Jim. Jack Brindle and I just had an off-list email exchange in which he did state that the conductor capacitance and resulting waveform distortion may be a factor.
I really don't know the relative conductor to shield capacitance of the 4 conductor cable may be, but common sense tells me that it is variable depending on which conductor you select - at least your implementation of CAT5 twisted pair provides consistency. As far as your "transmission line" suggestions go, I am going to go out on a limb and say that YES, the AUXBUS signalling is a transmission line when external to the K2 (even though it is uncontrolled). The fact is that it "floats around" inside the K2 to all the option processors and the KIO2, it is not treated as a transmission line, and level sensing at the receivers is sufficient. When one goes external with that signal, the conditions change - to get the signal from "here to there", it must appear on some sort of transmission line (the cables in the Elecraft KRC2, XVxxx transceivers, KPA100 for some examples) do constitute a transmission line whether that is intended or not - but bottom line, the receiver is an input to a CMOS firmware chip, and that input is level sensitive. While the drivers and receivers may not have been designed for a transmission line ( I believe they were not), they are acting as drivers and receivers on whatever transmission line is presented between them. Be careful - amateurs often think of transmission lines as coax and parallel lines to antennas, but the world of transmission lines is much greater then that. Given the characteristics of transmission lines regarding distortion of digital square wave signals, the receiver "interpretation" characteristics become important. I do not see exotic line drivers and line receivers in any Elecraft devices, and so the obvious conclusion is that the "receivers" are level driven. If the data pulse is distorted, the timing may be off, and if the levels are influenced by line capacitance, switching may not occur at all. In other words, Jack Brindle has tested the K2 AUXBUS up to 6 feet with the standard 4 conductor cable, and all seems to be in order. For those who would want to go beyond that length, a lot of careful observation for potential problem situations may be required - in other words, go ahead and try it - it may work in your setup. but I cannot provide any assurance that it will work at that length for all situations. I am am a retired IBM Assurance engineer whose business was testing that a product met specifications under all possible conditions. So I can say that it might work for you, but that is no proof that it will work in another controlled setting unless you provide detailed data (well beyond "it works") to me and the general Elecraft community. I have not personally tested the command/response timing, but I do reflect Jack's comments which I do consider as regsarding "good engineering practice". 73, Don W3FPR On 3/23/2012 8:01 PM, Jim Brown wrote: > On 3/23/2012 3:24 PM, Don Wilhelm wrote: >> I recall that 6 feet was >> considered an OK length because it had been tested - longer lengths had >> not been tested. >> Of course, this applies to the K2. The K3 may or may not be different. > Thanks Don. At the very least, if this is a critical issue it ought to > be tested and the results noted. There's also the issue of cable > capacitance, which can be a big deal for high speed lines that are not > impedance-matched (like RS232). CAT5 has a big advantage there too -- > it's pretty low capacitance as cables go. Perhaps Jack can tell us if > that circuit is impedance matched (that is, treated as a transmission > line). > > 73, Jim K9YC > ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:Elecraft@mailman.qth.net This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
