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RF related queries

Discussion in 'Radio and Wireless' started by Anish, Mar 13, 2014.

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  1. Anish

    Anish

    46
    0
    Feb 5, 2011
    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
     
  2. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    Did you read this part:

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

    Bob
     
    Last edited: Mar 13, 2014
  3. Anish

    Anish

    46
    0
    Feb 5, 2011
    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)
     
  4. BobK

    BobK

    7,682
    1,686
    Jan 5, 2010
    Okay, that is what I was asking.

    Bob
     
  5. Anish

    Anish

    46
    0
    Feb 5, 2011
    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?
     
  6. Anish

    Anish

    46
    0
    Feb 5, 2011
    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.
     
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