Question about resistors and capacitors in a circuit

[XuFyaN]

in this circuit I've found out the function of every component except R4, R5 and C4,C7 and C8 ...
can anybody please explain the purpose of R4, R5 and C4,C7 and C8 ?

[PLAIN]http://www.2electronic.com/wp-content/uploads/2010/03/cellphone-detector.jpg

also the Capacitor C5 (47pF) is connected across pin 8 and ‘null’ inputs (pin 1) of IC1 for phase compensation and gain control to optimize the frequency response,
what does it mean by phase compensation ? and why the collector is connected with R4 and C7 ?

and what will be the effect on circuit if i remove C5 or C2 from it ??

 

[willem2]

I don't really know what the left side of the circuit does. C1 and C3 seem to form a potential divider that will throw away 999999/1000000 of the input signal. (since the non-inverting input of the opamp sits at 0.52 V.

R4 however is the collector resistance of a common emittor amplifier, and also is needed to limit the current through the led.

C7 and R5 will limit the time that the trigger input of the timer keeps a low voltage, since the timer won't start until this input is high again.

What kind of signal is this circuit supposeed to receive?

 

[XuFyaN]

the circuit is sensing the frequency radiation of mobile phone through C3 (as mentioned in report)
actually C3 is acting as an antenna you said C3 is used as potential divider ?
and capacitor C5 is connected across pin 8 and ‘null’ inputs (pin 1) of IC1 , i don't know the reason :S why it is connected there :S

 

[vk6kro]

From a data sheet the CA3130 has a maximum frequency of 15 MHz and in this circuit it would be a lot less than that.
You can get a data sheet here:
http://www.datasheetcatalog.org/datasheet/intersil/fn817.pdf

If you look at the input of this chip here:[PLAIN]http://dl.dropbox.com/u/4222062/CA3130.PNG

You can see some diodes at the input that may function as rectifiers at 900 - 5000 MHz which is the sort of frequency used by cell phones. This might give you some signal reception at very close distances.

The 555 here is used as a monostable. If its input is pulled low, the output will go high and produce sound from the buzzer for a time determined by R6 and C9.