For GMRS you're fine. At UHF a quarter-wave is only about six inches, so a mag mount on a car roof or even a decent metal panel is already more ground plane than the antenna needs. The wall next to it will skew the pattern a little toward the open side, but it shouldn't stop it from working.
The bigger real-world hit in that setup is usually the coax, not the ground plane. 13 feet of the thin cable that comes with a UT-72 loses a noticeable chunk at 462 MHz, so if range feels soft that's the first place I'd look. Keep the mag mount on bare metal (or a steel plate), not on a painted plastic sill, and you'll be in good shape.
Dont park the antenna right against the brick if you can slide it a foot or two out. Small change, cleaner pattern.
Here is a detail from the photo. It shows a piece of flashing at the top of the roof (painted brown on top and bare metal on the side facing the camrea). It's quite narrow but it's probably 8' long. Would putting it on that work?
Probably, but check two things first. A mag mount needs steel to grab and alot of roof flashing is aluminum, so see if a magnet actually sticks before trusting it in the wind.
The ground plane also wants roughly six inches of metal out from the base in every direction, so a narrow strip mostly helps along its length. It'll still beat nothing, but a cheap 12 inch steel plate under the mount is the surer bet.
Standing wave ratio. It's how much power is actually being pushed out of the antenna and how much of it is coming back into your radio. You want it as close to 1.0 as you can, but anything under 3 is technically safe.
You can buy an SWR meter, if you do buy one, make sure it covers the frequency you're using. It's probably fine for you not to if you don't have it, if you're contacting the repeater, I'm sure it'll be fine. But when I first got my same style antenna, I accidentally broke the inside copper line somehow and my SWR was 18 which means 80% of the power was being reflected back into my radio and I was wondering why I wasn't contacting anybody. Just be careful to not pinch the coax in a car door or a window and you should be fine.
SWR, or specifically VSWR, is an indication of how much of the energy is propagated (forward energy) compared to reflected back into your rig (reflected energy). At 3 watts through a budget antenna is probably not going to hurt your rig. Also, your outside antenna setup, from the looks of it, should serve you well!
Oh boy, you’re either about to dive head first into RF engineering or you’re gonna get scared away.
SWR is stand wave ratio. It’s a measure of the antennas length ratio to the wavelength of radio band you are work with.
Basically an antenna works better if its size is matched to the frequency band you are working with.
I high swr can cause energy to be reflected back into the radio, at worst possibly damaging the radio, at least not allowing you to successfully transmit.
It would work OK--I have heard of people using cookie sheets for a ground plane.
There a guy who owns one of the local repeaters near me who makes and sells J Poles tuned to GMRS. Those don't need any radials or ground plane. There are others as well. Ed Fong is a notable antenna maker who makes the DBJ-UHF that he can ship tuned to GMRS. (The antenna is listed at the bottom of the linked page.) All you need to do is supply a specific spec pvc pipe for the antenna (he gives stock numbers and this is cheaper than what the shipping would be if he included the pipe.) The endcaps are supplied. These are just a couple of options if you are looking for something not needing a radial or ground plane.
You can also get a N9TAX Labs antenna tuned for GMRS that requires no ground plane. I have one hanging in a really BIG second story window in my house and it works really well.
Yep, I've heard good things about those. The only reason I don't have that for my ham HT is that Prof. Fong;s DBJ-2 is a better dual-band antenna for 70cm and 2m. But N9TAX's antenna would be just fine for single-band use. For GMRS, the DBJ-2 will work OK though it's not specifically tuned for GMRS. I would not be against getting a GMRS-specific antenna later for road/base camp use.
The Fara-J antenna, while pricey, is another I have heard good things about and I'd consider that as possible antenna to take on the road with me--especially since you can roll it up pretty tight. I have an arborist's line as well as a tripod and collapsible mast that I attach it to for when I'm out and about.
I was thinking about doing the same but Google searching led me to different little copper spikes instead of one solid piece of metal... I think mostly for wind not launching the setup into New Jersey
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u/Extension-Mall-7292 2d ago
I thought that was a tortilla shell for a min...it's been too long since I had tacos