Re: QCX 40 - Need help with BPF alignment

Alan de G1FXB

Hi John,

Something to bear in-mind I'm doing this blind as I have not built a QCX,
people who have, need to correct my statements if wrong!

C1 seems OK.
TX Power OK.

Overall the peaks seem low, past discussions have indicated people report scaling factors of 8/9, but as you say its dependant on AF gain position for all but C1 alignment.
There is a voltage table at the end of the Assembly Manual, section 6.4
The measurements were made using the QCX inbuilt DVM which has a lower I/P impedance than most stand alone meters.
At first sight the table is a little strange because it doesn't start at IC1 but the order it is made, sets the basic requirements and then follows the signal path through the different circuits.
For sake of convenience it would be best to use the inbuilt, unless you have any concerns to its accuracy.
Oscilloscope trace & levels can be found on the troubleshooting web page. If you have access to a scope, through a friend if necessary.

A quick bit of background,
What version kit have you, Firmware revision?
The kit otherwise went together OK and raised no queries?
If possible a couple of photo's of top & bottom of the PCB just incase it's possible to spot something.


On 09/08/2018 21:26, jmcf2005@... wrote:

Hi Alan,

Thank you for your help. Following your suggestions, here’s what I found;

  1. I checked the continuity of all the windings on T1, as well as L1, L2, L3 and L4. All were good.

  2. I checked the Peak BPF and while adjusting it noted that with C1 fully meshed, the maximum amplitude was 4, with 6 large segment bars on the scale. As I rotated C1 to fully open, the number of bars increased from 6 to 13. It didn’t look like a sudden jump.

  3. I then checked the phase adjustments with the volume set at about 50%.

I-Q Balance was an amplitude of 6 with 50% of the bars

Phase Lo was 5 with 50% of the bars.

Phase Hi was 6 with 50% of the bars.

I checked the transmit power with a meter into the dummy load and it was exactly 4w.

You also mentioned doing voltage checks. Are there any instructions somewhere on the procedure for that?

Thanks again.




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