[Elecraft] Re: N6XI NAQP RTTY July, 2007 with K3

[Don Wilhelm]

Wayne,

You might want to bump up that parts count to 3 - and add a diode from 
the base to the emitter of that transistor (cathode toward the base) - 
protects the transistor from damage on the most negative excursion of 
the RS232 signal line which can go to 25 volts negative by the RS232 spec.

There is not likely to be a problem when driving from a PC serial port 
because the PC usually does not drive that far negative, but just the 
same, I like to have things that work over the full range of the spec 
rather than work in most situations.

73,
Don W3FPR

wayne burdick wrote:
> Jeff,
> 
> The K3's I/O module already provides for the use of RTS or DTR for PTT 
> and/or CW KEY in (two separate control lines). The exception is FSK, 
> which is on the ACC connector. In the present incarnation, driving this 
> line from a PC requires two external parts (one garden-variety NPN 
> transistor and one resistor). I used MMTTY with this interface during 
> NAQP this weekend.
>