Looking for a gmrs hood antenna mount

This guys channel is one of the best I have found regarding coms. https://youtube.com/c/NotaRubiconProductions

Optimal and sufficient is really what it’s about. For trail coms with a GMRS sufficient is fine.

 

He has some good info, I have watched many of his vids over the last couple years. Personally, he's quite the hypocrite, but as far as radio info goes, he seems to be full of very useful info and straightforward reviews.

I don't get why one would buy an antenna designed for use with a ground plane when there are other antenna options that don't require a ground plane at all. Is there some other compromise?

 

Yeah in my research there gmrs specific antenna that don’t require a ground plane. Because I spend a lot of time on the interstate I want to be able to get to the repeaters and then go with a ghost antenna for trail use .. thinking of either attaching to the ditch lights or a separate mount point near the rear lights

 

I have a whip type and it's on a hood hinge mount, it's taken a few whacks with no problems to the antenna or the mount. I wouldn't mind a stubby if it would reach the two repeaters that I usually would need to get to if I had an emergency or other problem, but this antenna is already theoretically pushing it for range so I don't want to lose any. As far as trail comms only, its way overkill.

 

What antenna and mount are you using? What length is it? 33.1”?

 

Laird BB4505 spring base. yes 33". Using the Victory4x4 mount. I had to spot face around the through hole about ".040 deep to relieve for the NMO base so that the o-ring would seat, otherwise it was clamping on a raised ring and not making a seal. I believe this would be the case with any of the hood hinge mounts.

 

Just out of curiosity where you able to get a WRS measurement and would be willing to show a picture of your set up? My Wouxon KG 1000 arrived and now I’m looking for the best location (hood or rear tail light) for reception. I’m looking at the 33” for daily driving and the ghost for off road.. any recommendations or suggestions? Also what grade of coax did you go with? I was thinking of

 

If I had to guess, I would say the hood would be better because it at least has some sort of ground plane in 90*+ of the direction. I wouldn't be surprised if the benefit is negligible, though. I chose the hood because an easier/shorter coax run and because I sometimes cover the antenna mount part of the bed/bed rack with my bike mount tray.

I have not made any SWR measurements because I don't have an analyzer, but I would like to do that at some point. The antenna should be very close to optimized for GMRS freqs per Laird, so I'm not losing sleep over it but eventually I will check and adjust if it can be improved. I need to find a radio club near me and see if some experts can school me on everything I need to know.

I am using some generic RJ58 that came as part of a 90* 3/8" NMO mount. Coax cable is nothing special or particularly difficult to manufacture. I wouldn't spend big $ on super high grade stuff for 50watt radio applications. The quality of the termination and terminal hardware makes a bigger difference. I am sure there are differences between the really nice $$$ RJ58 and the basic $ RJ58, but I doubt it makes any measurable difference in this application. Heck, even coiling or wrapping the cable up doesn't make any difference in TX/RX performance for 50watt GMRS stuff. I do plan to cut the coax and re-terminate it when I have the dash apart this fall, but only to satisfy my OCD about clean routing and such.

First picture is the antenna mount capped for when I am not needing to use the radio. My truck shares daily duty with my old subaru but I didn't want an antenna to be on 24/7 in the weather. Also, my antenna taps my garage opening when I go in/out and my RTT if I park front end in, that can't be great for it over time. The screw on cap is brass (I think) and gasketed so it makes a nice weatherproof cover for the NMO mount.






I had to adjust the bend angle of the hood hinge mount just a few degrees so that the antenna didn't lean forward. I did a test fit of the mount before painting or anything and I just clamped it in a vise and tweaked the antenna hole end just a bit with a huge adjustable wrench. It was really easy. Having a helper to hold the hood while you remove/install the hinge bolts is a good idea, too. If you paint yours, make sure to mask off the area where the NMO mount will contact the bracket so that it's grounded with the NMO mount & antenna. I did that on the underside where the NMO mount "teeth" dig in. That should eliminate any chance of noise from the mount/hood not being grounded at the antenna.

 

Wow! Great info and thank you for taking time to take the pictures and responding.
Semper Fi

 

You bet. Post your config when you get a chance, it will probably help someone else down the road.

 

Absolutely!!!

 

How has it held up pulling in and out of the garage? Since most my repeaters are over 50 miles out, I’m thinking of the 6db gain 33”+ antenna’s for daily and the ghost for trail. The issue is that I don’t leave my truck outside when I’m home (too many theives) so I always keep it garaged and was curious if it will stand up the abuse of going in and out hitting the garage door?

 

I don't leave it on for daily driving because I wouldn't use it, but I don't think it will hurt it unless you back out at 30mph


It's held up on the trail and taken a few good hits from trees so I wouldn't worry.

 

Thank you again.

 

Sorry for the delay!

No difference between Tx and Rx between the mid fender and ditch light positions, easily hit the local repeaters when driving around and weekly on the local club nets.

It's a half wave dipole on 2m so it's designed to work without a ground plane - I'm sure it would Tx a bit better mounted in the center of the hood or roof but we've got a Prinsu and its a daily.. so compromise - it's still getting some benefit from being beside the hood, might be pulling Tx to the passenger side but antenna propagation is a bit of a black art.

I went with the Larsen 270B because it's one of the toughest, functional, highly recommended antennas I could source:
https://www.eham.net/reviews/view-product?id=434

Biggest concern of this mounting is the RF Exposure.
http://hintlink.com/power_density.php
Do your own calculations and understand the risks - I don't run at full 50w and rarely tx so I'm confortable with my set up.

 

I looked into this after reading a warning from Midland that I assume they are required or include with the radio to limit liability, but it seems that for intermittent vehicle use even a 50 watt Tx at 1 meter is far from anything to worry about because while it may be 5-10 times over the density "limit" for a 30 minute exposure, Tx times on a mobile radio are typically only seconds long. Halving the time allows for doubling the energy density and if you carry that math out to a few seconds every couple minutes, it falls way off and far below the FCC guidelines limit. That is my understanding of it anyway, and I would be happy to know that I am mistaken if that is the case.

 

You mean since it’s a half wave on 2m it doesn’t need a ground plane.

 

Ha, right! edit to fix; 1/2 wave . See this is why I leave the definitions to the pros while I'm only an amateur.

 

It's an end-fed center loaded 1/2 wave antenna. It's not a dipole.

 

Is this the Victory 4x4 mount? You may have said and maybe I missed it