a simple remote gmrs repeater installation

Well it’s been a minute since I’ve posted anything, which is a post all on its own, but let’s get right into it. I’m a general license holder, and a few years ago commented that maybe you should be a ham radio nerd too. But much less nerdy and much easier for the average citizen is a GMRS radio. For $30 and no test, you can get a 10 year license for yourself that covers your family too. GMRS, like 2m VHF, is line of sight: if one radio can see the other one, you’re golden. Throw some trees in the way, and definitely a hill, and you’ve got nothing.

The way of solving this is a repeater, shown below.

Basically the repeater is a radio all on its own. It receives on one frequency and simultaneously broadcasts on a second frequency. The handheld radios have a special entry that basically says “listen on this frequency and when the talk button gets pushed, transmit on this other one.” If there was a repeater and someone handed you a radio that was configured to use it, you wouldn’t know the difference.

I’ve obfuscated and hidden a lot of the data about this repeater because while it’s legal to be where it is, it’s a few hundred dollars of equipment just sitting out there hanging out. In short, it’s very high up on peak which is where you’d want yours to be as well. I can’t overstate enough: repeaters are all about line of sight. If the antenna has a clear view of another antenna the signal will get there. It is almost always the case that higher is better. One thing I’d recommend is a free tool called Radio Mobile Online. With it, you’ll be able to drop pins and model coverage to help you sort out what works best. Here’s an example of a hypothetical 2m repeater pushing 75 watts up on Montgomery Peak.

My goals for my repeater were to be able to cover a given area, with certain places in particular. I wanted something portable enough that I could backpack / lug the whole thing up a gnarly class 4 and scree field. I wanted it to survive the winters and not get sun damaged through the summers. Checking in on it every year is fine for me.

So like every recipe on the internet now that I’ve bombarded you with a bunch of garbage you don’t need to know, here’s the guts of the GMRS repeater I have online now.

• Antenna. I opted for a Harvest BC200 antenna which is designed for GMRS, seems quite durable, and stands about 6 feet tall. I secured all the fasteners with blue loctite, and gave it a quick coat of light blue spray paint. The goal of the paint was to blend in better with the sky and to be one more layer standing between the sun and the fiberglass.
• Base. I welded my own out of 1/8″ thick 2″ angle steel. It has one vertical element that the Harvest antenna fits well onto, and three feet which I stacked heavy rocks on. I used a bubble level to make sure the base was flat as I got it situated. Conveniently the antenna grounding lug is connected to the metal base, and the metal base has broad contact with the ground.
• Repeater. The guts of this setup is the repeater itself, in my case the Retevis RT97. It’s low power, but that’s actually pretty cool because that also means it uses less power, needs a smaller battery, and a smaller charger. With a clear line of sight I’m getting 39 miles. I programmed it with squelch tones which a smart person could figure out (if you also knew where the repeater was) but it will keep the general public off of it unless they have those tones.
• Solar charge controller. I went with a cheapo Binen model, it charges the battery and it supplies ~13v to the repeater. Part of why I configured it this way is that if the battery dies the controller will still supply power to the load (while solar is being generated).
• Battery. I’ve used one of these before for another project, so I went for a UPLUS AGM 20AH battery. I’m a sunny (but snowy) area, and those 20 amp hours really means I can use 10 amp hours before hurting the battery. The RT97 pulls about 5 amps while transmitting, so that gives us about 2 hours of talk time only running on the battery. It could get up to 4 hours in an emergency but the battery would take a hit (long term). For us, since this is not an open/public repeater with lots of people chit chatting (rag chewing) through the night, this is more than appropriate. Most of our usage is during the daytime where there is ample solar power so talk time is unlimited during the day.
• Enclosure. I went with an MTM ammo case, it’s not bullet proof but I really just wanted water resistance.
• Cable. I opted for RG213. While not as good as LMR400, I have a lot of experience with RG213 and since I managed to keep the wire run short (20 feet) the loss difference between RG213 and LMR400 is negligible at that distance.

Edit: Feb 2024: I haven’t put the the repeater on a power monitor but it looks like the actual power draw when transmitting is about 2 amps @ 12 volts, so 24 watts. Rounding up to be conservative you could say 25 or 30. Either way, that’s half of the power consumption from my initial calculations so my 20AH battery can transmit for 4 hours without issue, or 8 hours in an emergency.

So now some pictures, and some notes.

The guts above. Battery on the right, repeater on the left, charge controller on the bottom left. It’s hard to see, but I used galvanized metal pipe fittings to penetrate the box, flanges, with 45 degree down angles. You can also see a flange bolt in the top left where the RF cable exits. The thin power lines are for the power supply of the repeater, the larger (and barely fitting) power lines are coming from the solar panel. Yes, the wiring could be improved, but it works. The plastic box got a can of spray paint to give it a little more UV shielding.

The ammo can with the guts is closed up and has cardboard over it, again to shield it from the mountain sun. Being up so high we have extreme UV radiation. It’s hard to see, but top left you’ll see the angle steel mast sticking up with some bailing wire wrapped around it, the RG213 cable is in the groove, with the steel point aimed south so the cable is in the shade as much as possible. The solar panel is there on the right, with large diameter wire wrapped around stout rocks. The angle is extreme for the winter sun and to shed snow.

The antenna, prior to its sky blue paint job, sitting on the angle steel mast. The height of the antenna last is really not that critical if the overall placement is high. As in, I’m at least 1000′ above anything that can see this antenna so the mast is only ~3 feet tall. The antenna is another 6′.

In summary, my repeater works for my purposes. There absolutely are better ways of doing this. The wiring could be better, the antenna could be professional grade, the battery could be larger, the whole thing could be higher. Do your thing, and maybe this will help give you some ideas.