This is a Radio Frequency Field Strength Meter Circuit Schematic Diagram using only a single cell 1.5V battery.

rf field strength meter circuit schematic diagram

C1 need to be adjusted for peak reading. Then, to use it, turn on the transmitter and meter. For a perfect zero reading on the meter, turn off the transmitter and adjust R1. And then, once again turn on the transmitter with no audio modulation and go to your monitor points and take the readings. The monitor points should be far enough from your antenna but still have to have enough strong signal. You can do another experiment after taking a set of readings, and determine whether the signal strength was diminished or increased. Engineering logbook is useful for the reading record. Make not of the weather, is it dry or rainy, moist soil might give slightly better propagation.

Parts List:

  • Q1: 2N107 or GE-2, etc. (This is a pretty old circuit design. Any equivalent PNP transistor should work.)
  • R1: 50K potentiometer
  • R2: 1K, 1/2 watt
  • R3: 1K, 1/2 watt
  • J1: jack for antenna; the antenna must be insulated from the case
  • D1: 1N34
  • meter: milliammeter, 0 to 1 mA range
  • antenna: a 30 to 50 centimeter piece of stiff wire, or a generic telescoping antenna
  • L1 and C1 are chosen so that they form a resonant tank circuit at the frequency of interest.

Source : Medium Wave Alliance

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