Does your automatic antenna switch use the Unified Microsystems BCD-10 or BCD-14 band decoders, or is your design similar to the 4O3A Antenna Genius?
These products all use opto-Isolators on the four Band Data lines in the AUX cable. Wiring this type of decoder in parallel with the K3/KAT500/KPA500 AUX cable via a 15-pin Y-cable or similar *will usually cause automatic band changes on the KPA500 to stop working*, until you disconnect the antenna switch's band decoder, or send some RF so that the KPA500 frequency counter takes over. Not cool. Opto-isolators draw too much current from the K3 ACC pins, leaving too little voltage for the KPA500's band decoder to track properly. This is no problem for the KPA1500, only the KPA500, with or without the KAT500. The solution I discovered was to connect four 4.7K pull-up resistors to 12V to each band data pin in the K3 ACC cable, assuming the band decoder in the antenna switch can handle 12V instead of 5V (most can). The KAT500 and KPA500 will have no problem with 12V on the band data lines. The Y-BOX v3.0 (not pictured on my website because I have not had time to update it) includes these four pull-up resistors. They can conveniently be wired internally to the band data pins, and band switching should work again when all the devices are connected in parallel to the K3 ACC via the Y-BOX. This assumes your KPA500 "RADIO" menu is set to "K3" or to "BCD" so it tracks properly when the automatic antenna switch is disconnected from the ACC/AUX cables. FYI, you can still tap the BAND buttons on the KPA500 to change bands on the K3, because that uses the AUXBUS line (ACC Pin 2), not the BAND DATA lines. Many folks may have never discovered this cool feature of the KPA500 and KPA1500. 73, Bob, N6TV https://bit.ly/Y-BOX On Fri, Apr 23, 2021 at 6:18 PM Joe K2UF <[email protected]> wrote: > I have my K3-KAT500-KPA500 working great. The amp is off to the left side > and I can't see the display easily. while working on building an auto > antenna switch I noticed that the band display on the amp does not synch > with the K3. It seems to be random. If I hit one dit on the key the amp > will synch the band with the K3. I am not sure if this has been working > like this right along and just did not notice. > > Any ideas guys. > > 73 Joe K2UF > ______________________________________________________________ > 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 > Message delivered to [email protected] > ______________________________________________________________ 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 Message delivered to [email protected]
