Hi,can any one help me...to determine the frequency my mobile is using for sending or receiving calls...??I want to implement cell phone detector...for that i want to my phones frequency so that i can tune my circuit to that frequency..

 

Hello,

The frequency band used are dependened on your location.
The wiki shows some:
https://en.wikipedia.org/wiki/GSM_frequency_bands

Bertus

 

Hi Harika,

In India the bands are as follows:

CDMA - 800 MHz
GSM - 900 MHz, 1800 MHz.

Regards,

Nandu.

and 2100 MHz for 3G

 

Was there a particular reason you asked this question? The reason I ask is that building a detector for these frequencies is a non-trivial undertaking. Most cellphones use digital modulation and the signal levels are much lower and harder to detect than the old analog phones. Maybe you were going to use a preassembled module for this project?

 

Actually, detecting the presence of a cell phone can be very simple - just a broadband diode detector can be enough. If you want to demodulate the signal...then yes, it can become a very involved project.

 

These days if you can see people, you can infer the presence of cellphones. So a broadband diode detector tells you what exactly, that there is energy being radiated within a broad swath of RF spectrum?

 

'Broadband diode' means VHF/UHF diodes like 1N34 germanium or 1N5711 schottky?

 

@Papabravo I think we both need to wait to hear more details of the application. The TS said he wants to "implement cell phone detector" but clearly, we don't know exactly what the TS wants. It has been a few days since his original posts, so maybe all he really wanted was to know the frequencies.

 

theres a neat dtetctor circuit here, http://www.techlib.com/
looki for " the fed detector", it detects digital signals in those bands. not for lstening, just detecting.

 

There's a neat detector circuit here, http://www.techlib.com/
look for the "FED detector", it detects digital signals in those bands.

I was about to post the link http://www.techlib.com/electronics/feddetector.htm here too. Techlib is one of the interesting hobby site.

not for lestening, just detecting.

The designer Charles Wenzel is saying there "Connecting an external speaker amplifier to the output of the first op-amp (pin 1) through a 4.7k resistor in series with a 1 uF capacitor will allow the signals to be heard."

 

they may be heard, but digital audio wont be decoded without the proper codec. you may hear a whine or buzz, but not voice.

 

Was there a particular reason you asked this question? The reason I ask is that building a detector for these frequencies is a non-trivial undertaking. Most cellphones use digital modulation and the signal levels are much lower and harder to detect than the old analog phones. Maybe you were going to use a preassembled module for this project?

No..I dont want to use any preassembled module for my project...simply i want to know the frequency with which my mobile is communicating and i want to build a circuit to detect that frequency

 

@Papabravo I think we both need to wait to hear more details of the application. The TS said he wants to "implement cell phone detector" but clearly, we don't know exactly what the TS wants. It has been a few days since his original posts, so maybe all he really wanted was to know the frequencies.

Yess i had the idea to block these frequencies also....if i build a circuit of same frequency will the signal will be blocked???i am new to electronics please he me in building this project

 

Actually, detecting the presence of a cell phone can be very simple - just a broadband diode detector can be enough. If you want to demodulate the signal...then yes, it can become a very involved project.

what is broad band diode detector??is it a diode....and is it possible to demodulate it?

 

Yes, broadband diode detectors use diodes.

Below is a very simple broadband detector.

Watch the video at the URL below.
http://rookieelectronics.com/sensor-rf-radiation-detector/

As stated in the user agreement that we all read carefully before joining the forum, discussion of jamming of cell phones is not permitted.

 

since nearly all cell phnes use digital modulation, a simple diode detector to demodulate willo not work, all you will hear is a buzz or whining sound. you can detect it though.

 

Yes, broadband diode detectors use diodes.

Below is a very simple broadband detector.

Watch the video at the URL below.
http://rookieelectronics.com/sensor-rf-radiation-detector/

As stated in the user agreement that we all read carefully before joining the forum, discussion of jamming of cell phones is not permitted.

Since it is broadband, and not selective, it will detect lots of things in addition to cellphones. So really knowing the frequencies used is of no particular value in this case.

 

I found the 1N4148 diodes used in many many places even for general purpose. Knowing the 4148 as broadband detector diode, feeling amazing. Once I used it in crystal radio, it was not working. I heated the diode with soldering iron 30 seconds and drop voltage became 160mV from 520mV across the diode, then I heared the radio.

Question is: I saw datasheet and didn't find the 'maximum frequency' rated, as transistors. How to assume the max freq?

 

As you go up in frequency it tends to be the inductance of the leads and not the diode itself which limits the operation.

 

Also the most critical specifications in ordinary small signal diode dataheets as far as max frequency is concerned are the reverse recovery time and the junction capacitance. Some diodes are made especially as detector diodes have much more comprehensive specifications including the kind of effects that Papabravo mentioned above.