Hi Joel,
Given an equal noise power distribution across the whole 6 kHz, using a
3 kHz filter should cut the total received noise power in half. All of
the TX power (both carrier and sideband) with SSB-AM is inside that 3
kHz. Same transmit power, half the received noise, resulting in a 3 dB
improvement in SNR using SSB-AM versus DSB AM.
By not transmitting the carrier, twice as much power can be put into the
one sideband resulting in an additional 3 dB SNR improvement. Thus a
total of 6 dB improvement in SNR from full carrier DSB AM to no carrier SSB.
All of the above assumes the same peak power capability of the AM and
SSB transmitters.
In practice, using the same amount of iron, if built properly an SSB
transmitter can be made to produce more peak power than an AM
transmitter, because of the lower duty cycle, not having to generate
that 100% duty cycle carrier. So, given the same mass transmitter, SSB
has an additional "virtual" 3 dB advantage over AM.
On the other hand if you use CW confined to a couple of hundred hertz
bandwidth and power amplifiers running in class C (along with the
necessary filtering to reduce harmonics to an acceptable level) you have
an SNR improvement of 10 or 20 dB compared to DSB-AM. This requires a
skilled operator at the receiving end, which requires effort, and is
therefore out of style these days.
Ken N6KB
joel hallas wrote:
> The classic SSB-AM signal was that generated in the Collins KWS-1 of 1956.
>
> I agree, it's not exactly a transceiver, but another example of that
> kind of signal.
>
> If received in a receiver with 3 kHz filter, the SNR of such a SSB-AM
> signal should be the same as with a DSB-AM signal of the same carrier
> level in a 6 kHz wide receiver. It also takes up less spectrum.
>
> Joel Hallas, W1ZR
>
>
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