I am a final year Electrical Engineering Student working on my senior project in Fairleigh dickinson university teaneck. I have a very urgent and important situation I need help with.
I am currently working on a cell phone detector also known as moblie bug. This device is supposed to sniff the presence of an activated phone a few centimeters away from it. There are two parts to the schematics of this device, the detector part and the indication part. I am having a lot of difficulty with the detector part, an IC1 (CA3130) along with a 0.22 capacitor forms the RF detector. IC1 is designed as a differential amplifier and the 0.22 uF capacitor is connected to its inputs. Using resistors and capacitor, the inputs are balanced. In the input balanced state, the OpAmp gives zero output. In this balanced state, a small voltage change in the input can change its output. In the stand by state, output of IC1 is zero. When the mobile phone radiation hits, 0.22 capacitor discharges its stored current to the inputs that momentarily upsets the balance and output of IC1 goes high. This high output pulse is used to trigger the monostable.
Question : I am having problems using the 0.22 micro farad as the main detector component, so I am looking for alternate devices or an alternate detector circuit configuration to detect RF signals from mobile phones, I was thinking the 50 dB GSM PA Controller AD8311 might be a good substitute for the detector part, if it is how can I make a circuit with it to help me detect signals from mobile phones?. I do not want to use the IC1 in combination with the .22 micro farad capacitor anylonger, it is too weak to detect signals acurately. Please help me with a detector type circuit and components, I would keep the indicator part the same as I have, I am employing the use of a buzzer, transitor and IC 555 as the indicator components.
Below is a schematic of the original circuit I am trying to use, if this helps to explain my intention clearly.
So please my question directly again is : how can I make a circuit to help me detect signals from mobile phones without the use of theIC1 in combination with the .22 micro farad capacitor as I have in my original circuit? , it is too weak to detect signals acurately. Please help me with a detector type circuit and components.
Thank you very much, I anticipate a very helpful response in my current situation.
I look forward to hearing from you.
I would not recommend AD8311 as it is a detector-controller. So its normal use case is to detect the signal at the output of a variable gain amplifier (or variable bias PA) and then adjust the gain of the variable gain element until its output power is at the desired level.
Instead I would recommend something like AD8314 or ADL5513. The more input range on the detector, the more sensitivity your circuit will have. You also need to think about selectivity. These devices are all broad band and will pick up what ever signal is on the antenna that is in the 1 GHz to 3 GHz range (input frequency range varies by device).
I'm not familiar with CA3130 and the associate 0.22 uF cap so I can't really comment on the questions you pose about them. If you are trying to capture and hold a transitional signal from a cell phone, take a look at ADL5500. This is an envelop detector with a low-droop peak-hold function.
Good luck with your project, It sounds interesting.