Please describe the aux cables you have in use between the equipment. It is highly unusual for the BCD lines to change state during transmission, on any other time without actually changing the band on the K3. If you are using very long Aux cables, or have other equipment connected to the cable (that uses the Band lines), it could account for issues. There is at least one band decoder kit on the market that uses poorly designed receivers that will adversely affect the band lines in a K3 or K4 system to the point that the KPA receives incorrect band indication.
Are you directly monitoring the band lines with an external indicator? If so, please describe the indicator. The KPA _will_ change bands due to a signal on another band (such as a harmonic). We have not seen that to this point with K3 or K4, but it is certainly possible. Not that the RF signal count always overrides the band signals - it counts the strongest signal at its input. This situation may be due to RFI, but I am suspecting something else at present, such as very long AuxBus cables or an issue in the system. Any further info you can provide would be very helpful - is there another transmitter near by, or anything else that may be injecting alternate signals into the amplifier (usually on the xcvr input side, but if strong enough it could come in through the antenna). Note that a very strong signal coming into the antenna port would also affect the SWR calculations and display. Something is going on, but it may surprise you when you discover it. 73, Jack, W6FB > On Jan 12, 2024, at 2:18 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 jackbrin...@me.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 arch...@mail-archive.com
