I was planning to do a look at the official firmware for this radio, then I realized that a lot of people have already done that, so I went straight to looking at OpenGD77 on it. This is my first impression. Also, Retevis officially supports the loading of OpenGD77 on the radio.
This radio was provided to me by Retevis free of charge in exchange for some videos about the RT3S and OpenGD77. I did not pay for this radio except for import fees and sales tax, but I was not paid to make this content either. All opinions are my own.
You can get the radio here:
http://bit.ly/3TPIIGy (Sponsored link)
If you would like more information on OpenGD77 you can check out these to links:
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Note: The antenna design is now open source and can be found on Thingiverse.