48 lines
1.6 KiB
Markdown
48 lines
1.6 KiB
Markdown
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---
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tags: [radio, ham-study]
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---
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# Single Sideband Modulation
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With [AM-modulated transmission](./Frequency_modulation.md), "sidebands" are
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created just below and just above the carrier frequency known as the upper and
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lower sidebands (USB and LSB, respectively).
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AM radio stations typically transmit on both sidebands. That is to say, they use
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the full available bandwidth. However the two sidebands are copies of each
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other.
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This is not technically necessary, however. It is possible to transmit by just
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using a single sideband. This is more efficient and means you are focusing your
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power to transmit a single frequency.
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The formula for the generation of the full audio signal is:
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$$
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\text{USB: } f_c + f_m \\
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\text{LSB: } f_c - f_m \\
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\text{Carrier: } f_c
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$$
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The standard process of transmitting AM:
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- Audio signal multiplies with carrier in accordance with formulae
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- Two sidebands are created (USB, LSB)
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- All three components are transmitted
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With SSB:
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- Audio signal multiplies with carrier in accordance with formulae
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- Two sidebands are created (USB, LSB)
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- A filter removes the carrier and one sideband
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- Only one sideband (USB or LSB) is transmitted
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> Crucially, this is possible because the carrier wave frequency is not needed
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> for transmission and receiving. It is only needed in order to get the audio
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> signal (_f_m_) up to the transmitter frequency ready to transmit. But it it is
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> kept in during normal AM transmission.
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