Hi all,
here are my test results and the pleasant final results from the working QMX (20 m - 10 m).
I've made some steps.
1. Checking the uncertainty of measured values for L
I have a set of filter elements to build a high band QDX. I wound some toroids T37-10 following the QDX manual. The measured L were between 10 % and 15 % higher than expected. Maybe I've measured a little bit more than the real value but not 25 % or more like for my T30-17.
2. Checking the validity of values from build LPF
I used a tiny rf test board to build LPF. First I've build the filters from the parts for QDX.
Measurement was done by a VNWA looking at the attenuation at the band frequencies and the first and second harmonic and the match toward the PA.
The measured values were fine. So the setup should be usable.
3. Checking the LPF for QMX
I've build the LPF using the elements for my QMX (again on the tiny test board). The toroids were wound following the manual (L 508 with 11 turns). Measurement was done like in step 2.
LPF 20 m: values usable
LPF 17 m and 15 m: values not good
LPF 12 m and 10 m: values usable
To consider the capacity of the real TX (stray capacity of PCB and capacity from the PA) I've added some 10 pF to the capacitor toward the PA. Here are the results:
LPF 17 m and 15 m: values useable for 17 m and maybe for 15 m
Now I've reduced L 512 also to 11 turns.
LPF 17 m and 15 m: nearly perfect
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3. Building the QMX following the manual but L 512 with 11 turns, measured output and harmonics
The harmonics were measured using a precise SDR and a spectrum analyzer software. QMX and SDR were coupled with attenuators with an optimized value of attenuation.
The output was 4 … 5 W so ok.
The harmonics suppression was at least 56 dB so more than ok.
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Finally conclusion: following the manual would be ok, maybe also without the reduction for L 512.
This matches to what Hans wrote in this and in a different thread.
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73 and wish you success with your QMX
Ludwig
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