Yet another GMRS radio question.

[Keith1138]

I'm trying to dial in my GMRS set up in my jeep and truck. Both have a 15watt midland GMRS radio paired with 6DB gain antenna. Both were considered "pretunned". I was only able to talk about 1.5 miles away. The jeep was sitting in the driveway of my house in a neighborhood. The neighborhood does sit down in a bowl. The line of "sight" was disrupted by two decent hills, trees, and houses. I feel like with these set ups my range should be greater than 1.5 miles even with the obstructions.

Both antenna mounts are not extremely ideal but are mounted with specific intentions. The jeeps is mounted to be protected. The trucks is mounted to be discrete but both still use the roof line as a grounding plane.

I ordered a swr meter to check that on each setup. Any other things to check or considered?

 

[BigClay]

I am no help except I know I got on a repeater channel once and may or may not have accidentally used a cuss word on the trail and some dude 20 miles away chastised me for it

 

[CasterTroy]

"Whoever used the 4 letter word on the air...you just broadcast that to all of Knoxville and that will NOT be tolerated"

 

[StretchASU]

I am no help except I know I got on a repeater channel once and may or may not have accidentally used a cuss word on the trail and some dude 20 miles away chastised me for it

It’s amazing how many boomer burt gummer wannabe basement gnomes are on those channels. I got chastised for not properly broadcasting my license number callsign whatever the hell they call it when chatting around the farm one day. I was on top of the Mtn with essentially uninterrupted line of sight 270* around me and called back to my FIL 1/2 a mile away in the same pasture just to let him know I was coming back with fuel for to top off for the morning. I barely had my finger off the button when we got lit up by someone for being on the channel unannounced.

 

[JSJJ388]

Neither of those antenna setups are going to work very good. Both are very directional, and don't make effective use of the ground plane. You want most of your antenna above the ground plane.

Were you pointing towards what you wanted to talk to? If not, I'd say a few miles is about what I'd expect. 15 watts isn't much juice, especially in a bowl and with LOS obstructions.

 

[Keith1138]

Neither of those antenna setups are going to work very good. Both are very directional, and don't make effective use of the ground plane. You want most of your antenna above the ground plane.

Were you pointing towards what you wanted to talk to? If not, I'd say a few miles is about what I'd expect. 15 watts isn't much juice, especially in a bowl and with LOS obstructions.

Okay. The purpose of these radios is to talk vehicle to vehicle so im hoping to get a few miles. The range was the exact same when I was heading away from the house and towards the house. I had some one use the jeep radio while I drove away in the truck. Then I turned around and headed back towards it. How does the antenna determine ground plan? The jeep one is mounted right above the hood and the truck has the tool box right below it. I'm currently interested in all this stuff.

 

[shawn]

Put the antenna on the roof if you want the best propagation. Don't put it alongside the cab/a-pillar/etc, where the signal is blocked/redirected by the metal of the vehicle.

GMRS is UHF and will bounce around a little (mostly off buildings), but it's still essentially line of sight.

 

[JSJJ388]

Okay. The purpose of these radios is to talk vehicle to vehicle so im hoping to get a few miles. The range was the exact same when I was heading away from the house and towards the house. I had some one use the jeep radio while I drove away in the truck. Then I turned around and headed back towards it. How does the antenna determine ground plan? The jeep one is mounted right above the hood and the truck has the tool box right below it. I'm currently interested in all this stuff.

Since you're interested, I'm happy to dive off in the rabbit hole lol. So your antenna radiates the signal. What type of antenna (these are verticals using the vehicle body as ground plane), and the ground plane reflects the signal. To get the most out of the setup you need to have the radiating element above the reflecting element completely and have a solid electival connection between the coaxial shield and the ground, and the center and the antenna. These are non directive when set up properly. As you move the radiating element off center of the reflecting element (antenna off center of vehicle) they become more directional.

In both your setups, the radiating element is nowhere near center of the ground plane, and the ground plane is not properly bonded to the coax. This makes the system really inefficient.


Hope I explained that well, without sounding like an arse. It's a lot easier to show vs tell. If this stuff interests you, I'd really encourage you to get your amateur radio license. The study app and tests will really help you learn this stuff and there's a whole world of science revolving around building antennas. My second favorite part if the hobby!

 

[Keith1138]

Put the antenna on the roof if you want the best propagation. Don't put it alongside the cab/a-pillar/etc, where the signal is blocked/redirected by the metal of the vehicle.

GMRS is UHF and will bounce around a little (mostly off buildings), but it's still essentially line of sight.

Yes best situation for range would be for the antenna to be mounted in the center of the roof. A 32 inch whip antenna would live a hard life mounted on the roof of my cherokee actually wheeling around the east coast. I'm trying to make my current set up preform the best it can given the mounting locations.

 

[JSJJ388]

Yes best situation for range would be for the antenna to be mounted in the center of the roof. A 32 inch whip antenna would live a hard life mounted on the roof of my cherokee actually wheeling around the east coast. I'm trying to make my current set up preform the best it can given the mounting locations.

Then your best option is a 50 watt rig and as short a run of coax as you can get.

FWIW on my 50 watt yaesu going to a simple mag mount on top of my dakota, I can hit the stone mountain GMRS repeater from union Grove. Roughly 30 miles. A solid ground plane is the biggest factor, but more powah doesn't hurt!

 

[Keith1138]

Since you're interested, I'm happy to dive off in the rabbit hole lol. So your antenna radiates the signal. What type of antenna (these are verticals using the vehicle body as ground plane), and the ground plane reflects the signal. To get the most out of the setup you need to have the radiating element above the reflecting element completely and have a solid electival connection between the coaxial shield and the ground, and the center and the antenna. These are non directive when set up properly. As you move the radiating element off center of the reflecting element (antenna off center of vehicle) they become more directional.

In both your setups, the radiating element is nowhere near center of the ground plane, and the ground plane is not properly bonded to the coax. This makes the system really inefficient.


Hope I explained that well, without sounding like an arse. It's a lot easier to show vs tell. If this stuff interests you, I'd really encourage you to get your amateur radio license. The study app and tests will really help you learn this stuff and there's a whole world of science revolving around building antennas. My second favorite part if the hobby!

Thanks for the great response!! In the case of the jeep where the coax to mount to antenna has a claw thing that I'm assuming grounds the coax to the mount is touching the bracket welded to the cage. The cage is welded to sliders that are welded the jeep there for everything is grounded to it. So would the cage, hood or roof act as the ground plane since the antenna base sits 4 inches above the hood but the tip of the antenna is 6 inches above the roof? I have a decent understand of how electromagnetic waves work in relation to wave length and frequency along with reflection and refraction. I understand there is essentially a dead spot to the passenger side of the jeep because of the cage and a pillar. Which happened to be the side I was on when I tested the range.

 

[Keith1138]

Then your best option is a 50 watt rig and as short a run of coax as you can get.

FWIW on my 50 watt yaesu going to a simple mag mount on top of my dakota, I can hit the stone mountain GMRS repeater from union Grove. Roughly 30 miles. A solid ground plane is the biggest factor, but more powah doesn't hurt!

I ordered a NanoVNA-H to check my swr and tune as needed to try to push these 15watt as much as possible. If I wanted to hit repeaters and go for true distance I would go with a 50 watt. Is there anything else I need to measure besides swr to tune my current set up?

 

[shawn]

I ordered a NanoVNA-H to check my swr

Probably a waste of time/money with 70cm.

Start by putting the antenna straight up and down and move it away from the cage.

Wattage doesn't matter if your antenna is in a bad location. It's just going to have more power to radiate into your A pillar.

 

[JSJJ388]

Thanks for the great response!! In the case of the jeep where the coax to mount to antenna has a claw thing that I'm assuming grounds the coax to the mount is touching the bracket welded to the cage. The cage is welded to sliders that are welded the jeep there for everything is grounded to it. So would the cage, hood or roof act as the ground plane since the antenna base sits 4 inches above the hood but the tip of the antenna is 6 inches above the roof? I have a decent understand of how electromagnetic waves work in relation to wave length and frequency along with reflection and refraction. I understand there is essentially a dead spot to the passenger side of the jeep because of the cage and a pillar. Which happened to be the side I was on when I tested the range.

Unless you've bonded all the body panels, doors, and hod together, they won't be am effective ground plane without the coax shield being connected. One thing you could do depending on how the antenna connects to the coax is to tie in a wire to the shield side and then connect that to the sheet metal of the hood and or roof. This is what I did for my HF mobile set up using the ATAS-120 screwdriver antenna. Bonded the shield to the truck bed, toolbox, bed, cab, and hood. Furthest contact was Chile while coming through yadkinville on 421 NB, but I regularly talked to Brazil, Canada, and Europe while on the road.

I ordered a NanoVNA-H to check my swr and tune as needed to try to push these 15watt as much as possible. If I wanted to hit repeaters and go for true distance I would go with a 50 watt. Is there anything else I need to measure besides swr to tune my current set up?

A nano vna is a great tool. You could get a setup to test field strength and directivity, but that'd be way overboard for what you're trying to accomplish. If all you want to do is talk to your group on the trail, checking swr and getting it reasonably low will be just fine.

 

[shawn]

Unless you've bonded all the body panels, doors, and hod together, they won't be am effective ground plane without the coax shield being connected. One thing you could do depending on how the antenna connects to the coax is to tie in a wire to the shield side and then connect that to the sheet metal of the hood and or roof. This is what I did for my HF mobile set up using the ATAS-120 screwdriver antenna. Bonded the shield to the truck bed, toolbox, bed, cab, and hood. Furthest contact was Chile while coming through yadkinville on 421 NB, but I regularly talked to Brazil, Canada, and Europe while on the road.



A nano vna is a great tool. You could get a setup to test field strength and directivity, but that'd be way overboard for what you're trying to accomplish. If all you want to do is talk to your group on the trail, checking swr and getting it reasonably low will be just fine.

That glass mount has got to be NGP. Mounted too low, regardless.

 

[shawn]

What antennas are these? Link?

 

[Keith1138]

What antennas are these? Link?

The glass mount is a Tram 1192. The jeep one is from Midland.

 

[shawn]

The glass mount is a Tram 1192. The jeep one is from Midland.

Ok cool. I was hoping to find specs on them that say for sure, but didn't have any luck. My guess is that these are center loaded. If so, the coil in the middle of the whip is where most of the radiation comes from. Imagine the radio waves propagating outward in all directions from that point. If it's mounted below the cab roof, a lot of that radiation is getting absorbed or redirected by the body of the vehicle. IME, antennas mounted on the sides of the truck live short, hard lives before they get scrubbed off by a rock or tree. You can get a NMO mag mount for the roof or (if you're cool with cutting a hole in the roof) use a NMO through-mount. That'll give you a much better propagation pattern, more gain, and the antenna might actually live longer.

 

[JSJJ388]

Honestly, I'd just do like @shawn said and go mag mount. Doing that will mean your antenna and sheet metal won't get damaged when the whip gets hung on something.

 

[No fries]

I've used this one on my tow vehicle with good results up to 15 miles transmission with a midland MTX115. I looked for the one we have on the cherokee but couldn't find it on their site anymore. (Another mag mount) It has been in the center on the roof near the rear hatch for over three years now. It is magnetic and only thing would knock it off would be branches but it has stayed on without damage bouncing up rock while on the revlimimiter without problem.

MicroMobile® MXTA13 2.1dB Replacement Antenna

Upgrade your long range radio antenna with our magnetic base antenna. Enhance your communication capabilities with the MXTA13 2.1DB replacement antenna.

midlandusa.com

 

[shawn]

Oh, and keep in mind that the center of propagation is perpendicular to the antenna, so if you lay the antenna back at an angle, not only is it directing some of the energy up into the sky and down into the ground, but the waves themselves are also turned (incidentally, this is one reason why wifi access points have antennas turned 45* to one another), making reception on the other end less than ideal.

 

[cranbiz]

I have Diamond 770's on all my vehicles. The Diamond is a dual band 6db gain no ground plane antenna and just works. Only the one on my JK is in what would be close to an optimal placement. The Motorhome's is mounted to the front fender and the JT's is mounted to the bed next to the hard top. All of them will talk multiple miles on GMRS on 10W. I use 5W on the trails and it's just fine. Halfway up Potts, in the JK, I can get back to both a 2M repeater in Madison and back to the Fire Dispatch center on 460 MHZ in Wentworth on 50W, approximately 160 miles, and be readable.

When traveling, I can usually talk 3-5 miles on GMRS simplex from the motorhome to Jim Smith behind me in his Gladiator (when we get separated) and my antenna is probably in the worst place in the world to try that.

Personally, I have used Tram antennas and found them lacking. I don't have any experience with the Midland antennas.

 

[Keith1138]

So I checked both antennas swr with the Nano after following the calibration instructions. The truck measured 1.29. The jeep measured 1.26. Both are from the middle of gmrs frequency range. Both antennas swr had a very slight sweep through the frequency range. Since the video I watched showed how to set up to measure the ohms (I think for impedance) i set it up to also measured that. The truck was 60.9 and the jeep was 45.1. After brief research the ideal amount would be 50. Is there a way to get these numbers closer to 50 or is it good enough or doesn't matter?


I know for best performance I should have the antennas higher and away from pillars. I'm just trying to optimize performance the best I can with where they are mounted.

The Truck

The Jeep

 

[JSJJ388]

So I checked both antennas swr with the Nano after following the calibration instructions. The truck measured 1.29. The jeep measured 1.26. Both are from the middle of gmrs frequency range. Both antennas swr had a very slight sweep through the frequency range. Since the video I watched showed how to set up to measure the ohms (I think for impedance) i set it up to also measured that. The truck was 60.9 and the jeep was 45.1. After brief research the ideal amount would be 50. Is there a way to get these numbers closer to 50 or is it good enough or doesn't matter?


I know for best performance I should have the antennas higher and away from pillars. I'm just trying to optimize performance the best I can with where they are mounted.

The Truck
View attachment 418271

The Jeep
View attachment 418275

To adjust the impedence (ohms) you adjust the length of the antenna.

 

[Keith1138]

To adjust the impedence (ohms) you adjust the length of the antenna.

Would I see any improvement by adjusting them to 50? Does lengthening the antenna increase or decrease the ohms?