Raspberry Pi for Home build frequency spectrum analyzer

Discussion in 'The Projects Forum' started by hugeRune, Nov 12, 2014.

  1. hugeRune

    Thread Starter New Member

    Nov 5, 2014
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    Raspberry Pi for Home build frequency spectrum analyzer
    I would like to use my Raspberry Pi to build a frequency spectrum analyzer (for the 5Ghz band) but looking at the high costs for commercial models I feel that I am missing something. So instead of just going ahead, and probably wasting a lot of time and some money, I would like to ask for some expert advice or warning. Here are my thoughts so far:
    Possible solution 1: Use a 5 GHz Wifi USB adaptor to receive Radio signals (The adaptor should be able to receive a bandwidth of 40Mhz somewhere around the 5 MHz wifi frequency). I am not sure how to “tell” the wifi adaptor to provide the raw signal in digital form so that I could use the Raspberry to do a Fast Fourier Transformation on it.
    Possible solution 2: Build an antenna suited to the 5GHz frequency (My understanding is that this antenna will pick up a whole bunch of frequencies with different amplitudes). Not sure if a filter would be required to clean the signal. In the next step I would connect the antenna to an Analog/Digital converter and in this way send the digital signal to the Raspberry Pi. There I would do a Fast Fourier Transformation to identify the relevant sinuous frequencies that make up the overall received signal.
    Any thoughts would be really welcome. As I stated before I feel that I am missing something, probably due to my lack of profound (especially practical) knowledge of radio technology.

    Jens
     
  2. Papabravo

    Expert

    Feb 24, 2006
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    Working with microstripline circuitry in the 5 GHz range will be expensive no matter what you do. You could spend a small fortune on test equipment just to develop and debug what you need. If you need a spectrum analyzer, then rent one. I doubt you can cobble one together for cheap, even if the Pi can do the digital processing.
     
    Last edited: Nov 14, 2014
  3. MrChips

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  4. hugeRune

    Thread Starter New Member

    Nov 5, 2014
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    Dear Pappabravo,

    I am not sure if I understand your comment correctly (Most Probably due to my lack of knowledge in the matter) but I assume you are referring to my idea to build an antenna suited to the 5GHz frequency. Couldn´t I just buy an Wifi 5GHz adapter and use the antenna and some of the power circuits?

    This question probably shows that I am really a newby in this field.

    Best regards,

    Jens
     
  5. Papabravo

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    Feb 24, 2006
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    I don't know if purchased modules will do the job. A 5 GHz antenna could conceivably be built on a PC board along with some of the front end RF circuitry. You cannot use the RF directly for your purposes; you will have to convert the signal to a lower frequency so you can sample it and extract the information you need for a spectrum display. This is not an area that I would recommend for a first time project. You could however acquire the required knowledge over a period of time and get there eventually. I had an uncle who spent 60 years building a race car with...unusual handling capabilities. He was one patient fellow and understood the process of stepwise refinement.
     
    Last edited: Nov 14, 2014
  6. alfacliff

    Well-Known Member

    Dec 13, 2013
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    a 5ghz adapter? you mean kind of like wifi? that would not work because the output would be from the demodulator. modules from minicircuits lab and others would work, and have been used to build spectrum analyzers before. a suguestion would be to research SDR software defined radio, a reciever simalar to that but for 5 ghz would work.
     
  7. hugeRune

    Thread Starter New Member

    Nov 5, 2014
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    I guess 60 years is more time than I want to spent :) So the building an antenna approach is out. Thanks Papabravo for the advice
     
  8. hugeRune

    Thread Starter New Member

    Nov 5, 2014
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    Hello Alfacliff,

    thank you for your hints. I will spent some time on following up on your suggestions. My other idea is to find a USB Adapter and try to use it in monitor mode (with Linux OS) and see what information I can read with the Raspberry.

    Thanks a lot!
     
  9. Papabravo

    Expert

    Feb 24, 2006
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    If you're going to use minicircuits components you'll have to learn RF design techniques PDQ. You'll also need some test equipment. I wasn't suggesting that it would take you 60 years. For most of those 60 years there was no such thing as a personal computer. That and he kept learning new things along the way that nobody else knew; it was after all a research vehicle.
     
  10. alfacliff

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    Dec 13, 2013
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    minicircuits has modules also, not just components. just connect together and go. have to learn how to put connectors on small cable tho.
     
  11. Papabravo

    Expert

    Feb 24, 2006
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    I did say in my first post that I didn't know if there was a module that would fill the job. There might well be but you may have difficulty finding and applying it. You'll still need test equipment and enough understanding of RF design and specifications to put it together and make it work.
     
  12. hugeRune

    Thread Starter New Member

    Nov 5, 2014
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    Hello Alfacliff,

    I know I should learn this myself and not just aks but anyway which module would I look for at www.minicircuits.com
     
  13. hugeRune

    Thread Starter New Member

    Nov 5, 2014
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    After reading a lot more about Digital Signal Processing (DSP) I have now a better understanding why my original envisioned solution will not work. Buying an embedded wifi module (http://www.microchip.com/pagehandler/en-us/technology/wifi/home.html) to get the physical layer information seems like a great idea. Unfortunately all embeded wifi modules that I could find have the MAC layeralready included and I think this means that I will not be able to get level 1 information :-(
     
  14. Papabravo

    Expert

    Feb 24, 2006
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    On the theory that you can often get to your goal faster by taking intermediate steps. You could get a general coverage receiver like a K3 or a Flex 3000 which has the interfaces you need for building the Pi part of your project.
     
  15. hugeRune

    Thread Starter New Member

    Nov 5, 2014
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    Thanks Papabravo!

    I am currently pursuing the embedded wifi module but if in case that does not workout I might try a general coverage receiver
     
  16. Papabravo

    Expert

    Feb 24, 2006
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    If that does work for you then adding a down converter from 2.4 GHz to 28 MHz (10 Meter) band and you are done.
     
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