Two points based on the above replies.
1) LMR-400 (or most any of the foil over braid types of coax) should not be used in a duplex environment such as a repeater using a duplexer. The two metals used for the foil and braid will cause issues with PIM (Passive Intermod -
Passive Intermodulation (PIM): What You Need To Know | Wireless content from Electronic Design). There is a difficult to find and more expensive version of LMR-400 that has low PIM, but if you're paying for that, you might as well use the real stuff, like LDF4-50A that will give you lower loss and no PIM. Some folks claim to have success using LMR-400 on their repeater, but often their operation is not duplex (separate TX and RX antennas for example), their installation is new enough so the issues have yet to happen, or they simply have yet to discover that their issues is due to the coax, that otherwise tests out to be just fine.
2) There are comments about a standard duplex repeater (the signal goes in and nearly immediately goes out with zero or at most minimal delay) and a simplex repeater (the transmission goes in and is recorded, once it stops, the simplex controller turns on the transmitter and replays the recording so there is a significant delay in the conversation.
The duplex repeater is what most of the repeaters you hear are. They take two frequencies, and input frequency that the users transmit on and the repeater listens on, and an output frequency, that the repeater transmits on and the users listen to. The duplex repeater is more expensive since it requires more expensive and robust hardware. A typical user radio (like those boefangs mentioned) can be made to work, but will often burn out due to overheating since they were not made for the long transmit cycles a typical repeater has.
The simplex repeater uses a single frequency (although separate input and output frequencies can be used if available) and just a typical user radio can generally be used. Overheating can still be an issue, but generally the transmit cycle is similar to how a user uses their radio so no specialized radios should be necessary. The controller is the difference between a user radio and a simplex repeater. It monitors the assigned frequency and records a transmission. Once that transmission is done, the controller turns on the transmitter and repeats the transmission for its duration and returns to receive, waiting for the next transmission. If you're able to hear both the original signal and the repeater signal, it'll sound something like this...
(Joe's transmission) "Hello Bob, I'm sitting on my favorite chair using my handheld, trying out your new simplex repeater."
(Repeater's retransmission) "Hello Bob, I'm sitting on my favorite chair using my handheld, trying out your new simplex repeater."
(Bob's reply) "Thanks Joe, hope it's working as well for you as I intended."
(Repeater's retransmission of the reply) "Thanks Joe, hope it's working as well for you as I intended."
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