SSB Modulation with Phase Discrimination Method

Single Sideband modulation (SSB) is a technique used in radio communications to transmit information efficiently over limited bandwidth. SSB modulation can be done using different methods, and one of the most effective is the phase discrimination method and the other is SSB modulation using frequency discrimination method. In this article, we will explore SSB modulation with phase discrimination method, its benefits, and how it works.

What is SSB Modulation with Phase Discrimination Method?

SSB modulation with phase discrimination method is a technique where the suppressed carrier is multiplied with message signal in one channel and multiplied with -90 degree phase shifted message signal in the other channel and the product signal from the two channel are combined to produce the SSB signal. The phase discrimination method involves the use of a wide band phase shifter circuit to shift the phase of the input signal by 90 degrees. This allows for the separation of the upper and lower sidebands, which can then be amplified and transmitted.

How SSB Modulation with Phase Discrimination Method Works?

The following shows the phase discrimination based SSB modulation block diagram.

SSB modulation phase discrimination method circuit diagram

The SSB modulation with phase discrimination method involves the following steps:

The input signal \(m(t)\) is split into two path, the upper or in-phase channel and the lower or quadrature channel.
In the in-phase channel path, the input signal \(m(t)\) gets multiplied with the locally generated carrier signal \(m(t)\) in the DSB AM modulator or product modulator. The result is a DSB-SC signal in the in-phase channel.

\( s_I(t) = m(t)c(t) = A_m cos(w_m t) A_c cos(w_c t) = A_m A_c cos(w_m t) cos(w_c t) \)

In the quadrature channel path, the input signal \(m(t)\) goes through a Hilbert transformer or phase shifter that shifts the phase of the input signal by 90 degrees. That is the output from phase shifter is \( \hat{m(t)} \). This phase shifted signal is multiplied with the carrier 90 degree phase shifted carrier signal \(c(t)\) by the product modulator or DSB balanced modulator to get another DSB-SC signal.

\( s_Q(t) = \hat{m(t)} c(t-) = A_m sin(w_m t) A_c sin(w_c t) = A_m A_c sin(w_m t) sin(w_c t) \)

Depending upon whether upper sideband SSB signal is required or lower sideband SSB modulated signal is required at the output, the DSB signal from the in-phase channel and the quadrature channels are either added or subtracted.

\(s_{ssb}(t) = \frac{A_c}{2}cos(w_ct) m(t)\mp \frac{A_c}{2} \hat{m(t)} sin(w_ct) \)

where, \(s_u(t) = \frac{A_c}{2}cos(w_ct) m(t) - \frac{A_c}{2} \hat{m(t)} sin(w_ct) \)

and, \(s_l(t) = \frac{A_c}{2}cos(w_ct) m(t) + \frac{A_c}{2} \hat{m(t)} sin(w_ct) \)

which is also the equation of SSB modulation. The above SSB modulation circuit diagram is based on this SSB modulation formula.

The SSB signal is then amplified and transmitted.

Benefits of SSB Modulation with Phase Discrimination Method

Efficient use of bandwidth: SSB modulation with phase discrimination method uses only half the bandwidth of conventional AM modulation, making it an efficient method of transmission.
Better signal quality: By removing one of the sidebands, the SSB signal with phase discrimination method is less susceptible to noise and interference, resulting in a better signal quality.
Increased range: SSB modulation with phase discrimination method can transmit over longer distances compared to conventional AM modulation.
Cost-effective: SSB modulation with phase discrimination method is a cost-effective method of transmission since it requires less bandwidth and has better signal quality, reducing the need for expensive equipment.

Video demonstration

Watch the following video which demonstrates how the phase discrimination SSB modulator circuit works.

Conclusion

SSB modulation with phase discrimination method is an effective technique for transmitting information over limited bandwidth. Its benefits include efficient use of bandwidth, better signal quality, increased range, and cost-effectiveness. By understanding how SSB modulation with phase discrimination method works, engineers and technicians can design and implement more efficient radio communication systems. It is one of the two methods of SSB modulation techniques, the other one being the Frequency Discrimination SSB Modulation. The SSB signal can be demodulated using SSB Demodulation with Coherent Detection method.

References:

[1] AM modulation and demodulation Circuit

[2] Different Types of AM Modulator and Demodulator Circuits

[3] SSB signal generation in Matlab