I am sorry to report that I had to remove the converter from under the QCX PCB. The voltages looked clean on my oscilloscope but I could hear harmonics of the switching frequency every 58 kHz on 20m.

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Simply replace the existing 7805 with a Recom r-785.0-0.5. It's pin compatible and fits neatly where the 7805 was. Then reduce the the backlight supply current by changing R48 to 1.8 k (yep, seems hig

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Excellent example of home-brewing! Very nice, Helmut!

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OOOps, I forgot to mention that the 7805 and R48 (270 Ohm) are of course left out now!

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Another way to reduce current is change R48, that determines the backlight brightness Increasing it lower the brightness and the current. The stock 270 ohm is 37ma, increasing to 1000 ohms lowers it t

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Hi, I am using a battery of 12 cells in series giving 12 x 1.2 V = 14.4 V. The QCX needs 14.4 V for the analog circuitry and for the PA to provide an output of 4 W. The digital circuitry and the LCD u

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Hi, Reduce the battery pack to 10 cells and the current will be reduced as well as the voltage. Your output power will be reduced but not enough to make any practical performance changes beyond reduci

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Hi, I just added 1 uF to C6. At my QCX-20m, there was no noticeable increase of sensitivity. Checked this with low level noise source. 73 Axel, DF1ET

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Hi Hans :), Amazing what some real programming can do :). Lots of fun :).

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Very clever. Congratulations, it seems a rather ideal solution so long as the interupt doesn't create latency for some other item. Joe

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Hello Karlis, all I managed to solve the sidetone click by firmware alone... this article is now updated with 'scope screenshots: http://www.qrp-labs.com/qcx/qcxmods/sidetone.html#firmmod I am running

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Too late bro... I'm going to sleep now, to dream of abused PWMs and narrow slices of CPU time. And will have one more try in the morning... 73 Hans G0UPL

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I know the feeling when the solution seems just around the corner, but let me not take away your time from QSX :)

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Hello Karlis Yes, I tried various different things along these lines that you suggest. In the end after many hours I still couldn't make it work cleanly. It may be that some other interrupt with varia

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Hi Hans, I have an idea for the SIDETONE PWM signal, but it depends on how tight your timing/memory requirements are in your QCX code. You'd probably have to squeeze a high-frequency interrupt routine

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Hi Karlis, all I *almost* made the sidetone click improvement in firmware too! I tried to play with the PWM signal, by arranging for its duty cycle to be 50% but for there to still be a 700Hz frequenc

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I'm so happy now that I made the effort to do the FW updates in situ with the USBasp it will make upgrading the firmware a breeze. Thanks Hans for the continued improvements. Paul DJ0CU.

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Hello again Karlis Yes I did have the idea of a resistor too and I tried it. Both on the LCD_RS line and on the SDA signal to the Si5351A. On the RS line made no difference. On the SDA line, a small v

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Hi Steve Yes! Guido PE1NNZ told me! That's right, I remember now. Well it was a very good tip! While it was not directly the solution to the problem, it did point in the correct direction and so enabl

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Hans, It was Guido Pe1nnz who gave you the hint. Yours, sleepily enjoying a beer with Alan at Schipol prior to flying home, Steve G0XAR

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