Installing NMO thru roof mount for GMRS. Looking to install with higher quality coax for less loss. Does anyone know of a NMO mount that will accept larger diameter coax than the RG58? Cable I'd like to use is M&P Hyperflex 5 (.212). Thanks in advance?
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Low loss coax for GMRS
- Thread starter joelr1957
- Start date
There's a couple of options...
But, before you go through all that, consider the cost/benefit.
As you know, coaxial losses go up as the frequency goes up. While all coax has some loss, that amount is actually pretty low. I'm running a lot of 800MHz radios at work. Higher frequency, more loss, but I still run RG-58. The difference between the different grades of cable when only looking at 10-15 feet is really, really small. As in not likely noticeable unless you have really good test equipment. Even at 800MHz, I have no issues with 10-15 runs of cable in vehicles.
You also need to consider cable routing. Higher grade/larger cables get to be harder to run in a vehicle. Not that it cannot be done, it's just that it is additional work. In a commercial environment, installing in a bunch of vehicles, that extra work adds up. For your one vehicle, maybe not a challenge.
You can get NMO mounts with pre-installed Times Microwave LMR-200 easily:
theantennafarm.com
If you really want to roll your own, you can buy just the NMO mounts and install the cable yourself:
theantennafarm.com
But, before you go through all that, consider the cost/benefit.
As you know, coaxial losses go up as the frequency goes up. While all coax has some loss, that amount is actually pretty low. I'm running a lot of 800MHz radios at work. Higher frequency, more loss, but I still run RG-58. The difference between the different grades of cable when only looking at 10-15 feet is really, really small. As in not likely noticeable unless you have really good test equipment. Even at 800MHz, I have no issues with 10-15 runs of cable in vehicles.
You also need to consider cable routing. Higher grade/larger cables get to be harder to run in a vehicle. Not that it cannot be done, it's just that it is additional work. In a commercial environment, installing in a bunch of vehicles, that extra work adds up. For your one vehicle, maybe not a challenge.
You can get NMO mounts with pre-installed Times Microwave LMR-200 easily:
0-6000 MHz, 3/4" Permanent Hole Mount 17' LMR-200. For standard vehicle roof mount antenna installation.
0-6000 MHz, 3/4" Permanent Hole Mount 17' LMR-200. For standard vehicle roof mount antenna installation.
theantennafarm.com
If you really want to roll your own, you can buy just the NMO mounts and install the cable yourself:
Standard NMO Mount Hardware - NMO Hardware Only | The Antenna Farm
theantennafarm.com
Thank You for your reply and the links. I understand the loss is minimal, but I really like my M&P cabling, have it on 2 base antennas. If I decide to "roll my own", lol, do you think cable w/.212 diameter would work w/standard nmo mount? Have A Good One!
K6GBW
Member
For a vehicle it would be better to get a better quality mount with coax that uses a tough dielectric. I use the Larson NMO mounts because they are well made and the coax is super tough. The difference in loss for 10-15 feet won't make any difference, but the coax getting pinched or damaged will.
prcguy
Member
You can get an NMO mount with female N connector on the backside then use a right angle adapter and M&P Hyperflex 13 .500“ if you wish. However I prefer doing this and running 7/8“ Heliax for my GMRS mobile installs.
I went down this rabbit hole. I have a Jeep Gladiator in which I have installed a CB (HF) and a VHF/UHF that I use on public safety frequencies (and maybe, occasionally, though very seldomly, GMRS). Both antennas are NMO mounts.
Initially I used RG58 cable for both antennas (a Laird C27 and a Laird CB150/450). After reading random articles on the web (none of which were on this forum which I found later in my education) I decided to try RG8X on both antennas. One of the biggest problems I ran into was lacing the thicker, stiffer coax through the vehicle and keeping it within the bend specifications. Finally, I replaced the RG8X with RG58A/U. RG58A/U is thinner and much more flexible due to the smaller, stranded core.
Across all three installations I saw no difference in SWR or transmitted power (as measure by a McBazel SF-103). The lesson I have taken away from my experience is that I will default to RG58A/U for vehicle installs going forward.
For the record, I am a hobby guy who is definitely learning as I go and by no means any kind of expert. There are a number of guys in this forum that have forgotten more than I know about RF in general and antenna systems specifically. This is just my own rather expensive lesson. Your mileage will probably vary.
And thanks to the folks here who have contributed to my education.
Initially I used RG58 cable for both antennas (a Laird C27 and a Laird CB150/450). After reading random articles on the web (none of which were on this forum which I found later in my education) I decided to try RG8X on both antennas. One of the biggest problems I ran into was lacing the thicker, stiffer coax through the vehicle and keeping it within the bend specifications. Finally, I replaced the RG8X with RG58A/U. RG58A/U is thinner and much more flexible due to the smaller, stranded core.
Across all three installations I saw no difference in SWR or transmitted power (as measure by a McBazel SF-103). The lesson I have taken away from my experience is that I will default to RG58A/U for vehicle installs going forward.
For the record, I am a hobby guy who is definitely learning as I go and by no means any kind of expert. There are a number of guys in this forum that have forgotten more than I know about RF in general and antenna systems specifically. This is just my own rather expensive lesson. Your mileage will probably vary.
And thanks to the folks here who have contributed to my education.
Where did you measure the power at the radio or at the antenna? There are adapters for NMO to N so you can measure at the antenna through a meter and into a load. That will tell you (within the limits of the meter accuracy) what the loss is between the radio and the antenna.
You can probably make it work. The basic NMO mounts are pretty easy to work with.
Your choice, I just think the amount of work it is going to take is way more than the slight benefit. But if it's what you want, that's what you should do.
Years ago I accidentally bought a mount with LMR-200 (might have been 240). It was a real pain to run, and there was not any noticeable difference between the RG-58 cables. It was enough of a pain, that I've successfully remembered to not do it again.
Guys with far more knowledge and experience than me with far better equipment than I have have verified that in a vehicle install involving 10 to 15 feet of coax, the difference in radiated power is nominal and insignificant. The improvement in radiated power would need to be readily noticeable before I would be interested in trying to run RG8X again. Bragging rights alone are not worth it.
The SF-103 has its own antenna and measures what makes it into the air.
Frequency counter/field strength meter. It'll tell you how much RF the antenna is radiating.
Other way to test is to use one of these:
I don't know what I would connect it to. Additionally, is it not also possible to measure transmission loss of a particular piece of coax with a nanoVNA? I think I saw a YouTube that purported to explain how.
I suppose one could use the NMO adapter and connect an SWR meter and dummy load to the antenna side of the SWR meter?
If you figure an approximate cable run inside a vehicle from the radio to the NMO mount of around 10 feet, and using a 50 watt mobile, it's only 2-3 watts difference.
On the very fringes of coverage, you might see a very slight benefit. But if your radio system really depends on fractions of a dB to work, then there are bigger issues to deal with. Like the system hasn't been designed well at all.
Considering that switching from a 1/4 wave antenna to a 5/8th's wave antenna will gain you about 3dB, WAY more than the cable loss, there's easier ways to tackle this.
For ham radio use where you may be trying to experiment with super weak signal stuff, like bouncing off the moon, then sure, I get that the 0.2dB difference may be worth it. But for mobile radios, GMRS, Ham, CB, even 800MHz stuff, it's just usually not worth the pain in the arse that goes along with bigger coaxial cable.
But it's a hobby, and it's a good place to play around. Experimenting is fun and part of the game.
Would rg142 be an option? Kinda stiff but great for higher power units.
prcguy
Member
Yes it’s lower loss than RG-58 and will handle a lot of power. Problem is it’s very expensive with US made versions costing $3.50 on up per foot. Over the years I’ve picked up a lot of surplus RG-142 cheap and use it in all my mobile installs.
I thought you used 7/8" Heliax?
One inch coax in a mobile install would be interesting to see. I would not want to be the one to lace it through the vehicle.
prcguy
Member
RG-142 from the radio to the amp, 7/8 Heliax from amp to antenna, you silly mod!
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