Testing the Transmitter and Receiver

1. Obtain a 1 k potentiometer and install it in your transmitter circuit.
2. Your coils should be wound such that the turns are near the notched end of the PVC. Each coil was wound either clockwise or counter-clockwise as seen from the notched end. Observe and record the relative orientation of the windings. That is, record whether the transmitter coil is wound clockwise or counter-clockwise as seen from the notched end. Repeat for the receiver coil. Orient your transmit and receive coils such that the magnetic flux produced in the transmitting coil will be maximally coupled to the the receiver coil. To do this, place the notched ends of the coils as close to each other as possible with a common axis. You will find that it is necessary to keep the coils stationary during the measurements or the measurements will change with time causing frustration! You may find it helpful to insert a pen or pencil through the two coils to stabilize them while you make your measurements.
3. Set the function generator to produce a sinusoidal voltage at a frequency of 10 kHz and a peak-to-peak value of 5V. Using both channels of the scope, measure the peak-to-peak voltage across both the transmit and receive coils. Adjust the potentiometer until the voltage across the transmit coil is maximum. Increase the frequency by a factor of ten and make another set of measurements. Continue until you have reached the frequency limit of the function generator. Comment on any unusual waveshapes observed.
4. The parallel RC circuit ( and ) in the receiver has a time constant as explained in the introduction of this lab exercise. This time constant determines both the rate that will charge as well as the rate it will discharge. Considering the values of and you have on your board, what is the value of this time constant? Measure the voltage across and at a frequency of 200 kHz (using the scope) along with the voltage across the transmitter coil. You choose the amplitude. Slowly vary the amplitude of the transmitted signal by varying the potentiometer. Observe the transmitted signal strength and the DC value across and as you adjust the potentiometer over its entire range. Explain what you observe.