[Elecraft] HP48GX to KIO2

[rlewis@staffnet.com]

In the RS-232 specification there is Data Terminal Equipment (DTE - the computer terminal) and Data Communications Equipment (DCE - the modem). The transmit and receive data and various handshake signals are assigned to opposite pins so that the typical connection from a DTE to a DCE can use a straight through 1 to 1 cable (pin-1 to pin-1, pin-2 to pin-2, etc). If you want to connect a DTE to another DTE (computer to computer) then you needed a "null modem" cable. The cable reversed the connections so that for example, the transmit data from one terminal is connected to the received data of the other terminal. The cable looks to the terminals like a modem therefore it was called a "null modem" cable.

The difficulty with the K2 is that the "D" connector contains a number of signals and voltages that are not related to the serial communications. If you connect anything other than a custom made cable, you risk shorting one of these and damaging the K2 or sending a voltage to a computer that will damage the serial port on the computer. It was a poor choice in connectors in my opinion, but it is done now and you just have to be careful what you connect to it.

Elecraft is not alone in this, by the way. I have some equipment at work where the mfg has added "special" signals to the "D" connector because it was convenient at the time. I now have to deal with users running down to Radio Shack and picking up a cable that "fits" the connectors okay but does not function properly.