I have recently acquired an Allied Telesis gs950/24 switch. The only problem is that this is the older version (non-eco) and has a console port. The… More on reddit.com

This is the "famous" Keyspan: https://www.amazon.com/Tripp-Lite-Keyspan-High-Speed-USA-19HS/dp/B0000VYJRY/ It uses a Texas Instruments chipset and is very stable, and works like a champ. This is the less famous IOGear GUC232A: https://www.amazon.com/IOGEAR-Serial-RS-232-Adapter-GUC232A/dp/B000067VB7/ It uses a Prolific PL-2303HXC chipset, and is roughly half the cost of the Keyspan. The Prolific chipset devices tend to change COM ports when they feel like it and have a somewhat negative reputation largely caused by low-quality counterfit devices. I've been using one of these IOGear units for years. Someday when it dies, or if I need to move to USB-C, I'll probably upgrade to the Keyspan (which is available in a USB-C version). It doesn't really matter, so long as you buy an authentic product that is well manufactured. More on reddit.com

USB to RS232 Adapter with PL2303 Chipset, CableCreation 6.6ft USB 2.0 Male to RS232 Female DB9 Serial Converter Cable More on reddit.com

I think you can actually just use the Tx and Rx pins to use the arduino's uart converter directly without programming. Connect the arduino's ground to the radar's gnd. Plug in the arduino to usb, turn on Serial monitor , then Plug your radar's Tx into Rx. (If that doesn't work, try plugging it into Tx, I forget which sense it is) More on reddit.com