[Elecraft] KPA500 TX with second radio SOLVED

[Andy Durbin]

"Chuck keeps providing riddles for behavior that is a bit different than what I expected. The original K3 with the KIO3 board exhibits exactly the behavior I outlined previously. A K3S or K3 with the KIO3B interface behaves the way Chuck describes. A look at the KIO3B schematic reveals why - it has series connected diodes in the band pull-ups so that when the main Vcc drops at power-off, the band lines are disconnected from the power rail. Thus the pull-ups inside the KPA500 take over and it sees the magic 1111 pattern indicating that no band is connected."

Perhaps I'm a bit perverse but  that provided some amusement.

73,
Andy, k3wyc