The radios don't come with a programming cable, but it's pretty easy to make one. The cable is based on an article by Miklor. I used a CP2102 breakout board that I got on Amazon and some really slick metal stereo phone plugs fom Adafruit. You'll need a 3.5 mm and a 2.5 mm plug.
The thing I like about the markings on this breakout board is that they leave no ambiguity:
RXI (Receive In) is a "gozinta"
TXO (Transmit Out) is a "gozouta"
It turns out that the phone plugs don't clear the radio's body so even though they look like they're fully seated, in fact they are not. I had to unscrew the backshells a few turns to get them to make contact. I found another disadvantage of metal backshells: if you touch the springy strain reliefs together, the radio goes into transmit mode! Next time I'll use plastic backshells.
Connect the plugs to the CP2101 like this:
Now you can start editing your CHIRP spreadsheet. Use "Input from data source" to populate the spreadsheet with repeaters. You can also enter stations like your local NOAA weather channels. Here's another thing you can't do from the front panel. Change the station's entry in the "duplex" column from "(None)" to "Off". This disables the transmit function on that channel, so you don't accidentally key up on it. You may also want to set the value in the "Skip" column to "S", so scanning never stops on the weather channel.
When you program the radio, it's best to turn the volume up to get maximum signal into the PL2101 breakout. Also, when you are downloading from or uploading to the radio, although there's a warning about this, and the status LED flickers, but it doesn't really appear to go into transmit mode. All the same, it may be a good idea to go to an unused channel, and set the power to low, or to use a dummy load.
When CHIRP asks you for a port, you will see something like "/dev/ttyS1" at the top of the drop-down list. Scroll down to the very bottom to find your USB port, which is going to look something like "/dev/ttyUSB1".
When you're using CHIRP, you can expect to see the radio's status LED do the following:
Read: Flickering Green/Amber
Write: Flickering Green
Now there's one more thing to be done: change the display to show the repeater call signs you entered in CHIRP. Go into the radio's menu from the front panel and set MDF-A to "name". I've left the B channel on "freq" so I still have the option of selecting channels by frequency.
As a bonus, here's one more cheap radio programming trick. The QYT KT-8900R has a library file that may not yet be included in the version of CHIRP that you installed. You can get it here: https://chirp.danplanet.com/issues/6265, but there's a typo in the code, so you will have to search for the string "radio.id2" and change it to "radio._id2".
