LOT of LMR antennas out there.
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DaveInDenver
Middle Income Semi-Redneck
You choose how much gain you would like with the understanding that it's a compromise. As you go up in antenna gain the antenna becomes more directional. That means that more gain equals less uniform pattern.
When talking about whip antennas on vehicle this generally means as gain increases the horizontal strengthens (think of it as "focusing" the energy like a lens focuses light) but the antenna radiates less energy vertically.
The baseline 1/4λ pattern is basically like a dome over you, no particular direction or elevation is significantly better than another. As gain of a whip increase the pattern flattens horizontally, as if you put a mirror over the antenna and the energy is focused towards the horizon.
However, the technical specifics aside, with your bracket location you are probably more concerned with finding one that works well without a good ground plane under it. Different length antennas work differently with respect to the what the radio sees electrically and how it reacts with its environment. Some need sheet metal under them to work well (1/4λ) but others don't to the same extent.
I would suggest you look for a 1/2λ (half wavelength) antenna. That will be most effective at radiating energy efficiently. It will have some stated gain but the actual value of it isn't important. The key is it doesn't need any sheet metal under it to work fine.
When talking about whip antennas on vehicle this generally means as gain increases the horizontal strengthens (think of it as "focusing" the energy like a lens focuses light) but the antenna radiates less energy vertically.
The baseline 1/4λ pattern is basically like a dome over you, no particular direction or elevation is significantly better than another. As gain of a whip increase the pattern flattens horizontally, as if you put a mirror over the antenna and the energy is focused towards the horizon.
However, the technical specifics aside, with your bracket location you are probably more concerned with finding one that works well without a good ground plane under it. Different length antennas work differently with respect to the what the radio sees electrically and how it reacts with its environment. Some need sheet metal under them to work well (1/4λ) but others don't to the same extent.
I would suggest you look for a 1/2λ (half wavelength) antenna. That will be most effective at radiating energy efficiently. It will have some stated gain but the actual value of it isn't important. The key is it doesn't need any sheet metal under it to work fine.
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Billoftt
Active member
Correct me if I am wrong, but wouldn't 5/8 over 5/8 wave or 5/8 over 1/2 wave collinear antannas work decent without ground planes?
Also, I have an antenna that is 3/4 on UHF and I sweat that thing talks to clouds.
DaveInDenver
Middle Income Semi-Redneck
Collinear arrays are a different animal. Answer is not always but maybe yes. Assuming it's actually collinear elements and not marketing speaking for an elevated feed point, might mean a counterpoise (e.g. plane or having radials) is unnecessary to achieve a suitable impedance and useful radiating pattern, but not universally. It depends.
It's more complex than just trying to compare it to taking two fundamentals and producing a third frequency like you might be familiar with in audio. There's usually still only one active element and the other is passive and phased, so what the radio sees and the resulting radiated pattern isn't simple to explain. I guess it could be said it's like the sound you hear when low frequency bass finds a sympathetic thing like your car window and you hear a buzz. Strictly speaking the audio amp sees a load from the speaker that is a complex function of the speaker itself and all the stuff around it pushing back. If you open the buzzing window the amp will technically see a different load (might be lower or higher, but will be different regardless).
A stacked 5/8λ over 5/8λ doesn't mean it looks like a 1/4λ with a perfect return to the radio electrically and radiates like 5/4λ but also won't look exactly like the single 5/8λ you're actually feeding either. It's some complex combination of everything, so the easiest way to say it is you have to follow what the manufacturer recommends. If they say it's ground plane indifferent, then it is.
That's the uniqueness about 2m and 70cm ham, a plain old 1/4λ whip on 2m is very close to a 3/4λ whip on part of the 70cm band. In fact it's close enough that it can be run that way without damaging your radio usually. You notice in the pattern chart above the pattern is still useful, although there's a significant null right where you probably see repeaters.