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| In article <f6ljtr$euq$1@nnrp.linuxfan.it>,
John Smith I < assemblywizard@gmail
.com> wrote:
> Ron Baker, Pluralitas! wrote:
>
>
> This is your last question of 1001 questions:
>
> Since the information (modulation/voice) is repeated in both sides of
> the modulation envelope in am, ssb "chops off" one half of the envelope.
> The receiver is responsible for "mirroring" the other and reproducing
> the information on that end--this allows for almost doubling the
> effective range of am.
The range is increased, but not for the reason you stated (and BTW, he
asked about DSB; you responded about SSB).
There are two primary reasons why suppressed carrier SSB has more
"range":
1) The receiver can have half the bandwidth as compared to AM; that
reduces the amount of noise the receiver will pick up.
2) For AM at 100% modulation, 50% of the total transmitted power is in
the carrier (carrying no information), and 25% is in each of the (upper
and lower) sidebands, where they carry redundant information.
So the total power that's actually useful to the receiver is a pretty
small fraction of the total that is transmitted. The advantage of AM, of
course, is that it requires only a very simple receiver.
For suppressed-carrier SSB, all the radiated power is in the one set of
sidebands being transmitted. Assuming that in both cases the
transmitters draw equal power from the "wall outlet", then there's a
clear win for SSB. That advantage comes at the expense of a more complex
receiver, and the need for a more skillful operator to tune it.
The advantage of SSB is considerably more than the "almost double the
range" you mention -- more like 10 to 12 dB, where doubling would imply
3 dB.
Isaac
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