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1  I purchased 5 rt21 radio's and the disk to program them with the cable; but it does not work with windows 10. can you send me a link to the correct software?
Please download RT21 usb driver and RT21 software from Retevis official website: http://www.retevis.com/resources-center/ Attached a photo for you reference:
2  Hello Where can I download the programming software for the RT21 and RT81? Thanks and Greetings Stephan
A blog about how to program radios : http://blog.retevis.com/retevis-radio-frequency-programming/
3  After the download the software for RT21 shows error message and can not be used. With RT1 and H777 everything is OK. Need a solution otherwise i have to return the equipment to the seller. Greeting Ralf
Any pictures to show the error ? Or you could try to program by Chirp -- http://chirp.danplanet.com/projects/chirp/wiki/Home