Author Topic: Cylindrical cavity resonator for Oscillator  (Read 456 times)

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Offline TheUnnamedNewbie

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Cylindrical cavity resonator for Oscillator
« on: May 31, 2020, 11:54:41 am »
I want to make an oscillator using a cylindrical cavity as resonant element. Anyone have any pointers on how to start this? I want to use en existing cavity (a drinks can) as this is to be a kind of 'RF/electrical engineering magic demonstrator' for educational purposes.
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Offline retrolefty

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Re: Cylindrical cavity resonator for Oscillator
« Reply #1 on: May 31, 2020, 12:02:54 pm »
It would be helpful to know the operating frequency you would like to demonstrate at. VHF needs much larger size then UHF.

 

Offline TheUnnamedNewbie

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Re: Cylindrical cavity resonator for Oscillator
« Reply #2 on: May 31, 2020, 01:00:41 pm »
As I already stated, I will be using a drinks can as resonator. These have a dimension of about 66mm x 115 mm.
After some research I've found that this should have a resonant mode around 2.6 GHz, which is what I will start my idea on. I will do some simulation to figure out more of what is going on, but was hoping I could get some tips as to feeding structures or how to optimally do this (EG, is it best to use 1-port impedance as resonant tank, or use 2-port resonace as feedback network?)
The best part about magic is when it stops being magic and becomes science instead

"There was no road, but the people walked on it, and the road came to be, and the people followed it, for the road took the path of least resistance"
 

Offline RoGeorge

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Re: Cylindrical cavity resonator for Oscillator
« Reply #3 on: May 31, 2020, 01:36:40 pm »
From Google, not exactly an oscillator, but has plenty of cylindrical cavity:
https://pdfs.semanticscholar.org/56a0/6962022a7d2b17414f52180440f96308f2d7.pdf
 
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Online CaptDon

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Re: Cylindrical cavity resonator for Oscillator
« Reply #4 on: June 02, 2020, 01:46:23 am »
2.6 gig sounds very high for that dimension. I have seen
old WWII cavity resonators with a 2C40 lighthouse triode
smaller than your can and resonant around 1.1 gig. The
size of the can seems like an old 450mhz band pass filter.
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Offline geggi1

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Re: Cylindrical cavity resonator for Oscillator
« Reply #5 on: June 10, 2020, 02:16:02 pm »
Have a look at this one.
http://85.226.112.143/use/resonator_1.htm
As the feirst resonance is at 1/4 wave lenght your first resonance will be in the area of about 652Mhz [ 300/(4*0,115)] but there can be harmonics at other ferquencies typical 3rd (1956Mhz) and 5th (3260Mhz).
To get a resonance in the 2,6 Ghz area your resonating pin must be about 28mm.
The calculation you have done is for a full wavelength resonator that  is the 4th harmonic. You will get your first harmonic on 1/4wl. normaly the 4th harmonic has a lower value. The most dominant is normaly the odd order 1th, 3rd, 5th, 7th.

https://www.ahsystems.com/EMC-formulas-equations/frequency-wavelength-calculator.php


I did a test of rezonanse wit a T-connector, 0,5l drink can (abt. 200mm hight), a 150mm teflon coated wire and the DSA815TG and found a sharp resonanse at 390Mhz or there about. It is some time ago and I can not remember the exsact lenghts.
 


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