RC Low Pass Filter cutoff frequency question

[samy555]

From:
http://www.talkingelectronics.com/projects/27MHz Transmitters/27MHzLinks-1.html
The 27MHz Receiver:
broken link removed
We have two RC low pass filters:

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This is a 27MHz receiver. What relationship frequencies such as 5Hz and 3.3KHz with the circuit frequency?
If your answer that these values are not critical! Please give me a range of good values for cutoff freq.
Thank you very much

 

[Audioguru]

The filters are extremely simple with gradual slopes. Their filtering is good only at frequencies far from their cutoff frequency.
The 5Hz filter prevents motor noises from affecting the receiver. The cutoff frequency was selected to cut noises from the motor that was used. If your motor is extra noisy then you can use a lower cutoff frequency. The electrolytic capacitor is almost useless at 27MHz.
The 3.3kHz filter helps the supply voltage to the receiver to have good filtering and to be a low impedance at 27MHz. The range for its RC values is very wide.

The receiver uses only one transistor as a super-regenerative type which has very poor performance. Also it actually transmits a 27MHz signal that causes interference with other radios on its frequency.

 

[samy555]

The filters are extremely simple with gradual slopes. Their filtering is good only at frequencies far from their cutoff frequency.
The 5Hz filter prevents motor noises from affecting the receiver. The cutoff frequency was selected to cut noises from the motor that was used. If your motor is extra noisy then you can use a lower cutoff frequency. The electrolytic capacitor is almost useless at 27MHz.

This part is excellent and I understood perfectly thank you.

The 3.3kHz filter helps the supply voltage to the receiver to have good filtering and to be a low impedance at 27MHz. The range for its RC values is very wide.

This part I did not understand anything.

 

[Audioguru]

The receiver transistor needs a very low impedance power supply so that its supply voltage is not jumping around by other circuits powered by it and so that its voltage is not jumping up and down with the 27MHz frequency. At the 3.3kHz cutoff frequency the 22nF capacitor has the same reactance as the 2.2k resistor. Then at 27MHz the reactance of the capacitor is only 0.27 ohms which is a very low impedance.

 

[samy555]

The receiver transistor needs a very low impedance power supply so that its supply voltage is not jumping around by other circuits powered by it and so that its voltage is not jumping up and down with the 27MHz frequency. At the 3.3kHz cutoff frequency the 22nF capacitor has the same reactance as the 2.2k resistor. Then at 27MHz the reactance of the capacitor is only 0.27 ohms which is a very low impedance.

OK
thank you guru
I highly valuable this remarkable effort