[Elecraft] [K3] Built in USB interface for K3

[Lyle Johnson]

>
> Obviously a possibility here for Elecraft to offer the KIO3 in either 
> version (RS-232 or USB connector) as an ordering option, if they've a mind 
> to...

There are a few issues here:

1) Does the internal RS232 charge pump have harmonics in any Amateur 
bands?  Are they audible?

In the KIO3 we took great pains to not use a charge pump based RS232 
level shifter since this circuitry is extremely close to the KXV3(A) 
which may carry the Rx Antenna path.  Instead, we created a clean 
oscillator at audio and derived the necessary negative bias voltages 
from it.

The RS232 interface is also right next to the KRX3 SubReceiver antenna 
input.  One must be very careful about noise management here -- or go to 
use of castings and lots of internal shields like some radios use.

2) For an internal USB interface, we'd like to see Rx Audio (stereo) and 
Tx audio, along with FSK, in a way that requires no special drivers for 
most computers running most current or recent OSes.  This reduces 
cabling requirements.  Conceptually, think of a microHAM device (or 
Navigator, RigExpert Plus, ...) internal to the radio.

3) For the present configuration, you need a cable between the K3's 
RS232 port and the computer.   Changing to an internal USB<->RS232 
adapter does not reduce or simplify cabling requirements, and in fact 
reduces the flexibility of the radio's interface!

4) Some products, like the P3, interpose themselves into the RS232 
control path in a daisy-chain fashion.  If the RS232 is changed to USB 
on the K3, the interposing device either needs to become a USB host 
(perhaps USB-OTG is sufficient) or an intelligent "bridge" device.  This 
is far more complex and potentially much more costly than the present 
solution.  Again, the RS232 interface appears to be the better choice at 
present.

Enjoy!

73,

Lyle KK7P