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Generating High Frequency Signals

  1. Aug 9, 2012 #1
    What is the best way to generate a signal with a high frequency (700 MHz - 30 GHz)?

    Is there a preferred circuit diagram for such a design, or is it better to use a processor of some kind?
    Is it really heavily based on the length of the antenna (dipole)?

    I am trying to do it as cheap as possible but I am not sure if that is very possible.

    Thanks in advanced for any ideas.
  2. jcsd
  3. Aug 9, 2012 #2
    Generating the signal is not really the problem.

    Handling it ie successfully connecting to generator and using it is the really difficult part.

    You need a good working knowledge of transmission line theory to do this and I worry from the above question.

    How would you know if you have achieved your objective?
  4. Aug 9, 2012 #3


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    Staff: Mentor

    What frequency band do you want to transmit in? Do you have a license to transmit in that band?
  5. Aug 9, 2012 #4
    Well actually the main design is an electromagnetic shield. We have an circuit inside a faraday cage and want to make sure it reflects/blocks higher frequencies (700MHz - 30 GHz). We have the impedance of the box as low as we can but we need to verify with actual testing.

    It is a small scale low power test (or will be) so I am hoping a license would not be needed.

    The signal can be just random noise just need it to be about 1000 MHz.

    Is what I am asking possible or "easier" to build?

    Thanks again
  6. Aug 9, 2012 #5


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    Staff: Mentor

    There is an industry standard test for Radiated RF Immunity -- EN 61000-4-3


    The test is conducted inside an anechoic chamber to keep the test signals from violating FCC rules. If you have your own shielded room, you could potentially do a similar test, but renting the test equipment would be more expensive than going to your local EMC test lab and renting some "engineering test" time.

    Google for "EMC Test Lab" in your area, and give them a call to get a quote. That would be my recommendation. I've spent a *LOT* of time in such labs, testing and improving products that I have been on the design teams for.
  7. Aug 10, 2012 #6
    Okay great thank you, I will look into one around us, that sounds like a convenient way to do the higher frequency testing.

    What if I want to test for frequencies around 100 MHz? I can do that without violating FCC rules as long as I keep the power output below 1 watt correct?

    What is the best circuit to use for that kind of a signal output? Again it can be just random noise.
  8. Aug 10, 2012 #7


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    Staff: Mentor

    The allowed unlicensed power levels vary with the band, but 1W is much too high for most bands. Up in the microwave oven band (WiFi around 2.4GHz), the power limits are relaxed, but for most other bands that I'm aware of the power limits are quite low unless you are licensed for that band.

    You would need some sort of well-shielded room or chamber in order to do any immunity testing on your own.


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