I dug out an old radio interface that I built some years ago, the design was actually part of an article on eHam.net:
Anyhow I've had this bit of kit to pieces today and will be doing more fiddling with it tomorrow.
I have always had difficulty getting the TX and RX LEDs to function correctly so I've added some separate circuitry to do that today. Somehow I misread a relay and I've managed to regulate down the +13.8V supply going into the box to +5v - this is driving a 24V relay! Muppetry!
So tomorrow I'll play some more and swap out the relay for a 5V unit I have here.