Q factor coaxial cable structure

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lambdaanttech

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Hi Everyone ,

I'm struggling how to calculate the Q factor of a coaxial structure .
I want to make a notch filter that attenuates a frequency (220MHz) with a 3dB bandwidth of 4 MHz .
The notch filter would be made very simple by using a quarter wave resonator and a T piece .
Simple coaxial cable doesn't work since it is to widebanded , therefore I wanted to calculate a coaxial structure with a very high Q factor .

According to this equations : https://www.rfcafe.com/references/electrical/coaxial-resonator.htm
I putted them into a spreadsheet but it doesn't looks right .

Can anyone help me further how to calculate a Q factor of a coaxial line and how to further calculate the bandwidth according to the Q factor .
Any tips and hints are welcome .

Thanks in advance !
Kenny
 

you will shortly find that, at the least, you will need a small value series capacitor, the coax line in a Tee junction, with the stub end shorted out half wave away, and another small value series capacitor. You adjust the two capacitor values until you have the right stopband width.
 

To get a 220 MHz notch with 1.5% bandwidth you need a Q factor of the resonator greater than about 2500, which is almost impossible to be done with standard coax cables.
You need a cavity notch, or a Heliax Notcher circuit as is described below:

**broken link removed**
 

ignore my first post, I had the topology wrong. Here is what u want, using RG214:



btw, that simulation is for a capacitor Q of 200
 
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