Grid dip meters represent a simple example of radio frequency, or RF, test equipment that dates back to the days of vacuum tubes. Grid dip meters are simple to make as they are essentially an oscillator with the coil exposed outside the instrument's case. Most dip meters have the coil mounted in a socket where additional coils can be inserted to expand the meter's frequency range. Amateur radio operators most often use the grid dip meter to check the resonant frequency of their antennas.
Select the oscillator coil that covers the frequency of the antenna you will measure. The coil's frequency range is printed on the coil's label.
Insert the two coil leads into the dip meter's external coil jacks.
Move the dip meter's selector switch to the "OSC" or oscillator setting.
Set the meter's power switch to the "ON" position.
Turn the sensitivity knob on the dip meter fully counter-clockwise.
Form a one-inch diameter loop in an alligator test clip lead. Form the loop by grabbing the test lead ends with each hand and forming a circle in the middle of the test lead. Place a wire tie through the loop and tighten to prevent the loop from changing size.
Attach one of the alligator clips to the antenna near the centre insulator. Attach the other alligator clip to the antenna on the opposite side of the centre insulator.
Hold the dip meter's coil about 1/2 inch from the test lead loop.
Set the meter to the lowest frequency by turning the frequency knob fully counter-clockwise. Slowly turn the dip meter's frequency knob clockwise until the meter's needle swings to the left or dips.
Move the dip meter slowly away from the test lead loop. Turn the frequency knob from the right to the left of the point where the needle dips. Stop moving the dip meter away when the needle's dip is sharp and occurs with only a slight adjustment of the frequency knob.
Read the frequency off the dip meter's display. This is the antenna's resonant frequency.
Things you need
- Grid dip meter
- Alligator clip test lead
- Wire tie