Jones

Heat has not been an issue with my Kenwoods. They will not get hot enough to set anything on fire, or melt plastic. They will need a bit of airflow around the heatsink however, so don't bury them under anything, or mount them in an enclosed area without ventilation.

NOTE: RG-400u is NOT the same type of cable as LMR-400 or DX-400.  RG-400u is a smaller diameter, double-shielded cable, the size of RG-58u, for use as jumpers in a repeater system, or internal radio connections where signal leakage would be a problem.
 
LMR400 from TImes Microwave and its clone, the DX400 cable from DX Engineering is a larger cable, the size of RG-8u, that is supposedly rated for use up into the 400 MHz range with low-loss. It has its uses, and can be great for a GMRS base station, but not a repeater where it has to transmit and receive at the same time - that is where the trouble starts.
 
RG-400u, and its larger cousin RG-214u are Mil-Spec double-shielded, silver plated cables, specifically designed so that the signals between two closely-ran cables will not cross-talk into one another.  That's what you need is a repeater system.

One thing to keep in mind is what kind of range you will actually need.  For example, if you live in the center of a valley surrounded by tall mountains 5 miles away in every direction, there is no point in spending a lot of money for extra power or to reduce cable loss.  For example 20 watts into a 6db loss feed line might still cover the entire area quite well.
 
Also consider the criticality of the system. Is this just for fun and maybe a backup for a cell phone. Or, is this your sole means of communications. Once you answer that question, budget accordingly.
 
And, also step back a bit and look to see if there is another way to organize your installation. For example, instead of locating the radio 50 feet from the tower, can you create a small enclosure and house the radio at the base of the tower.  A good quality weatherproof garden shed, or even a large tool-box, might cost a lot less that 100 feet of high-end feedline.

Half the time I see people blaming a "bad duplexer" - it turns out to be the junk cables connecting the repeater to the duplexer. You should be using a good quality double shielded cable like RG400 with the correct ends (no adapters!).  Type N is the preferred connector, but if your repeater or duplexer has different connectors, you need to work with those.
 
Try someone like these guys  - avoid the cheap "tin" or nickel plated connectors - there's a few USA based sellers with similar products: https://www.ebay.com/itm/6-10-RG400-M17-N-Male-Clamp-Jumper-Silver-coated-RF-cable-USA/131269263466

I still think you are describing de-sense.  The one weak link you have in my opinion is that knock-off LMR-400 coax cable.  I also still wonder what you are using for jumpers between the radios and the duplexer.  Cheap CB coax jumpers will NOT work for that purpose.

If you want something lightweight that folds down for "just grab-and-go" temporary use, I have had good luck with PA system speaker stands such as:
 
https://www.parts-express.com/peavey-tripod-speaker-stand-ii-56-102-black-100-lb-capacity--248-8586
 
Add a 5-foot mast pipe to the top of this, and your antenna is instantly 12-15 feet in the air.  Add some rope and tent stakes for temporary guy wires if it's windy.

If you want something lightweight that folds down for "just grab-and-go" temporary use, I have had good luck with PA system speaker stands such as:
 
https://www.parts-express.com/peavey-tripod-speaker-stand-ii-56-102-black-100-lb-capacity--248-8586
 
Add a 5-foot mast pipe to the top of this, and your antenna is instantly 12-15 feet in the air.  Add some rope and tent stakes for temporary guy wires if it's windy.

Separate conductors also are much better at heat dissipation. Important in the event of a long-term overload that does not trip the breaker.  

As a contract radio broadcast engineer, I am on the road a LOT in Nebraska and Kansas.  I very rarely hear anything on GMRS other than my own family, but I did just a few weeks ago hear a couple of truckers on 462.675 (Channel 20) on hwy 81 north of Salina.
 
I usually monitor either 462.675 (20) when I'm on the road, or 462.625 (18) when I'm around my hometown, since my family uses 625.
 
Channel 20, with a CTCSS tone of 141.3 (Midland "privacy code" #22) is sort of the "official/not quite official/depends who you ask" traveler's channel for FRS/GMRS, so that is where like-minded people should hang out if they want to have a chance at talking to someone else on a road trip.
 
So, one-way to Kansas?? Where in Kansas, and why?

Calm down, have a beer.  .....Yes, I'm OK now.

As a contract radio broadcast engineer, I am on the road a LOT in Nebraska and Kansas.  I very rarely hear anything on GMRS other than my own family, but I did just a few weeks ago hear a couple of truckers on 462.675 (Channel 20) on hwy 81 north of Salina.
 
I usually monitor either 462.675 (20) when I'm on the road, or 462.625 (18) when I'm around my hometown, since my family uses 625.
 
Channel 20, with a CTCSS tone of 141.3 (Midland "privacy code" #22) is sort of the "official/not quite official/depends who you ask" traveler's channel for FRS/GMRS, so that is where like-minded people should hang out if they want to have a chance at talking to someone else on a road trip.
 
So, one-way to Kansas?? Where in Kansas, and why?

At its heyday, CB was a social event, the Internet of its time. People bought CB radios because they didn't want to miss out on what was happening. CB was the end, not the means to an end.  I would guess that a huge percentage of CB radios were trashed within a month of purchase.  As you summarized from the responses to your original post in this thread, people get into GMRS to support some end that exists outside of "radio."   So, the picture to me is any group of people engaging in some activity, which could just be their daily lives, who have a need for simple, reliable communications to support that activity.

Thank You Jones that does make it pretty simple. Ive always loved radio communications of all types and how they work.

To make it real simple, and Midland friendly, Yes.  You may talk between your FRS radios and your Micromobiles on channels 1-7, and 15-22. 
 
(NOTE: To make this even simpler, channels 8-14 are not even included on the Micromobiles - it skips over them.)

Wow, pleasant, accurate and polite exchange of information? Am I still on the Internet? I would have asked the same question in a few days Scarleton. I'm new at this and would love to see a follow-up here on how your radio works with the repeater. 
 
And Mr. Jones, thank you for the polite and information-packed response.
 
Happy Fourth of July everyone.

For a small part of the path to the repeater... that's it.  That's not real contact.
 
I had someone bragging to me about a 2m C4FM contact to an operator in Japan over a digital group and he logged it as a JP contact in his log.  I told him to give me a break.  If using my radio to go 2.5 miles to an internet-linked repeater and digital chatroom counts as a JP contact, I may as well just call a random person in Japan on the phone and count that as a JP contact, too.

I'm not an old Ham... but if you're talking to someone over the internet, that isn't radio, in my opinion.  The whole point is to use airways to talk.  If you are using the internet, you may as well be on a computer or smartphone.  I especially feel this way about people using their smart phone to get into a group and they aren't even on a radio. 
 
If 2 people are using their smartphone to talk to each other though a Fusion or WiresX web app, how the heck is that Ham radio?  If that counts, anyone who talks on a cell phone may as well consider themselves a Ham.  LOL

I hear DTMF tones all over Nebraska on MURS.  I looked into it a year ago, and found out that several farms in the area use MURS for a remote monitoring and telemetry system for their crop irrigation systems and water wells.  There is also at least one company making MURS remote alarm systems for farm buildings and gates.
 
MURS is legal for all of those kinds of things, so that's likely what you're hearing.
 
Most people using MURS for these types of operations do not even know what frequency or band they are using.  All they know is that they purchased this wireless thing that lets them know back home when someone opens the pasture gate, and they have another wireless thing that tells them how many gallons per minute the pump is flowing.

To summarize WPXM352’s excellent response to your question… One of your club members is an expert the other is not.

Yeah while field day is centered around amateur radio, I feel its a great opportunity to expose folks to the utility that GMRS offers. I've found a great community of like minded people around GMRS that may have never delved into amateur radio otherwise. I plan on activating 20 meters mainly and calling on the local GMRS repeaters for general conversation to learn what others are doing across the US. WQYM541 good luck on your trip! I hope to hear some of you on the air.

I'd be concerned with anyone who let a repeater go out the door & didn't check the duplexer the first time. If he didn't get it right then, what's the chances he's going to get it right this time? It sounds like you bought it from the seller as a working package.
 
Before you send it back - make sure you've got the cables hooked up correctly  - the High side should be to the Receiver, low side for the Transmit. I've seen too many jumpers crossed up not to ask.

If all the parts come in, I'll be traveling across northern Kansas this weekend trying to get a 30,000 Watt signal, and two 100,000 Watt signals back on the air in the 3-Meter band. (a.k.a. FM Stereo)
 
I might try some simplex on 146.520 in the 2 Meter band while I'm on the road, but unfortunately, I won't be able to play with amateur radio much during this year's field day, since I'll be busy with commercial radio.

Run 4 watts.

Midland GMRS radios are not programmable.  They are fixed with GMRS channels, and that's it.  Also, you can find MUCH better antennas than Midland's junk, and for a better price.
 
That link is for Midland Biztalk series business-band part 90 radios.

I don't think he is talking about the signal actually being repeated, I think he means the signal comes in on his radio on both channels - in which case his receiver is not alligned properly, or it is a CCR with a lot of unknown IF leakage.