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QMX: C516 - C525 swapped value #qmx

 

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On the QMX rev.2 PCB, it appears that the values of C516 and C525 are swapped between the schematic and the manual.
I have run simulations and the values in the schematic seem to be better.
What do you think?
 

On 27/02/2024 15:45, jh4vaj wrote:
t appears that the values of C516 and C525 are swapped between the schematic and the manual.

"The current assembly manual is correct: C525 is 270pF and C516 is 180pF. "

Be careful, simulations must account for stray capacitances.

73 Alan G4ZFQ
 

Thank you very much for the information.
Now I can proceed with the assembly with peace of mind.
 

Since the topic is related to this LPF, I will continue this thread.
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I measured the L value of the LPF (using NanoVNA-H4) and it seems that the inductance is too big for the number of turns indicated in the assembly manual.
So I determined the number of turns for each L based on actual measurements.
I did not swap C516 and C525 (C516 is 270pF and C525 is 180pF).

As a result, I did not see a decrease in the transmission output power at 20m band.
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80m: 5.4W
40m: 4.5W
30m: 5.8W
20m: 4.7W
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I assembled the 9V version.
The 60m band is not available in Japan, so I did not measure in that band.
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Also, spurious seems to be sufficiently reduced on each band.
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I will summarize my number of turns. Would anyone like to try a follow-up test?



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And the details are posted on my blog (in Japanese).
 

I've also found some higher values measuring the L and made some tests for LPF with changed elements.
You may read here. My conclusions at the end of this thread.

73, Ludwig
 

Right-on about the circuit simulation to model filter performance. Even back in university it was practically impossible to get the exact same results on a multi-element filter build.

I had one prof who would knock down your grade if the measured filter curves did not match the model. I spent many a late night in the lab poking and prodding winding spacing. He really only looked at turns counts. I was tempted to build him one with Litz wire just to give him a fit, but i needed the good grade.
--
Tisha Hayes, AA4HA
 

Thank you.

I am not sure if I understood your statement correctly as the language barrier is high for me....
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  • L is the number of turns as instructed in the manual, the inductance will be higher than expected.
  • However, in the QMX assembly, the number of turns of L is as instructed in the manual with good results.

Is this correct understanding?
 

L is the formula symbol for the inductance.
Using the number of turns from the manual L seems to be to high for most of my toroids.
Building different LPF on a tiny rf testboard and using numbers of turns from the manual and optional reduced numbers I've found, the numbers from the manual are ok. Only for one toroid I took one turn less (see here.)

So at all using the numbers from the manual should be ok.

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