Re: Some measurements by DG8SAQ VNWA 3

AA7US
 

Adam,

Thank you for the reply.

OK, let me see if I have everything correct...

KN-Q7A and CS-Series DIY7 Filter General Rules
1. Decreasing DIY7 inductance value increases resonant frequency
2. Increasing DIY7 inductance value decreases resonant frequency
3. Lowering DIY7 adjusting slug position decreases inductance and increases resonant frequency
4. Raising DIY7 adjusting slug position increases inductance and decreases resonant frequency
5. Decreasing end capacitance values increases resonant frequency and increases insertion loss
6. Increasing end capacitance values decreases resonant frequency and decreases insertion loss
7. Decreasing center capacitor value decreases bandwidth and increases insertion loss
8. Increasing center capacitor value increases bandwidth and decreases insertion loss

Please let me know if anything is wrong with the above.

I'm finding out that trying to properly evaluate DIY7 filters using a signal generator and oscilloscope doesn't work perfectly because the added capacitance of the test leads affects the filter's characteristics.  I guess a spectrum analyzer and tracking generator would be needed to do it correctly!

73,

John
AA7US

---In CHINA_QRP@..., <rongxh@...> wrote :

John,

Although I haven't tested the BPF for CS-Series due to impedance mismatch, I can try to answer your questions:

1. The resonating frequency will be a bit lower (so you will need to tune the slug higher position to tune the frequency back) and the insertion loss will be smaller (but smaller insertion loss is not aways good if the overall gain is enough, instead, sometimes selectivity is more of a concern) if you increase the value of capacitors.

2. Same as my finding in my measurements. The bigger value, the less insertion loss, but a bit wider bandwidth. It varies with band and impedance but generally it is this trend.

3. No modification is required for 15 meter band.

Thanks,
Adam

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