Mobile GMRS Antenna

[N4SRN]

I put my 2m/70cm Dual Band antenna on my NMO roof rack mount and tried to TX from a 5W GMRS HT as I approached my home, with a Uniden SDS200 scanner RXing on a desktop discone inside a 2nd story window. The only TX received was 300yd away - shouting distance.

Wow - that was bad.

Was it more the wrong TX antenna or a poor RX system? Yeah, a roof rack mount is not a good thing…

BRET. N4SRN/WRFX595

 

[mmckenna]

Depending on the antenna, the frequencies used by GMRS may be too far out of the usable bandwidth of the antenna, but I'd still expect it to do better than 300 yards.

Poor ground plane from the mount would certainly add to it.

Could be an issue with the scanner antenna inside the home. Might work fine for higher power public safety systems, but would probably not work well for 5 watts with a less than ideal antenna system.

 

[N4SRN]

Turns out I have a Larsen NMO 150/450/785 Triband Antenna with Spring I’d forgotten about - maybe I should give that a try! I also have an Ed Fong GMRS rollup I can hang outside to up my RX.

The stuff that’s on the back shelf comes in handy sometimes!

 

[mmckenna]

Here's the full sweep of that antenna:


Here's just the UHF band:

 

[jeepsandradios]

I run the Larsen Tri band on my work truck and Jeep. It works well. Better than a 1/4 wave but not a huge simplex performer. I can talk to home from about 10 miles away but have a DB404 on the roof of the house. You mentioned antenna on vehicle but not whats on the scanner.

 

[N4SRN]

Here's the full sweep of that antenna:


Here's just the UHF band:

Thanks - that Triband is pretty good for GMRS and 2m/70cm Ham bands. My Dualband is a 62” Comet Super Beam fold-over but the 5W TX and roof rack mount are limiting.

Reviewing my scanner recordings, I found a good test record from 1/2mi away, so better than 300yd on 5W. The next signal 1.3mi out was a no-go…a lot of intervening forest.

I’m just gonna have to bite the bullet and install a roof NMO mount and put my KWD TM-D710G in my new car (2022 Hyundai Tucson n-line). I had a lift gate mount on my 2015 Subaru Forester (as it had a sunroof) but ruined the automatic lift while bonding during the install...some small wire, somewhere. I drilled my own NMO mount on a 2009 Subaru Forester buy felt iffy wrt cable routing and the airbags. I don’t want to even try it on the 2022 Hyundai!

I found a vehicle installer ~20mi away that said they could install an NMO mount - I assume they have access to vehicle schematics and can do so properly. I might as well let them connect to the vehicle power for me too - the more modern the car, the more tricky the connection. I have a battery box and alternator charging switch to run off the car battery when the alternator is running and the battery box when off.

I might just have to swap antennas when using different services for acceptable TX with my group - Ham, GMRS, FRS and MURS are just not one antenna fits all!

 

[N4SRN]

I run the Larsen Tri band on my work truck and Jeep. It works well. Better than a 1/4 wave but not a huge simplex performer. I can talk to home from about 10 miles away but have a DB404 on the roof of the house. You mentioned antenna on vehicle but not whats on the scanner.

The scanner is using a desktop discone inside by a window - not the best by far! My wife won’t let me put another antenna outside so I’m thinking an OmniX in the attic by a window - no metal/foil in the roof or walls and a single metal light conduit for the walk up attic.

I have a Diamond X50a above the roofline for VHF/UHF to a KWD TM-D10G

 

[N4SRN]

Yeah, the Larsen Triband is much better - range tested at 1.1mi vs 1/2mi on the 2m/70cm Dualband.

 

[mmckenna]

I think if you hooked up your scanner to the X50 and did your drive test again, you'd see a significant improvement. Even with the X50 being used outside it's intended band.