Cavity Filter Basics

#227 In this video I look at another constructive type of filters that moves from the world of lumped elements to the world of distributed elements, what I'm referring to is cavity filters. I look at some of the basic operating principles as well as some constructive types and next time I will be performing some measurements on a set of practical devices.

Filter series:

Further reading:

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[jonathanlister]

Excellent and elegant as always. This exemplifies the artiness of electronics!

[inrit]

I have been waiting for a clear and concise video on cavity filters forever! Thank you so much!!!

[trcwm]

Can’t wait for the practical measurements! 👍

[TheDiveO]

having seen this some time ago in one or some of Curious Marc's vids, this is finally building the missing link to this dark art of trolling the rest of electronics!

[electronics.unmessed]

Good explanation! Thanks for sharing! 👍

[fotografm]

Excellent video ! I appreciate your clear and thorough approach. This technology cannot be replaced by SDR when power is involved eg. in a transmitter. Keep up the good work !

[ThermalWorld_]

Thanks for explaining Cavity filters.. Very black magic 😛

[deang]

"I signed up to a degree in electronic engineering, NOT plumbing!"

[tomgburklin]

thank you, beyond my brain to absorb all of it ... right now. but gets me thinking. -

[estebhann]

How is it response against temperature? In case the filter is in a cabinet expose to direct sun, external temperature could range 20° differential in a night-day cicle. Is the resonant frequency affected and how much? Thanks.

[tr_sc]

I am a hobbyist and I experiment with RF, my mathematical knowledge is poor. I have a quartz oscillator ICD6233 programmed for 100MHz, but there are multiple harmonics and I need to boost the 400MHz while filtering out the rest. I need to also narrow the slopes of the frequency (in hobbyist terms) I need to suppress -filter out (attenuate) the grass (notch) before 400MHz and after it. Is it possible by using a cavity filter? I did experiment with LC Band pass filters shunt and series but I couldn't get the results I wanted. Can you suggest a solution? Thanks a lot.

[BartKus]

Any chance for FEM of these filters? Like, what's an optimal coupling loop shape / position? Some coupling loops use flat wire instead of round. Why?

[andrewmcfarland]

Can we see one of those nifty copper boxes on a VNA? 🙂

[StreakyP]

great video many thanks... talking about amateur radio "abuse" of these things I have heard of aluminium beer kegs successfully being used as the conductive "cavity" for a VHF filter but the best one was a April fools joke about a 30' shipping container for a 7MHz (40 metre) cavity filter.

[-Tris-]

And I still don't understand what's going on with the last filter I build. It was meant to be for 149 MHz but has a second dip at 137 MHz. Nice 2 meter bandpass, but that's not what I wanted.😅

[guytech]

I would have liked to see the design of those two sample filters you created. Design, construction, and testing. That would make a interesting video. For instance how did you spec out the size, positioning of the internal components & how to make any adjustments (presuming its possible with the construction method used.

[Kori]

I wish these videos better explained the design. I cannot tell what is grounded and what is not. Where does the center conductor and shield of my coax connect??

[joansola]

Super interesting as always. Question: the 50 ohm source impedance in the models should be in series no? Or what is the effect of having this resistor in parallel with the voltage source?

[byronwatkins]

The electric field is perpendicular to equipotentials (i.e. conductors). At 3:00, the electric field is radial rather than longitudinal.

[thePavuk]

"The way how Machine God speaks with you depends on size of scented candles and distance between them during the ritual."
- Tech-priest of Adeptus Mechanicus