What is the Difference Between Simplex and Repeater Channels?

From the beginning when I learn the ham radio knowledge, There are two basic ways to using your radio. One is simplex, the other more popular way is using a repeater. I often get confused how to operate a radio connect to a repeater, the shift frequency downlink and uplink.Today, let us learn the difference between simplex and repeater.  

Simplex, it is very easy to understand, for the radio, Use the same frequency, transmit from radio A to radio B. All the configurations are the same. Two radios can communicate with each other.

But for repeater, you should to know what is a repeater, the repeater frequency, shift offset?

The repeater is a device consisting of a transmitter and a receiver. It picks up your transmission and simultaneously re-transmits it. Usually the repeater will have much greater range than you will if transmitting from a handheld or mobile radio. 

Downlink frequency: this is the repeater transmit frequency which you need to set as a receive frequency on your radio.

Uplink frequency: this is the repeater receive frequency which you need to set as a transmit frequency on your radio.

From this we can know that the repeater use two different frequencies, they have a shift offset. For 2M it is .600Mhz (or 6Khz) and for 70cm(440) it is 5Mhz. You also need to know shift direction +up or –down.

Another important thing need to know: for an analog repeater, you need to know the access tone, also can say CTCSS/DCS. The tone is not always used, but if the repeater is programmed for a tone then it will not repeat any signals it receives that do not have a tone on it. But on a digital repeater, you need to know color code set on the repeater.  

You can find many repeater information on repeaterbook website like below picture show.