In a balanced modulator circuit, 3 transistors are used. Q1s emitter is connected to Q2s emitter and Q3s collector. Q3 acts as a current source for Q1 and Q2. If the RF input is applied to the bases of Q1 and Q2 in phase, current through both transistors will be identical and the voltage difference across the output will be zero. This has balanced out the carrier. Then, the audio input is appied to the base of Q3. This upsets the circuit balance which results to the mixing of the audio and RF signals across Q1 and Q2. Sidebands appear at the output while the carrier or RF input does not since it is a common-mode signal.

Firstly, we constructed a 100KHz source and connected it to a balanced modulator that was constructed using a 1490 IC. The output waveform generated in the oscilloscope was a DSBSC AM wave. When R1 ws varied both clockwise and counterclockwise, the amplitude of the signal was adjusted. When rotated clockwise, the signals amplitude increases. On the other hand, when rotated counterclockwise, the signals amplitude decreases. Then, sine input was disconnected to R1. R2 was adjusted for minimum output. When sine input was reconnected to the R1 and R1 was adjusted for maximum output, we measured 232mV in the peak sideband output voltage. From this, we can compute for the carrier suppression (in dB) from so we get 17.207dB.

In an AM system, most of the transmitted power is in the carrier. This transmitted power is wasted because it does not contribute to the intelligence being conveyed. This wasted carrier power can be eliminated by suppression or removing the carrier before transmission using a balanced modulator. The balanced modulator mixes the audio and RF carrier. It allows only the mixing products or sidebands to pass to the output. The resultant signal can be transmitted and receive without a carrier which means it can offer more efficient transmission than standard AM because there is less power wasted.

In a diode detector circuit, the input is an AM waveform that has been selected and amplified by the previous stages in the receiver. It is applied to D1 which acts as a half-wave rectifier. The positive half cycle causes D1 to conduct which develops positive pulses across R1. D1 cuts off the negative half cycles of the RF input. When S1 s closed, C1 is placed in parallel with R1. C1 quickly charges through D1 to the peak of each positive pulse. Between pulses, C1 attempts to discharge through R1. As a result, the voltage across C1 follows the envelope of the AM waveform. Thus, the output looks like the upper envelope with a small ripple. First, we constructed an AM generator circuit. We set the modulation to approximately 50%. Then, we connected the diode detector circuit to the AM generator circuit. The oscilloscope shown a demodulation signal. The R1 was set to vary the percent modulation. The detected signal changes the output amplitude of the signal. This can be used to fix the output signal. Then, R1 was turned clockwise until the AM waveform is overmodulated. The detected output became distorted. Diode detector is commonly used in virtually AM receivers. With a diode detector connected, signals will be restricted from passing in the reverse direction, and will pass only in the forward direction. Its purpose is to recover the envelope from the AM waveform.