I have two existing rt-21 radios. I have purchased another two RT-21 radios. how can I make all four radios communicate with each other

Dear,RT21 is analog model radio,for analog radios communication, just set all communication channels with same frequency and CTCSS/DCS is ok. Please download USB universal driver and RT21 software from Retevis official website freely: https://www.retevis.com/resources-center For the same model of radios,related video for your reference: https://youtu.be/_sSkPdW1u7Y,please try it.
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