On (21 Jan 97) Dave Franks wrote to Nasser Al-Thekair...
 DF> NA>Unfortunately a lot of people over here don't know about it!!
 DF> Most of the amateur radio operators do ...
 DF> NA>CB>SSB does away with one sideband and the carrier....this leaves
 DF> 1/3 the width
 DF> I believe this to be incorrect. The correct value would be 1/4 not
 DF> 1/3.
 DF> Half the power would be in the carrier, and the other half divided
 DF> equally between the sidebands, or 1/4 of the total power each.
It is not *power* that requires the bandwidth. It is the type of
emission.
CW requires less than 1 khz of bandwidth for transfering
*intelligence*.
SSB (depending on the frequency range of what is being passed) requires
about 2800 cycles or 2.8 khz for *full fidelity* on voice. That is
because the normal range of voice frequencies is about 400 to 2700
cycles. A *mans* voice ranges from about 400 to 1800 cycles. A *womans*
voice is pitched higher. About 1000 to 2700 cycles. Thus, the width of a
SSB signal varies from the *center* frequency (0 cycles) to the
*maximum* *conversational* voice frequency of 2800 cycles. All of the
intelligence is on one side of the *center* (or *carrier*) side of the
signal, depending on which *sideband* is chosen. This is called
"modulation product".  For lower sideband (LSB) it is below the center
freq. For upper sideband (USB) it is above the center freq.
Most SSB transmitters and microphones "shape" the audio somewhat to
*limit* the passing of frequencies from 400 to a maximum of about 2700
cycles. Some of the very latest ham transmitters use "digital
processing" to do the same. These units can emphasize or
deemphasize "pieces" of the audio spectrum to "customize" the entire
range of voice freqs transmitted.
As an interesting side note, our (United States) FCC (Federal
Communications Commission) will "cite" and possibly fine a US ham
operator for "out of band emissions" if his center (carrier) freq is
closer to the band edge than 2.8 khz, depending on which side band he
has chosen. US ham allocations allow the use of either side band on any
"phone band" portion within the "band allocation". *Conventional use* is
to use lower side band on 40, 80 or 160 meters, upper side band on all
the other *HF* frequencies (1.8 to 29.7 Mhz). Thus a 20 meter (14.000 to
14.350 Mhz is the US allocation for both phone and CW) SSB user on USB
can go no higher in frequency than 14.347.2 khz without becoming subject
to an "out of band" citation and possible fine by the FCC. This is
because his "modulation products" are assumed to be 2800 cycles wide and
are all above his center freq when he is on USB.
AM requires about 6 khz. But the same rule applies. A US ham on AM
may not get closer than 2.8 khz to a phone band allocation "edge".
CW may be operated within 1 khz of a band edge.
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