SteveC7010

Correct. The SWR has to be checked with antenna and coax in their installed configuration. Otherwise you may get an inaccurate measurement.

No, but you will find some GMRS capable gear at a hamfest. If there is one near by, it’s a great source of parts, coax, connectors, towers, and much more, let alone radios. And it’s a good place to do some networking.

No, the CDM family is not type-accepted for GMRS use. It is Part 90, however. The low power (30 watt) versions of the CDMs can be knocked down to 5 watts channel by channel. They won't do the 0.5 watts required on channels 8 through 14. This means that you could set up a CDM for 5 watts on channels 1 to 7 and 30 watts for 15 through 22. Remember that the difference between 30 watts out and 50 watts out doesn't really give you 40% more range in most real situations. There's virtually no regular GMRS traffic in the area where I live except for a very few small businesses using bubble pack radios for in-store operations. If I chose to do so, I could easily setup a CDM for amateur and some GMRS channels and not interfere with anyone. They are rock solid radios with a very useful wide frequency spread. Regardless of what band you decide to use your CDM in, I heartily recommend the addition of a Motorola external speaker. It vastly improves the audio quality of the radio, and for high-noise environments, give extra volume. The right plug for the accessory connector can be ordered from ebay seller mre1032. If you do that, get the one that has the ignition sense line as well as the speaker lines.

I’d also point out the CB SWR meters are built for a single, very narrow frequency range and 5 watts of rf power. SWR Meters that work on GMRS usually cover a much wider band. My Diamond SX400 covers 140 to 525 MHz and up to 200 watts. There’s more sophisticated components necessary to do that.

CPS = Customer Programming Software

I’ve had very reliable results with a Diamond SX400 on both VHF and UHF installs.

The OP provided no information that would even remotely hint at a cause for the problem. Suggesting that it simply needs alignment is disingenuous at best. The radio needs to be evaluated by a competent tech. Once the problem is determined, the appropriate repair can be applied. Let’s give people good advice.

It’s just not possible to troubleshoot that problem via long distance and in a forum devoted to a specific radio service that is not normally used by EMS. There are too many reasons that can cause the radio to not receive and most of them are not easily identified without physically examining the unit It would best for a qualified radio tech to examine the radio and its installation in your ambulance. Given the critical nature of your mission, you should have a properly trained tech fixing your radio.

Good catch and a great fix! I suggest a light coating of dielectric silicone grease as well. The O-ring will slip into place easier and it’ll prevent corrosion. I put on the threads and center contact, too.

Your PM400s can be setup with front panel selectable TPL or DPL (but not both) which will depend on what’s commonly in use in your area. I run a PM400 in my truck for GMRS and am totally happy with it. With any of these radios, adding an external loudspeaker greatly improves the receive audio to your ear. I keep several on hand, all Motorola, of course.

Depending in your local codes, 35’ may be close to the max allowed. My village is 40’. Before spending any money on a taller tower, I’d use the 35’ one first and study the results. Get decent coax and connectors, too.

Foil HVAC tape available at any hardware or home improvement store. Sticks like crazy, handles weather just fine, and electrically conductive. Like JohnE says, great for ground plane on fiberglass or other non-conductive surfaces. I used to patch a slightly over-size antenna mount hole on an aluminum roofed utility trailer. Still going strong many years later.

And the batboard has plenty of info on a wide variety of Motorola gear.

Use a VOM multimeter.

Jim, Even with a decent quality connector, the mini-UHFs can be ornery. If it doesn’t want to stay snug, do this: Hand tighten the knob, being sure the little tabs are properly seated in their detents. You may have to hold it in place. Then GENTLY snug the knob with gas pliers just a bit, maybe a sixteenth to an eighth of a turn, no more.

Sent you a private msg.

Chassis! Modern vehicles have sensors linked to the PCM or BCM on the battery ground side. Use a factory grounding point on the body/chassis. There should be one or more near the battery. They’re easy to spot.

And, the ground side of the antenna’s coax is grounded to the radio itself.

Ground plane needs to be 1/4 wave length in all directions. For GMRS, that is a 6” radius around the base of the antenna. You can have just east/west and north/south radials like a base antenna but for a vehicle it’s more practical to use a disc of metal. I won’t get into the resale argument over the drilling the hole since your mind is clearly made up. But I do wonder where you’re going to find double-sided tape that is both weatherproof and 70+ mph rated.

Nope. Does not exist. Vanity calls are unique to amateur radio.

How are you planning on fastening a mag mount to a fiberglass roof? Typically, for fiberglass roofs like RVs and some commercial vehicles and ambulances, etc. we use a thick surface NMO drilled through the roof with an appropriate ground plane mounted on the underside. I like the 3/8” NMOs for this. For UHF, a minimum of 12” diameter is good. You can use most any conductive material such as sheet aluminum, metal window screen material, and more. The ground plane needs a good electrical connection to the ground side of the antenna mount to be of any use.

Grand Cherokees WJ ‘99-‘04 WK ‘05-‘10 WK2 ‘11-‘21 WL ‘22 and up We had a ZJ, a WJ and now we’re on our 2nd WK2, both with V8s and air suspension. The air let’s us jack the clearance up by 8” or so.

Go to ebay and search on “magnetic mic” without the quotes. I just got 1,000 hits, not all them what you want, but lots of them are.

Inside is fine. You could use metal window screen material, an asterisk of aluminum HVAC tape, chicken wire fencing, or any other electrically conductive material. Just make sure the ground side of the antenna mount makes good contact with the ground plane material. Probably have to use a “thick mount” NMO for a fiberglass roof. We do this all the time for ambulances, RVs, etc.

https://forums.mygmrs.com/topic/2440-raptor-liner-roof-ground-plane/?fromsearch=1