+ Post New Thread
Results 1 to 7 of 7
  1. #1
    Full Member level 6
    Points: 2,527, Level: 11

    Join Date
    May 2013
    Posts
    398
    Helped
    79 / 79
    Points
    2,527
    Level
    11

    Antenna output voltage vs. received RF power

    Hi everyone,

    I'm new to RF design and aware that this may be a trivial and/or silly question for the RF experts on here.

    I'm wondering which parameters, for planar antennas (such as patch antennas), are affecting the output voltage of the antenna (Vpp). Is that the frequency of the signal(s), the power of the received signal(s), a combination thereof, or something completely different? Second part of the question: for a certain antenna design, is it possible to deduce the received power strength and/or frequency from the output voltage, possibly with calibration?

    If I wanted to measure the received power level in a very narrow band of frequencies, what would be the best approach to do this?

    If anyone could direct me to relevant literature on this topic, I would be very grateful.

    •   Alt11th January 2017, 02:36

      advertising

        
       

  2. #2
    Advanced Member level 5
    Points: 10,861, Level: 25

    Join Date
    Apr 2010
    Posts
    1,656
    Helped
    359 / 359
    Points
    10,861
    Level
    25

    Re: Antenna output voltage vs. received RF power

    the output voltage of the antenna is dependent on the combination of the power of the received signal, the bandwidth of the antenna and the impedance of the load connected to it.

    To measure the received power level in a very narrow band of frequencies , best approach is to have the test instrument for that purpose.



    •   Alt11th January 2017, 04:45

      advertising

        
       

  3. #3
    Full Member level 6
    Points: 2,527, Level: 11

    Join Date
    May 2013
    Posts
    398
    Helped
    79 / 79
    Points
    2,527
    Level
    11

    Re: Antenna output voltage vs. received RF power

    Quote Originally Posted by srizbf View Post
    the output voltage of the antenna is dependent on the combination of the power of the received signal, the bandwidth of the antenna and the impedance of the load connected to it.
    Assuming that the load impedance is constant, it can be deducted that the power of the received signal can then be correlated to the output voltage, if the bandwidth of the antenna is reasonably flat. However, I do not have much experience with antennas yet. Which type(s) would be good choices in a range from 433 MHz to 2.45 GHz?

    Quote Originally Posted by srizbf View Post
    To measure the received power level in a very narrow band of frequencies , best approach is to have the test instrument for that purpose.
    Unfortunately I don't have any high end test instruments available, and they're way out of my budget range. I do, however, have a CCC 2015 Rad1o Badge (SDR dev board) at my disposal. Can I work around it using that board?



    •   Alt11th January 2017, 12:20

      advertising

        
       

  4. #4
    FvM
    FvM is offline
    Super Moderator
    Points: 221,762, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    38,051
    Helped
    11651 / 11651
    Points
    221,762
    Level
    100

    Re: Antenna output voltage vs. received RF power

    It would be probably helpful if you tell what your actual design/measurement problem is.

    Is the primary quantity of interest field strength or received power with a specific antenna? What's the field strength range, how accurate want you measure it?

    Quantitative level measurements "in a range from 433 MHz to 2.45 GHz" will typically use a wide band antenna like log-per which have a fairly constant gain over a wider frequency band.

    Alternatively you can use dipoles with variable length that are tuned to the respective frequency.

    For high level measurements, e.g. calibration of susceptibility test systems, active wide band antennas are used as field strength monitors.

    I doubt that you'll have much success without acquiring some basic RF knowledge.



  5. #5
    Full Member level 6
    Points: 2,527, Level: 11

    Join Date
    May 2013
    Posts
    398
    Helped
    79 / 79
    Points
    2,527
    Level
    11

    Re: Antenna output voltage vs. received RF power

    Quote Originally Posted by FvM View Post
    It would be probably helpful if you tell what your actual design/measurement problem is.
    Ideally, I'd like to be able to measure the field strength in the frequency range between ca. 430 MHz and 2.5 GHz, in bands of 1 to 2 MHz wide, with a fixed antenna.

    Quote Originally Posted by FvM View Post
    Quantitative level measurements "in a range from 433 MHz to 2.45 GHz" will typically use a wide band antenna like log-per which have a fairly constant gain over a wider frequency band.
    Most of these log periodic antennas seem to be quite large and cumbersome. Is it a viable alternative to use multiple smaller antennas (with narrower bandwidth) and switch between them with an RF switch? Ideally I'd like to use wire antennas or PCB antennas.

    Quote Originally Posted by FvM View Post
    I doubt that you'll have much success without acquiring some basic RF knowledge.
    Indeed, so I'm doing my best to catch up with the basics in the context of this project, but unfortunately it's -- as usual -- a tight deadline.



    •   Alt11th January 2017, 23:49

      advertising

        
       

  6. #6
    Super Moderator
    Points: 43,858, Level: 51

    Join Date
    Apr 2011
    Location
    Minneapolis, Minnesota, USA
    Posts
    10,824
    Helped
    2157 / 2157
    Points
    43,858
    Level
    51

    Re: Antenna output voltage vs. received RF power

    The grid dip meter is mentioned often as an important rf measuring instrument. Its response is based on LC resonance. The jfet version causes the meter to dip when it detects rf energy. (There are versions which use a bjt, in case a jfet can't be obtained.)

    Its operating principle may be suitable to adapt to what you wish to do.

    One article describes how you can easily measure different rf bands. Wind different size coils, and attach them cardboard forms which are cut to fit over the detection element in your meter. It does not require making and breaking electrical contact. No soldering is needed.

    Example articles:

    https://g4rvh.files.wordpress.com/20...-dip-meter.pdf

    http://qsl.net/yo4rlp/wshp/gdo.html



  7. #7
    FvM
    FvM is offline
    Super Moderator
    Points: 221,762, Level: 100
    Awards:
    1st Helpful Member

    Join Date
    Jan 2008
    Location
    Bochum, Germany
    Posts
    38,051
    Helped
    11651 / 11651
    Points
    221,762
    Level
    100

    Re: Antenna output voltage vs. received RF power

    You didn't yet answer to the level accuracy point.

    Consider that the accuracy of field strength measurements made with "high end" equipment (calibrated antennas and state-of-the-art spectrum analyzers or test receivers) isn't assumed better than +/- 1 dB in EMC standards, you should account a larger error margin with non-standard equipment.

    SDRs like the CCC radio badge are basically suited for semi-quantitative measurements, but you'll probably need an RF generator or a power meter and an attenuator set for level calibration.

    I prefer a 400 MHz to 6 GHz logper antenna in combination with a regular spectrum analyzer for pre-compliance tests of sub-GHZ small radio devices. Using multiple antennas with a mux doesn't sound reasonable, too much mutual coupling and level error by the mux. I would rather use one or two tuned dipoles or individual fixed dipoles and change the frequency manually.



+ Post New Thread
Please login
--[[ ]]--