[Elecraft] N6XI NAQP RTTY July, 2007 with K3

[Lyle Johnson]

> From my perspective, those keying circuits want to be inside the radio, 
> safe from harm. Is there any reason why they weren't made part of the 
> radio - or why I shouldn't put them in when I get my K3? (Assuming of 
> course I can get into that part to do so...)

The K3 accepts open collector(or open drain) to ground as inputs, or can 
be driven with 0 <= x <= +5 volts.

Some stations use RS232 levels (which can be as high as +/- 25V) for 
direct FSK.  Such levels need to be converted to 5 volts for the K3 
digital inputs.  Further, RS232 specifies a "1" as -3 < x < -25V and a 
"0" as +3 < x < +25V, so a polarity inversion (in hardware or software) 
is also required.

73,

Lyle kK7P