I have a Rev 2 QCX and am experiencing minor clicks on Tx/Rx change overs. I made all the Rev 3 mods after I purchased the kit.
I noticed the above issue since I also have a QCX+ (where the sidetone is very clean). There appears to be no clicks on the actual RF envelope.
Does the current firmware (1.07A) level fix any of the issues below? I read that some firmware changes fixed sidetone key clicks without having to change hardware.
Rev 4: (31-rOct-2018)
1) Changed C21 and C22 to 1uF (previously 10uF) to reduce click on Tx/Rx switchover
2) Kits shipped after 12-Apr-2019 changed R41 from 470 to 150 ohms; R42 from 1K to 1.2K; C31 from 1uF to 2.2uF; to improve key-shaping.
3) Kits shipped after 12-Apr-2019 also changed R21 from 7.5K to 10K to allow phase compensation for larger range of component tolerances.
Rev 5: (06-Jan-2020)
1) Removed components R49, R50 and C39; R53 changed from 1K to 3.3K; the components were not needed since AUDIO2 DC bias is 2.5V already
2) Added R49 (1K), R50 (270-ohm) and D7 (1N4148) which are to implement a serial port for the CAT control interface
73, Bernie, VE3FWF
(most typos in this message have been generated by highly sophisticated auto-correction software)