I recently needed to re-program my FT-857D with some new memories but didn’t have a spare USB CAT cable to hand. Then I remembered that all of the various radio programming cables use just 3 wires, I opted to make my own Heath Robinson version which took longer to assemble on the desk than the actual programming cycle itself!
I used an FT232RL FTDI USB-to-Serial converter which also make great Datamode Interfaces for older radios without a built-in USB/Sound interface. Typically, the PTT is wired to the RTS and CW keying comes from the DTR pin. For programming radios, the TXD+RXD pins are cross-wired to the radio along with the Ground.
Here’s how the thing goes together:
My wires were a couple of Dupont ribbon cables which were stripped and pushed into the connector on the radio. The jumper on the TXD+RXD pins was obviously removed. So, in summary, the TXD pin of the interface goes to the RX D pin of the radio, and the RXD of the interface takes data from the TX D pin of the radio (eg: null modem cable)
…and that’s all there is to it – I used G4HFQ’s FTBasicMMO to update my radio but CHIRP would also do the job.