You can use one USB to serial converter cable and adapt it to multiple devices, but you need to match voltages. Devices can either be
- RS-232 (-12Vdc to +12Vdc, or more commonly -5Vdc to +5Vdc). This is the good old-fashioned serial that has all but disappeared from modern electronics.
- TTL (0 - 5Vdc)
- LVTTL (0 - 3.3Vdc)
The Chinese radio manufacturers (or maybe I should say accessory manufacturers have come up with an answer which could be a blessing or a curse. They are now selling 6-in-1 or 8-in-1 radio programming cable kits which include one USB serial adapter which brings out 3 wires (RX, TX, Gnd) in a 3.5mm TRS phone plug/jack set. There are a set of cables to adapt to a number of different radio styles.
The Good news -- These are available for around $10 and should be useful to peuple who own multiple radios or need to program other people's radios, like clubs and emcomm groups.
The Bad news:
- The converter is based on, you guessed it, the same crap counterfeit Prolific chips that fill every group I read with the same driver related questions over and over.
- Because it's plug and pray, it will be easy to experiment and possibly/probably damage some electronics.
- Adding TX/RX LEDs to assist with diagnosis
- Adding over-voltage protection
- Detecting and protecting against reversed connections
- Ability to get at RTS/CTS lines for other uses.