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  1. #21
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    Re: RF Detector not detecting cellular phones

    Hi,

    I have to agree with Brian.

    I also find it hard where to begin.
    Like this comment or not: it is no HF design. I can see any design at all.

    A PCB layout is not simply joining some pins of electronic parts.
    "Joining" in the meaning of electrical connection, but even this is not true for all pins of your PCB. (Connector, diode)

    You think you now have a HF suitable GND plane. But it is not. In many cases your "GND plane" is not better than traces.
    You need to take care about current flow, current loops (mind that a singal is not from A to B you always need to consider the return path very carefully. If the return path is bad, your signal is bad and thus the performance of the whole circuit is bad.

    Sadly a forum can't replace school, reading books, experience...
    You can't expect to learn a HF design within a forum thread in a couple of hours where other need years of school.
    I design industrial electronics for decades now, always touching HF design, but after all the years I'm far away to be an HF expert.
    I just know some basics.

    But I don't want to discourage you. Go on. Maybe with another - not that high frequency - circuit.
    Maybe with this circuit ... but read some books about HF design first..

    Klaus
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  2. #22
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    Re: RF Detector not detecting cellular phones

    @M84AB3, being not so familiar with RF, I would consider before proceeding with the design of the PCB Layout, making computational simulations; there are tools suited for that. Note that the smallest λ/4 lenght for the frequency spectrum in question, Wifi in the case, may lie in the same magnitude of the board sizings, and it would not be improbable to have any kind of reflection canceling the signal injected by the antenna. The spectrum you are using is broad, ranging from 0.027GHz up to 2.4GHz, therefore what works well for one band is not necessarily supposed to work fine for another.
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  3. #23
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    Re: RF Detector not detecting cellular phones

    Quote Originally Posted by M84AB3 View Post
    This Antenna came off of a GPRS Shield v1.0 running a SIM900 module and works on the 850/950/1800/1900 bands. 850Mhz to 1900Mhz seems pretty "wide" to me.
    That spec is misleading. This is a simple narrow band antenna (monopole).

    On your PCB, trace length is an issue at 2.45GHz, and having GND doesn't solve that. For a quick test, take all components up to the diode off the PCB, and wire them as short as possible at the SMA. You can do some creative 3D wiring, it just needs to be SHORT.



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