Thanks Don. Mike W0MU
J6/W0MU November 21 - December 1 2011 CQ WW DX CW W0MU-1 CC Cluster w0mu.net On 10/11/2011 11:27 PM, Don Wilhelm wrote: > Mike, > > Your band decoder is apparently loading down the K3 band data lines to > the point where they cannot be unambiguously decoded by the KPA500. > Yes, less than 3 volts on the band data lines is in the "noise region" > for digital logic. > > You may have to add isolation diodes and pullup resistors in your band > decoder to solve the problem. > > It is true that the K3 has pullup resistors, but they can only supply so > much current. Apparently, your band decoder requires more current than > the K3 pullup resistors can provide. > > The solution is to add a diode at the band decoder Band 0-3 lines. The > cathode should point toward the K3. Then on the anode side of the > diodes, add a pullup resistor to whatever voltage is required by your > band decoder. > > The early K3s "did it right" in providing open drain outputs for the > band data lines, relying on the attached device to provide the pullup > resistors. BUT, many devices do not provide those pullup resistors - > many radios have the pullups at the driver end rather than following the > normal rules for logic circuits which place the pullups at the > receiver. SO, the K3 added pullup resistors at the drivers. > NEXT, enter the KPA500, which now needed to provide protection for > itself from band decoders which DO provide pullup resistors (but to a > voltage higher than 5 volts), so the KPA500 added isolation diodes and > its own pullup resistors to the band data lines. That then requires > that the high level for the band data lines be a diode drop level above > the normal high logic level. No problem if only the K3 and KPA500 are > connected, but if a band decoder that takes current in the high level > state is connected, the K3 will not supply enough current from its > pullup resistors to bring the high logic level to an unambiguous (to the > logic devices) high level. In other words, the band decoder you have > chosen is sucking too much current from the K3 when the band decode > lines are in a high logic level state. The addition of diodes on the 4 > band data lines (cathodes pointing toward the K3) is the only solution, > and then you will have to add pullup resistors on the anode side of the > diodes to assure (to the band decoder) that the high levels are properly > detected. > > Bottom line - the K3 original design "did it right", but caved in to > popular demand because many band decoders did not "do it right". Then > the KPA500 had to contend with devices that "did it right", but at > higher voltages than the KPA500 could tolerate - so we are back to the > original "question" of where the proper place for the band data pullup > resistors should be. I am sorry to say that it is quite a mixed bag of > confusion since one band decoder does it this way, and another does it > that way. Right now, the only sensible solution is to add the > protection diodes and pullup resistors to each band decoder that is > attached to the K3 and KPA500 combination. > > 73, > Don W3FPR > > > > On 10/11/2011 11:08 PM, W0MU Mike Fatchett wrote: >> I am attempting to hook up an Array Solutions DBS-2 Band decoder on the >> K3. When I have it connected using a Y cable the KPA-500 no longer >> follows the bands it seems to get confused. I have the KIO rev B board >> which I believe should have the pull up resistors but I am seeing 2.3 to >> 2.5 volts on the Band out pins. I think this should be between 3-5 >> volts. Are there KIO rev B boards that might not have been upgraded? >> SN on this K3 is 2745. >> > ______________________________________________________________ > Elecraft mailing list > Home: http://mailman.qth.net/mailman/listinfo/elecraft > Help: http://mailman.qth.net/mmfaq.htm > Post: mailto:[email protected] > > This list hosted by: http://www.qsl.net > Please help support this email list: http://www.qsl.net/donate.html ______________________________________________________________ Elecraft mailing list Home: http://mailman.qth.net/mailman/listinfo/elecraft Help: http://mailman.qth.net/mmfaq.htm Post: mailto:[email protected] This list hosted by: http://www.qsl.net Please help support this email list: http://www.qsl.net/donate.html
