Hello Jan,

The problem seems to be worse when I am out in the field. When I am in house the problem is nonexistence. There is only one wire from the collector to the zero keyboard switch, which is only about three inches long. It was routed the most direct path with any consideration of what was around it. The wire is # 40 gauge. There is a 0.1uf cap across the collector and emitter of the NPN transistor but I don't think that is doing anything.

You are right about the amount of interference this phone makes. When I put it next to the speakers (about 18 inches away) on my computer you can hear lots of RF chatter.

The DTC4 (newer models) phones generate a lot of interface compared to the DTC3 (older) phones. This same experiment on an older DTC3 phone works without any problems.

The question is how to get rid of this possible EMI?

The emitter is grounded to the shielding inside of the phone. I might try running two wires twisted to the Keyboard 0 key hoping the twisted pair will eleminate the possible EMI. One wire will go to one side of the switch and the other wire will go across the other side of the switch. Will let you know the results later.

Regards,

Charles Bannister