Realistic TRC-449 Owner's Manual page 16

ADVANTAGES OF SSB OVER NORMAL AM
A theoretically perfect AM transmitter used in Citizens Band Radio Service as permitted by the
PMG will have the following maximum output power specification:
Carrier --- 4 watts with the capability of slightly less than 100% modulation
In order to fully Amplitude Modulate a 4 watt carrier, a full 2 watts of audio power is required. In this
case, only 1 watt of power can exist in each sideband. Since the carrier contains no intelligence, and the
sidebands duplicate each other, really only one sideband is required to transmit the required intelligence.
If we take the above transmitter and convert it to Double Sideband operation (eliminate the carrier
power), we can increase the power in the sidebands to 2 watts each, without overloading the circuitry.
Further, if we eliminate one of the two sidebands, we can put the full 4 watts of power into remaining
sideband. Thus, while an AM transmitter has only 1 watt of power in one sideband, an SSB transmitter
can have 4 watts of power in one sideband—or 4 times the power of an AM transmitter.
Thus, effectively an SSB transmitter with the same power limitations is 4 times more powerful than an
AM transmitter.
One further advantage, which is not often mentioned. Not only does the SSB signal take up only 1/2 of
the frequency spectrum space of an AM signal (only 1 sideband instead of 2), thus permitting twice the
number of stations to be in the same amount of band space—but also, at the receiving end, the receiver
only picks up 1/2 of the total AM bandwidth. This means that 50% less noise is amplified along with the
signal. This results in a 50% improvement in signal-to-noise figures; or, in more technical terms, a 3 dB
improvement.
Thus, given equal limitations and conditions, an SSB signal will be 4 times more powerful and will have
2 times the signal-to-noise advantage of an AM signal-8 times as effective. In technical terms, a 9 dB
advantage. Thus, for an AM transmitter to be equivalent in effectiveness it would have to be rated at 32
watts!
Enough said! We hope you're enthused.