RF related queries

[Anish]

Hi, long time...
I have some RF related queries.
I recently assembled a mobile phone detector circuit which detects the mobile phone when texting, calling/receiving. According to the description given by the author of circuit, its range is 1.5meters.
1. When I assembled the circuit on a solderless breadboard, I got range for about 10 to 20 meters. But when i soldered that circuit, I get barely one meter range why is this so? are the extra wires and bread board tracks increasing the range?

2. I did a pcb for the mobile bug and the range still decreased. I assembled as per the instructions given.

3. The circuit uses a opamp CA3130 but when I replace it with 741, it works even better in soldered pcb but doesnot work in breadboard?

These questions are puzzling me. I can't get answers anywhere. also, how can I increase the range of the circuit when i soldered it on the general purpose perf board? keeping a long antenna doesnot help.? do i need to do a precise antenna design?
I am not well with antenna design and RF.

Here is the circuit of the mobile detector :
http://www.electronicsforu.com/elec...le.asp?sno=429&article_type=1&id=412&tt=unhot

Thankyou,
Anish

 

[BobK]

Did you read this part:

Here the circuit uses a 0.22μF disk capacitor (C3) to capture the RF signals from the mobile phone. The lead length of the capacitor is fixed as 18 mm with a spacing of 8 mm between the leads to get the desired frequency. The disk capacitor along with the leads acts as a small gigahertz loop antenna to collect the RF signals from the mobile phone.

When you soldered it to the breadboard did you leave the leads to the capacitor at 18mm?

Bob

 

[Anish]

Did you read this part:



When you soldered it to the breadboard did you leave the leads to the capacitor at 18mm?

Bob

Hi Bob,

What do you mean by "soldered" it to the "breadboard"? I only assembled in the bread board
When i soldered it to the perf board, i kept exactly as told in the description since the cap acts as a loop antenna and is the key component of the module. (8x18mm)

 

[BobK]

Okay, that is what I was asking.

Bob

 

[Anish]

Yeah, i did as exactly said. But I can't figure out how breadboard assembling drastically increases the range of the circuit?
And also the op-amp part. I mean if it can run on 741, why use the costlier 3130?

 

[Anish]

Hi,
I searched over the internet, and found that I have one possibility to increase the range - i.e. to design an aerial. I am not familiar about aerials. But monopole aerial seems easy to make. If I make a monopole aerial for that circuit, will its range increase to say 5 meters?
Also, I have one question. The monopole aerial is made using coax cable. where do i connect the ground of the aerial? Is it to be connected to circuit ground itself?

Thanks.