[Elecraft] USB/3.5mm Extension?

[Jack Brindle]

Andy’s point that the KXUSB actually has 0 to 5V output on its TxD line is correct. This is most likely the limiter in how long of a cable you can have between the KXUSB and the KAT500.
The actual length is probably best derived by trial and error. As K9YC points out, the rise and fall times of the signals will be the limiting factor, and will actually determine the
maximum length. The rise and fall times need to be pretty short due to the data rate used by the KAT500 (38400 bps).

As an educated guess, I would suspect that an extension of 5 or maybe even 10 feet should work, depending on the cable capacitance. If you see any strangeness to the communications, use a shorter cable.

One other thing - Andy is a good friend, someone with whom I enjoy having deep technical discussions. We learn a lot from each other, and he contributes quite a bit to the
technical nature of the list. His presence here is very much welcome.

73,
Jack, W6FB


> On Nov 28, 2023, at 10:14 AM, Andy Durbin <a.durbin at msn.com> wrote:
> 
> "Indeed, it is NOT true that the KAT500 uses TTL signal levels for the serial port. "
> 
> Ah, but I said "Isn't it true that the KAT500 USB cable uses RS-232 protocol but TTL signal levels? "   Perhaps I should have been more specific.  My recollection is that the USB/Serial cable transmits a TTL signal.  I have no way to know the receiver characteristics of that interface dongle.  I did study the KAT500 I/O schematic to understand that end of the connection.
> 
> Anyway, not posting to "keep you on your toes".  I was confused by this interface when I first decided to work with it so didn't want people to assume it was RS-232 compliant.
> 
> 73,
> Andy, k3wyc