"two radio" duplex repeater

Another question for you guys,

Lets say i have two motorola radios.radio #1 is recieving a message and this radio has a headset plugged into it. If i splice the headphone from radio #1 onto a mic on another headset (#2), would headset #2 be able to transmit simultaneously? Basically id like to build a duplex repeater this way. I believe they have some already for higher grade GMRS radios and are referred to as back to back repeaters or something?

In the most basic sense, yes, this is what happens.

But the devil is in the details.

You have to match the audio levels coming out of the receiving radio and going into the transmitting radio. You have to have a way for the receiving radio to ‘tell’ the transmitting radio that it really is time to transmit, and when it is not time to transmit.

You have to make sure that the comparatively large power of the transmitter doesn’t overwhelm the very sensitive receiver; and making sure that the frequency separation between the two is large enough will help this, tho there are practical limits. These and other considerations are the function of a device called a ‘duplexer’, which lets the transmitter & receiver share the same antenna.

Welcome to the world of engineering radio systems!

Unless you are a real hobbyist or engineer and enjoy jacking around with this (and you may or may not ever get it right) you can buy a repeater maker. Why try to reinvent the wheel? This unit costs around $300.00. I have used it in the past and it works great.