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    learning to detect radio signal.

    if i use an antenna to pick up a radio signal, then amplify the signal from the microvolt range to 100 millivolts, could i detect the radio signal with a multimeter? i don't want to demodulate the signal. i just want to make sure the signal is there.

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    Re: learning to detect radio signal.

    For the detection of the carrier without the use of a resonant circuit (preferably variable) after the antenna, you would only pick up white noise, whose higher frequencies would certainly be eliminated by the multimeter BW limit, supposedly an ordinary DVM model is what you are talking about, which were not assigned to such a task. You definitely need to get introduced into the telecommunications subject a little more deeply before ask this kind of question here.
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    Re: learning to detect radio signal.

    so the ordinary multimeter cannot detect higher frequencies?



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    Re: learning to detect radio signal.

    If you want that an RF signal can be measured by means of a simple DMM you need a detector. It converts the RF level to a DC voltage that can be easily measured. Unless you filter the signal coming from the antenna in the band you wants, your detector will see all the signals picked-up by the antenna. This means the output of the detector will be the DC equivalent to the sum in power of all the signal that are in the band of the detector. The filter you have to implement depends from the specs of your signal and those you have to reject.
    If you are sure the signal you want to detect is much greather than all the other signal that could reach the antenna, then you could eliminate the filter.
    In any case have a look to
    https://www.analog.com/en/products/r...detectors.html
    https://www.maximintegrated.com/en/p...detectors.html
    https://www.minicircuits.com/WebStore/pd_coax.html



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    Re: learning to detect radio signal.

    Yes, an ordinary meter will measure voltage up to its maximum frequency. Typically for DVMs that will be a few KHz.

    You can rectify the signal and measure the resulting DC, this is how "field strength" meters work and the frequency limit is then decided by the physical properties of the signal path and the rectifier. F.S meters work up to hundreds of MHz.

    The problem with simply amplifying and measuring is, as Andre pointed out, it 'sees' a mixture of all the signals within its bandwidth at once. The signals will be of many different frequencies and more importantly, many different phases. The signals don't add up in amplitude, as many as add up will subtract or partially subtract and you could even get an average of zero overall. It will work if only one signal is present (unlikely!) or if one signal is significantly stronger than all the others.

    If you want to detect a radio signal and measure the voltage it produces, you need some kind of selective filter that only allows the one signal to get through and excludes all others. This is basically how a radio receiver works, you select the station you want with a tunable filter, amplify the selected frequency then 'detect' the amplitude or frequency shift to recover the audio.

    Brian.
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    Re: learning to detect radio signal.

    i might start with lower frequencies, but what if i use a filter to filter all other radio signals, 5.8 gigahertz is the only frequency that gets through, and i amplify the signal, could an ordinary multimeter detect that?



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    Re: learning to detect radio signal.

    You stand absolutely zero chance of a multimeter reading that!

    Consider that when using frequencies in that range you need at the very least coaxial cables and more likely matched strip lines simple to carry the signal at all. Expecting it to travel along flexible meter probe wires is definitely a no-go!

    When I said 'a few KHz' in post #5, that is exactly what I meant, maybe up to say 3KHz if you are lucky. You are asking for it to work at 2 million times higher frequency!

    To measure at 5.8GHz, first consider how you are going to carry the signal, think of coupled line filters then amplifiers and finally rectifiers and possibly further amplifiers. Most equipment for measuring at those frequencies does so by down-mixing to a more manageable frequency first.

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    Re: learning to detect radio signal.

    i think i found a 6 gigahertz spectrum analyzer on the internet at a price i can afford. i should use that instead?



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    Re: learning to detect radio signal.

    A spectrum analyzer would be a far better instrument for measuring at those frequencies!

    Brian.
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    Re: learning to detect radio signal.

    is it possible to build a spectrum analyser at home?



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    Re: learning to detect radio signal.

    A software defined radio USB stick like nooelec NESDR covers the 25MHz - 1750MHz frequency range for about $25.



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    Re: learning to detect radio signal.

    that does not answer my question, can you build a spectrum analyser at home?



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    Re: learning to detect radio signal.

    Hi,

    that does not answer my question,
    Yes, there are people that can build their own spectrum analyzer.

    But I doubt it makes sense for a single piece. It needs a lot of HF experience, high speed ADC experience, PCB layout experience and the knowledge abot the math.

    Klaus

    I forgot to mention that one needs good programming skills, maybe FPGA design skills, too.
    Please don´t contact me via PM, because there is no time to respond to them. No friend requests. Thank you.



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    Re: learning to detect radio signal.

    Hi,

    How's that inverting amplifier circuit coming along?

    Quote Originally Posted by dl09 View Post
    that does not answer my question, can you build a spectrum analyser at home?
    No, you absolutely cannot. Besides serious questions one must ask oneself and answer honestly about required patience to study required fields properly and diligently, lack of knowledge (What is Johnson noise? What is a bandpass? What changes by - 2mV/°C? What is PCB layout?...Just for starters... ), lack of experience and ability to make one - one must start with honest, realistic self-appraisal..., there are major issues regarding inadequate equipment to build one, Inadequate equipment to test one, inadequate conditions to test one, presumably common sense about the financial resources needed for the components and test equipment, the time needed...

    Just buy one. And read the instruction manual and genuinely absorb the words therein, read - not just rush through and not pay attention to anything whatsoever.

    I have answered your question explicitly. Now there is no longer any need to ask it over and over and say nobody answered the question.


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