[Elecraft] USB/3.5mm Extension?

[Jack Brindle]

Andy, you do a great job of keeping me on my toes. But...

Indeed, it is NOT true that the KAT500 uses TTL signal levels for the serial port. The KAT500 has voltage translation circuitry that allows for the use of quasi-RS232 signal levels.
Quasi? Yes, the transmit data goes to +12 Volts, but it only goes down to chassis ground levels. This actually gets the RS-232 specification which has a transition band in the 1-2 volt range.
The receive circuitry is fully capable of translating RS-232 signal levels to the +5, ground levels used internally to the KAT500. Note that the KAT500 can receive TTL-level signals, but it does not drive them.

What this means is that if you were to drive TTL chips directly from the KAT500’s data port you would probably have to replace a lot of those chips until you realize they cannot withstand the +12V on their inputs.

So yes, the extension cable may be used. Just don’t use a high-capacitance cable (which usually means a very long one), as the KAT may not be able to  drive the load on the far end.

73,
Jack, W6FB

> On Nov 28, 2023, at 8:46 AM, Andy Durbin <a.durbin at msn.com> wrote:
> 
> "Yes. At the point for the extension, the signals are RS-232, not USB. You should be able to use a much longer cable if need-be."
> 
> Isn't it true that the KAT500 USB cable uses RS-232 protocol but TTL signal levels?  TTL may not be as tolerant of length extension as true RS-232.   Certainly no problem with about 10 ft extension though as my KAT500 USB/Serial extension is close to that long when my KAT500 is connected to the PC .
> 
> The KAT500 PC interface is a bit unusual as it seems to be designed to use TLL but also accepts true RS-232 levels with no problem.   A true RS-232 receiver may not operate with a single ended TTL input.  RS-232 signals swing positive and negative and are only zero volts when the driver is not powered.  TTL swings between 0 V and 5 V.  RS-232 compliant transmitters are also required to tolerate continuous short circuit without damage.
> 
> Elecraft was careful not to describe the KAT500 PC port, or the USB cable, as RS-232.
> 
> These details will only be of interest to anyone considering making a device that interfaces directly with KAT500.
> 
> 73,
> Andy, k3wyc
> ______________________________________________________________
> Elecraft mailing list
> Home: http://mailman.qth.net/mailman/listinfo/elecraft
> Help: http://mailman.qth.net/mmfaq.htm
> Post: mailto:Elecraft at mailman.qth.net
> 
> This list hosted by: http://www.qsl.net
> Please help support this email list: http://www.qsl.net/donate.html
> Message delivered to jackbrindle at me.com