High SWR on mobile 4x4 install

[erictrex]

Amateur here! Getting ~8 SWR on following setup:

Surecom SW102 meter
Wouxun KG-1000G GMRS radio
EM Wave EM-M11001-195 5 dBi Ground Plane Independent Antenna 440-480
EM Wave EM-M11001-195 NMO Hole Mount Assembly with 17 ft. Low Loss 195 Cable
Mounting: Tube on rear tire carrier of 4x4. Not intentionally grounded since antenna is NGP type
TX test: 5w @ 462.6375 MHz (GMRS CH 4)

Antenna is near objects obviously, but that's the nature of a vehicle install. I'm otherwise testing outside my house. Not sure what I can adjust since the antenna data sheet insists tuning is not necessary for the intended frequency range.

Any suggestions? Thanks!

 

[nokones]

Amateur here! Getting ~8 SWR on following setup:

Surecom SW102 meter
Wouxun KG-1000G GMRS radio
EM Wave EM-M11001-195 5 dBi Ground Plane Independent Antenna 440-480
EM Wave EM-M11001-195 NMO Hole Mount Assembly with 17 ft. Low Loss 195 Cable
Mounting: Tube on rear tire carrier of 4x4. Not intentionally grounded since antenna is NGP type
TX test: 5w @ 462.6375 MHz (GMRS CH 4)

Antenna is near objects obviously, but that's the nature of a vehicle install. I'm otherwise testing outside my house. Not sure what I can adjust since the antenna data sheet insists tuning is not necessary for the intended frequency range.

Any suggestions? Thanks!

The antenna mount should have chassis ground continuity without the coax cable being connected to the radio regardless if you're using a groundplane antenna or not.

Also, you may have one of those itty bitty strands of the braided wire shorting out at the connector. With the antenna removed from the NMO mount, get your multi-meter and check to see if you have continuity between center pin and the outside of the connector. If you do have continuity, it would be best to whack off the connector and reinstall a new connector and constantly checking for shorts during each step of reinstalling the connector.

If you have an antenna analyzer, I would sweep the antenna to verify the center freq resonance of the antenna.

 

[exkalibur]

Are you able to attach a picture of the antenna installation?

 

[erictrex]

After trying the suggestions above, it turns out the antenna wasn't tight enough to make contact at the center conductor! Thought I had it tight already. Adjusted the conductor tab and tightened the connection more and bam - 1.01 VSWR! Can't complain about that.

However, when I switch from any of the 462MHz channels to any of the 467 MHz channels, the SWR jumps to ~2.18. Maybe an unavoidable result of the mounting conditions?

Mounting pics:

 

[mmckenna]

Antenna is near objects obviously, but that's the nature of a vehicle install.

Yes, photos would help.

If the antenna is up against a tailgate or other metal, that may be your issue. Choosing a different mounting location may be required.

Either way, photos or sharing some details about the exact mounting location, model vehicle, or any other pertinent information would be very, very helpful.

 

[prcguy]

I don't see any ground plane to speak of and that will affect tuning and will definitely reduce range. I would expect a reasonable SWR from 462 to 467 but if you tuned it to 462 it could actually be a little lower in freq causing a problem at 467. I would tune it more in the middle like 464.5MHz by cutting 1/4" off at a time to get the match down at 467 without letting it raise too high at 462.

This is where an antenna analyzer is better than an SWR meter where you can actually find where the antenna is tuned and also see what the SWR is across 5MHz of band width without having to cut the whip. If the SWR is good across 5MHz but its just tuned too low you will know it will be ok by cutting more off and centering it between 462 and 467. You can't do that with an SWR meter unless you can program the radio and transmit out of band which is not a good idea.

 

[mmckenna]

I don't see any ground plane to speak of and that will affect tuning and will definitely reduce range. I would expect a reasonable SWR from 462 to 467 but if you tuned it to 462 it could actually be a little lower in freq causing a problem at 467. I would tune it more in the middle like cut 1/4" off at a time to get the match down at 467 without letting it raise too high at 462.

From his post, I think he has this antenna:

EM Wave EMFLX-M10007-GPI UHF 440-480 MHz Tunable Mobile Antenna - No Ground Plane Required - e/m-Flex® Spring

EM Wave EMFLX-M10007-GPI UHF 440-480 MHz Tunable Mobile Antenna - No Ground Plane Required - e/m-Flex® Spring

theantennafarm.com

 

[mmckenna]

After trying the suggestions above, it turns out the antenna wasn't tight enough to make contact at the center conductor! Thought I had it tight already. Adjusted the conductor tab and tightened the connection more and bam - 1.01 VSWR! Can't complain about that.

However, when I switch from any of the 462MHz channels to any of the 467 MHz channels, the SWR jumps to ~2.18. Maybe an unavoidable result of the mounting conditions?

Might be. Having all that metal directly parallel to the antenna whip is going to knock it out of tune. I'd find somewhere else to mount it.
That location is going to give you problems.

Low SWR is good, but it's not the only concern….

 

[erictrex]

From his post, I think he has this antenna:

EM Wave EMFLX-M10007-GPI UHF 440-480 MHz Tunable Mobile Antenna - No Ground Plane Required - e/m-Flex® Spring

EM Wave EMFLX-M10007-GPI UHF 440-480 MHz Tunable Mobile Antenna - No Ground Plane Required - e/m-Flex® Spring

theantennafarm.com

Yes, I have the EMFLX-M10007-GPI. Typo in original post that I can't edit.

 

[erictrex]

Might be. Having all that metal directly parallel to the antenna whip is going to knock it out of tune. I'd find somewhere else to mount it.
That location is going to give you problems.

Low SWR is good, but it's not the only concern….

Yeah the rear was a compromise. There's no metal roof and I couldn't pull into the garage with an antenna up there if it was. The only other good (for tx/rx) options I see are the front wing/fender (several issues there though), or mounted off the front bull bar (vulnerable and often in the way). I'll be consider mounting options a bit more though. Thanks

 

[mmckenna]

You have the option of going with a smaller antenna.

You can get 1/2 wave "no ground plane" antennas that are 12" or so tall. One with a spring on a good mount will take all the abuse you can throw at it. I know, I run a 1/2 wave VHF whip on the top of the roll cage on a Polaris Ranger UTV, and it's hit some low tree branches at 30+ MPH.

 

[mmckenna]

Here 'ya go:

16" 1/2 wave (no ground plane required) UHF antenna. EM Wave EM-M10003-GPI UHF 420-470 MHz Tunable 3dB Mobile Antenna- Steel Spring Base - No Ground Plane Required

But see if you can find a way to mount it up on top. That'll help the performance.

I run the VHF version of this antenna on the UTV:

Laird TE Connectivity B4502NS UHF 450-470 MHz Mobile Antenna - No Ground Plane Required - Spring Base

Laird TE Connectivity B4502NS UHF 450-470 MHz Mobile Antenna - No Ground Plane Required - Spring Base

theantennafarm.com

It's been up on top of the roll cage for almost 15 years and hit a lot of tree branches, to the point that the whip has a permanent kink in it. Antenna still sweeps just fine and performs like new.

 

[nokones]

Here are a couple options for you, a Larsen Glass-mount antenna. You'll be totally surprised on how well this antenna performs. I am able to hit several repeaters 65-70 miles away and simplex traffic 15-20 miles away. The VSWRs are 1.07:1 on 462 Megs and 1.5:1 on 467 Megs.

The TE Connectivity/Laird/Antenex/Antenna Specialist antenna side-mounted near the cowl on a Rugged Radios Mounting bracket with a TE Connectivity 3/8" hole NMO Mount cable, also works very well with a TE Connectivity B1442N Non-Groundplane VHF antenna also preforms very well. As for the VSWRs, I am getting 1.2:1 on 151 Megs and 1.5:1 on 154 Megs and 1.7:1 on 158 Megs. Yes, I could snip or two more off to bring down the 158, but most of my VHF stuff is 151 & 154 Megs, so it is good enough for old people retired amateur work and I don't mean or claim any connection with the Amateur Radio Service.

With the side-mount antenna, I am able to communicate with a VHF repeater 30-35 miles away with a large hill in between the two mounts. The repeater is located on a building with 4 levels.

I am using these two options on my 23 Wrangler Rubi 2 Dr.

 

[erictrex]

Appreciate the suggestions guys - good food for thought. The Defender's windshield is surrounded by a roll cage (like pic below) so that also limits options. I could probably fit a stubby antenna on the top bar and still squeak into the garage but I'd have to weigh the difference in gain between any stubby and this nice EM half-wave I've got. Considering mounting it to a custom bracket between the bonnet (hood) and wing (fender) - that would bring its height to a reasonable level, move it away from perpendicular metal surfaces, and be inward enough to avoid some brush.

 

[merlin]

I wouldn't expect much performance with this mounting setup. The very base of the antenna has a tuning coil there and should be clear of any metal, 3 inches or more. Usually a tire, except the rim won't be an issue unless the tire is steel belted, then you are going to have problems.
Any reason you cant drill a 3/4 hole in that flange (above the kolpin logo) mount the antenna there.
The roll bars will introduce some directional characteristics, but performance should improve.
And yes, run a ground strap, say from a rollbar bolt to the flange.