Realistic TRC-449 Owner's Manual page 15

27.016 MHz
CARRIER
(SUPPRESSED)
LOWER SIDEBAND
(SUPPRESSED)
UPPER SIDEBAND
I / (SUPPRESSED)
I
I I
CARRIER
/
(SUPPRESSED)
SSB (SINGLE SIDEBAND) . . . . WHAT IS IT?
We thought you'd be interested in knowing and understanding something about the SSB function and
capability of your Transceiver.
To understand SSB, we need to know what an AM (Amplitude Modulated) signal is.
Amplitude Modulation is a form of heterodyning—mixing 2 signals together electrically. In the process of
mixing, 3 signals result. Example.
An R.F. signal at 27.015 MHz (channel 1 C.B.) is mixed with (modulated by) a 1000 Hz tone.
The resulting signals —
27.015 MHz = original or "carrier" signal
27.015 MHz — 1000 Hz (27,015,000 minus 1000) = 27.014 MHz, the Lower Sideband
27.015 MHz + 1000 Hz (27,015,000 plus 1000) = 27.016 MHz, the Upper Sideband
CARRIER
27.015 MHz
0
LOWER SIDEBAND
27.014 MHz
UPPER SIDEBAND
27.016 MHz
FREQUENCY
Notice that the communication or intelligence (the 1000Hz tone) is contained in each sideband. The
Carrier contains no intelligence. This fact is vital!
For the sake of communication, all we need to receive is the 1000 Hz tone. The receiver only needs to
recover one signal, and yet we are transmitting 3 signals. Not only are we sending 3 signals, but also we
are wasting most of our power in one of them (which carries none of the intelligence, i.e. the carrier,
27.015 MHz) and the other two signals duplicate each other!
Thus, if we can eliminate the carrier (not needed for communication)and can send only one of the side-
bands (since they duplicate each other's information anyway), we could concentrate all of the trans-
mitting power into one sideband. This is exactly what Single Sideband accomplishes.
Single Sideband transmissions incorporate only one of the sidebands—i.e. in the example above, only the
upper sideband at 27.016 MHz or only the lower sideband at 27.014 MHz. The second sideband and the
carrier are eliminated in the early stages of the transmitter circuitry.
SSB LOWER SIDEBAND
SSB UPPER SIDEBAND
FREQUENCY FREQUENCY
When only one sideband is transmitted, we can concentrate all of the available power in this one side-
band, greatly increasing the effective power of an SSB signal as compared to an AM signal.
See Advantages of SSB Over Normal AM.