Since getting headphones, the mains hum on my Kenwood TS-2000 needed to get sorted as it was really distracting.

To confirm the source I powered the rig on a battery and the hum was still their, unplugging the antennas made no difference until I unplugged the RS232 serial lead to the PC, at that point the hum stopped, I then powered the rig from the Power Supply Unit and the hum only reappears when the serial lead is plugged in.

The issue stems from the fact that the PC running Ham Radio Deluxe (HRD) radio program is fed from an Uninterruptable Supply and this has caused a Ground Loop to be created.

I bought off eBay an RS232 opto isolator thinking this would cure it, unfortunately this stopped HRD communicating with the radio so I was stuck! posting the problem on the Yahoo Group forum came up with the answer.

The simple answer from Dave (G4UGM) was not to connect the Serial  pin 5 Ground wire making sure the outer shells of the D9 Socket & Plug were connected, and this did the trick.

(Scroll down for update)

The Serial connections on the Kenwood TS2000 are:

1- Not connected

2- RXD

3- TXD

4- Not connected

5- GND (did not use)

6- Not connected

7- RTS

8- CTS

9- Not connected

The finished unit with pin 5 disconnected goes in the back of the radio, the male and female connectors were soldered back to back, pin for pin except the break of Pin 5  –

29 September 2015     ***UPDATE***

Not sure what changed, but the mains hum came back!!, knowing that a 3 wire opto-isolator didn’t work, I bought an 8 wire opto-isolator from Tronicore, this comes complete with serial leads and a 12vDC PSU (American Power Plug).

I powered the unit from my rig supply, so didn’t use the PSU which came with it, the only other thing I needed was a 9 pin gender changer (Female to Male) to connect to the serial port on my PC.

The interface only works one way round so watch for that, mains hum has gone 🙂