Modifications for Rev 2 board of QCX needed? #qcx #sidetone


 

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


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73, Bernie, VE3FWF
(most typos in this message have been generated by highly sophisticated auto-correction software)


 

Hans has answered my question off list.  I have asked his permission to post his reply


73, Bernie, VE3FWF
(most typos in this message have been generated by highly sophisticated auto-correction software)


 

 There were several firmware improvements over time, that improved (reduced) the transmit/receive changeover click. With 1.07a you get all those improvements. 
 
The only hardware change that reduced clicks was the C21 and C22 changing from 10uF to 1uF. 
 
I do recommend this change. We use 1uF ceramics (MLCC) in the QCX+ and QCX-mini kits but any types will be OK. Lower capacitance values would be OK too but that does increase the attenuation. The QCX has plenty of gain but I wouldn't go much below 1uF. For example 0.47uF would be not too bad if you don't have 1uF.
 
73 Hans G0UPL 

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73, Bernie, VE3FWF
(most typos in this message have been generated by highly sophisticated auto-correction software)