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 arch...@mail-archive.com
