VHF field strength meter

john April 15, 2009 9 Comments

Description.
This is a simple and low cost wide band VHF field strength meter. The field strength is measured by converting the radio signal to DC and measuring it. The RF signal will be picked up by the coil and rectified by the diode D1.Even a very small DC voltage is sufficient to alter the biasing of FET and it will be reflected in the meter as an indication of the presence of a radio signal. The meter can be calibrated by adjusting the preset R2 to make meter M1 read ZERO in the absence of any radio signal. This circuit is not very sensitive, but can sense radio signals from hand held FM transmitters up to a distance of few meters( ideal for theoretical demonstrations).

Circuit diagram with Parts list.

vhf-field-strength-meter

Notes.

  • The circuit can be assembled on a general purpose PCB.
  • Use a 9V PP3 battery for powering the circuit.
  • Use a 250uA FSD current meter for M1.Using a lower FSD meter will improve sensitivity.
  • The coil L1 can be made by making 6 turns of 20 SWG enameled copper wire on a ¼ inch plastic former.
  • The antenna can be a telescopic whip antenna.
Comments
  • HARRY
    March 13, 2014

    plz, l need ur help in building electromagnetic radiation meter that can measure frequency range from 50Hz to 30GHz and also the output will be digit of 16by4 LCD display.

    can inductor coil increases the strength of electromagnetic radiation meter? if Yes
    the types of the inductor
    can l able to lay my hand on a sensor the can measure that electromagnetic radiation

  • maaz ranjha
    January 23, 2012

    i want to catch the signal of cable network with tv antinna

  • seetharaman
    August 21, 2011

    Hi Olawuyi this is wide band VHF field strength meter responding to entire VHF band of frequencies.

  • olawuyi
    August 20, 2011

    I need a field strength meter for FM, this circuit you have for fm, how do I select the frequency, I mean the tuning

  • Seetharaman
    November 26, 2010

    Hi Akeredolu this circuit can respond to both FM and AM field strength. which frequency range you want to cover. L1 alone requires replacement for different range of frequencies.

  • Akeredolu Bunmi Jacobs
    November 25, 2010

    Pls, could u help me to design AM field strenght meter? thanks

  • Anu George
    October 12, 2009

    we are planning to do a project that measure the intensity of electromagneticfield and display it on digital form. please help us

  • August 31, 2009

    We are working in a project for the same I require your kind assistance.

    • jojo
      August 31, 2009

      what help u need vasanth?

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