Before replacing cables or adding ferrites, I would make sure that all the chassis are bonded together with short runs of heavy gauge wire. Differences in ground potentials between equipment can make a mess of things.
For more info, get the book on grounding and bonding from the ARRL. https://www.arrl.org/grounding-and-bonding-for-the-amateur wunder K6WRU Walter Underwood CM87wj http://observer.wunderwood.org/ (my blog) > On Jan 12, 2024, at 12:18 PM, Jeff Wandling <j...@w7brs.com> wrote: > > Dear Elecraft aficionados: > > The symptom is KPA switching bands during Tx. > > Seems like a while ago I was troubleshooting the RFI problem between the > equipment. > > K3 + KPA500 + KAT500 > > Using the "enhanced" configuration where serial cable between the K3 to KAT > to KPA assisted in communicating band changes as well as key-down event and > so on. > > I own two KPA-500's. Both are less than 6mo old. > > Let me refer to them as KPA-1 and KPA-2. KPA-1 is in the hands of Elecraft > for repair. It worked flawlessly (until needing repair), but the RFI issue I > will write about did not exist when that KPA-1 was in the chain. > > KPA-2 was purchased in December as a backup. Since putting KPA-2 in-line, the > RFI problems I will describe have gone unresolved. > > Scenario is with KPA-2 in-line. > > Even running tiny power (< 10W, <15 W) I can routinely and 100% reproduce the > problem where the BCD data in the AUX line that carries the information about > which band the KPA should be set on will change during Tx. > > For example I can put KAT into MAN, put KPA in bypass. Tune the antenna via > K3 and witness the search resolve to a 1:1 on the SWR. That sometimes will > trigger the effect -- I can see in the KPA, even in bypass that the band the > KPA is set on is changed from the band the K3 is set on. Even more insidious > is that if the KPA winds up on a different band after the tune (or after > "VVV" CW testing after tune), that pressing the band button on the KPA to > bring it back does not bring the KPA back to the right band. It is as if the > KPA has two states of band-awareness.. The awareness of the band displayed in > the LCD and the band that the input is set for. > > Here's an example: > K3 on 40m > Tune per usual (KAT MANUAL, KPA Bypass) > KPA remains on 40m. > K3 power output 14W > Then put the KPA into Operate > Tap "VVV" out on the key. > Witness the KPA operate but then switch band to 30m or 17m or 20m, etc.. (not > expected) > Then on the KPA tap (Band) 7 (for the 40m band) and nothing happens (not > expected) > Tap on the KPA 14 then the whole chain switches to 20m (expected) > > Suppose the TUNE did not yield a band-switch during Tx, repeating the test > but this time putting the KPA into Operate after the tune is sure-fire going > to cause the bandswitch. > > (I configured the KPA to go to Bypass in the event of a band-change event in > order to have some sense of protection while the key-down test Tx occurs). > > That's the scenario where after Tx the KPA is out of sync with the K3. > Whether or not the KPA is attempting to frequency-count is not evident, the > KPA:RADIO setting is "K3" which means leverage the BCD data from the K3 > vis-a-vis the KAT path. > > I can replicate this band-inconsistency at will. I don't think I can safely > operate the equipment if the BCD encoded band data is fluctuating during Tx. > What would happen if I switched bands (N1MM) and hit the keyer and the KPA > got confused on the last Tx? Magic smoke I imagine. > > Only happened with KPA-2 not KPA-1. But I'm wondering if KPA-1 suffered a > catastrophe caused by this scenario and I didn't notice the clicking > band-switch because I had not expected it to switch bands during Tx. > > What have I done to remedy? I think I've tried everything but obviously I > have a gap -- otherwise I'd have solved this problem. > > - New coax between everything. > - Shorter or longer coax, different coax (RG-213, 8X, LMR-240, etc..) > - Tighter loops (6 -8") when there is excess coax or lazy big loops where > there is excess coax. > - New connectors/adapters (Yes, Amphenol) > - Re-route coax different ways. Avoid this, that and the other, etc.. > Permutations of routing. > - Move and adjust placement of equipment. KAT near the KPA, KAT away from the > KPA, both near or away from the K3, etc.. > - Chokes between things. K3 to KPA, KPA to KAT, KAT to antenna system > - Non-bleeding chokes, bleeding chokes. > - Ferrite on serial cables, more ferrite, insane amounts of ferrite, or zero > ferrite > - Move the position of serial cables above, below, up, down, left, right. > > I haven't got to the point of putting little tangerines on altars and burning > incense. I'm trying to keep a positive mood while part of me wants to take up > the art of Bonsai and raking the sand. > > Obviously RFI is a likely culprit, but I'll be damned if I can figure out > where it is -- or rather why it would be -- affecting this given all of the > mitigations attempted. > > But I'm always a student and looking for things that were/are not obvious at > first. > > I'm almost to the point where I will take away the "enhanced" mode serial > data path between the equipment and rely on the analog key-line between them > and RF frequency-counter capabilities so that the KAT and the KPA are on the > right band when I key-down. I just need to review the docs to make sure I > have the KPA and the KAT setup to go "analog" rather than "KPA:RADIO = K3" > mode. > > But the 'enhanced' mode is much more preferred since it is a K-line. > > Thoughts and suggestions welcome. Ping directly if you wish. > > Thanks! > > Jeff > > --- > 73, Jeff W7BRS > https://blog.w7brs.com > ______________________________________________________________ > 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 > Message delivered to wun...@wunderwood.org ______________________________________________________________ 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 Message delivered to arch...@mail-archive.com
