dosw

There's a good observation here: "ham vs GMRS" doesn't help. People wanting to establish a good GMRS repeater would get a lot more traction on such projects by working *with* a ham club. In my area there are a lot of really good 2m and 70cm repeaters. And the groups operating those repeaters have solved a lot of the hard problems. If you can build a good relationship with them, you might get help navigating the waters of setting up a GMRS repeater.

It would be very hard to find a mass produced antenna with so much gain that it would cast its signal too high or too low for another antenna at a 140 foot offset 20 miles away. That's 0.00135%, or 0.076 degrees. That level of focus of signal is in the realm of laser beams, or antennas for communicating with equipment on the moon. Another way of looking at it is that a boat's radar, which is designed to have good resolution characteristics, could merge two objects into one if they're less than 300 feet apart at 20 miles.

RF line of sight could be a problem, depending on how high you can realistically mount your antennas. An antenna mast with mounting hardware could easily set you back a couple hundred, to get your masts up 30 feet. On the other hand, mounting each antenna fifteen feet up on the roof, with one property 140 feet above the other property, could get you right around 20 miles. This is good news because it also means RF line of sight roof-top to roof-top is something you can verify with a couple of inexpensive handheld radios. So before buying nice radios, and before buying masts and antennas, buy a couple cheap GMRS handhelds for $30 each. Each of you stand on your roof. And try to talk to each other. If you get nothing, no static, no roger beeps, nothing, you're just out of luck. Those wooded areas between you are attenuating too much of your signal. On the other hand, if you're able to break squelch and hear each other a little, you can proceed. Now assume that you were able to break squelch for each other. What next? Each of you get a 25w to 50w radio, however many feet of LMR400 cable you each need, lightning arrestors, some fittings, and appropriate mounting hardware for the roof. Get a couple of antenna such as the Comet GP6NC GMRS antenna. Oh, and get 13.8v power supplies. Adding it all up you'll be spending around $525 to $725 each. As for repeaters; a repeater is useful if it can be higher than the other radios, and/or positioned somewhere between the other radios. It's useless to put a repeater on your roof, if the goal is just to extend range from your roof to the other person's roof. A repeater won't be giving you more range. What a repeater does is it allows one radio talking to the repeater to hear another radio talking to the repeater. If A and B cannot hear each other, but A can hear C, and B can hear C, then putting a repeater at position C will allow A and B to hear each other by talking through C. Another thing to do is to investigate what ham repeaters are in your area. If there are no GMRS repeaters, you may discover there *are* ham repeaters. Then you get licensed for whatever type of repeater exists in your area. If you find GMRS repeaters, great, get your GMRS license. If you find ham repeaters, you and the other party need to study for a couple weeks and get your ham licenses. If you are fortunate enough that there are good repeaters in your area (ham or gmrs), then you don't need to spend 500-700 each. You can each get a $30 radio that is made for the service type you're getting licensed in, and talk through the repeater. In my area there are about seven or eight pretty good GMRS repeaters. But there are also at least 25 very good 2m or 70cm amateur/ham repeaters. If that ratio holds true elsewhere, even if you don't have a GMRS repeater in your area, you may find there are one or more decent ham repeaters.

Set his radio to channel 8-14.

This is true. Out my window I have an MXTA26 antenna on a Midland magnetic mount, on a sheet of steel sitting on top of a window air conditioner. Fortunately it's not in a place where anyone would see it, because it does look janky. But it works fairly well, and the whole thing is antenna (70), mag mount (40), adapter (10), sheet of metal (had in the garage): $120. I really doubt you could do a base-station antenna installation with LMR400 for less. And with this, I have no problem hitting a repeater 64 miles away with a handheld hooked up to the antenna.

Does LMR400 plus a $70 antenna and a resonable mount break the budget? I guess staying below 100 is a pretty tight constraint. Be aware that you will probably want an antenna designed for "base station" use. A mobile antenna likes a vehicle body beneath it, whereas base station antennas usually have radials included with them. Anyway, here's the very useful cable loss calculator: https://kv5r.com/ham-radio/coax-loss-calculator/ With this calculator you can experiment with different antenna gains and cable types to see what meets your needs. At 50 feet, you're going to want decent cable.

A true GMRS radio is not that complicated; you switch to a channel (1-22), make sure that neither radio has tones enabled, and then just start talking. If you add a tone (CTCSS / PL, or DCS), you will need both radios to use the same tone. Midland gives its tones different numbers than other manufacturers, so you might have to look up in a crossreference table in the manual if you have a Midland. That's it for radio-to-radio communications. All GMRS radios should be compatible with all others at this level. Then getting into repeaters, you'll need to select the correct repeater channel (sometimes named 15R, through 22R, sometimes R1-R8, sometimes R23-R30), and the correct tones for that repeater. But any repeater-capable GMRS radio will work about the same way, and all should be compatible so long as they support repeaters in general.

Absolutely correct. FCC rules for GMRS Channels 8-14 have the following restrictions: Only handheld portable units The effective radiated power (ERP) of hand-held portable units transmitting on the 467 MHz interstitial channels must not exceed 0.5 Watt. Each GMRS transmitter type capable of transmitting on these channels must be designed such that the ERP does not exceed 0.5 Watt. Bandwidth: narrowband; 12.5 kHz for GMRS transmitters operating on any of the 467 MHz interstitial channels Deviation: on the 467 MHz interstitial channels must not exceed ± 2.5 kHz, and the highest audio frequency contributing substantially to modulation must not exceed 3.125 kHz. Accuracy within 2.5ppm of channel center Also, you cannot design a radio to have a maximum effective radiated power of 0.5w if you don't control what antenna is used, since antenna gain is a factor in ERP. So it might be an oversight but I don't see in the regulations where it says that on 8-14 the antenna must be a fixed antenna. I just noticed today that even channels 1-7 are supposed to have their power calculated by ERP. The "mains" don't have that limitation; 50w is the maximum permissible on repeater inputs and primary 462 channels, measured at the feed line, not in ERP (and nobody cares, nor should they). Anyway, no type approved GMRS mobile radio would be approved if it could transmit on 8-14.

I don't know why someone would specifically want a mobile radio that transmits at 2w. Nothing wrong with 2w if that's all you need, but it's a weird requirement. But the MXT-105 is 5w max, and has a low setting that is probably very close to two watts. I haven't measured, but guestimated using paper napkin math and hunches, based on its advertised power input requirements at low and high. If someone has this whimpy radio and a power meter, they could confirm. But they'll likely find low is about 2 watts.

I do the same. I was just curious what bandwidth problem he thought we would be out of compliance on

Which bandwidth requirement are you looking at? GMRS allows 5kHz deviation in channels 1-7 and 15-22, along with repeater inputs. It's not out of line with what 70cm ham radios will emit. Usually where ham radios are problematic is that they often won't transmit as low as 0.5w ERP unless you're transmitting them into a dummy load. So channels 8-14 are often impossible to be in technical compliance on, when using a ham radio.

Thank you, I'll check them out. I've looked into the SBB-5 but couldn't tell if it's NGP or not. Its product sheet says something like non-radial, but the CA2X4SR says the same on its product sheet, and definitely needs a ground plane.

Open to suggestions. The criteria: 2m, 70cm, GMRS. Acceptable SWR with a lip-mount with its inadequate ground plane (pictured in my original post). Mobile NMO mount I have the following, already: Laird/TE B4505CN - GMRS only, no ground plane required. Works great in that application. 5dBi gain. MXTA26 - GMRS only, prefers a decent ground plane to achieve reasonable SWR. 6dBi gain. MXTA25 (ghost) - GMRS only, ground plane preferred to achieve <2.4SWR. 3dBi gain. HYS-1T - GMRS only, 3dBi gain, ground plane required for reasonable SWR. Comet CA2X4SR-NMO - 2m, 70cm, GMRS. Fantastic with a good ground plane. Poor SWR with an inferior ground plane. I don't mind buying the right thing for my application. The Larson NMO2/70B seems to check the boxes, but if there's something better I'm overlooking please let me know.

Thanks so much!

I'm wondering if anyone has used the Larson NMO2/70B, and if they have an antenna scan from it mounted in a hood-edge location. It's supposed to be 1/2 wave at 2m, colinear in 70cm. I'm looking to see SWR curves that cover amateur 2m, 70cm, and GMRS. My Comet CA2X4SR isn't going to do it because of my mount location. Its SWR gets out of hand in weird ways. ...and the antenna in the picture is a Laird/TE B4505CN, which is a great match in GMRS, and even extends into upper 70cm alright, but has an unusable SWR in 2m. If there are other options to consider I'm curious to hear.