---
tags: [radio, ham-study]
---

# Single Sideband Modulation

With [AM-modulated transmission](./Frequency_modulation.md), "sidebands" are
created just below and just above the carrier frequency known as the upper and
lower sidebands (USB and LSB, respectively).

AM radio stations typically transmit on both sidebands. That is to say, they use
the full available bandwidth. However the two sidebands are copies of each
other.

This is not technically necessary, however. It is possible to transmit by just
using a single sideband. This is more efficient and means you are focusing your
power to transmit a single frequency.

The formula for the generation of the full audio signal is:

$$
\text{USB: } f_c + f_m \\
\text{LSB: } f_c - f_m \\
\text{Carrier: } f_c
$$

![Standard AM transmission](../img/standard-am-transmission.png)

The standard process of transmitting AM:

- Audio signal multiplies with carrier in accordance with formulae
- Two sidebands are created (USB, LSB)
- All three components are transmitted

![Single sideband transmission](../img/single-sideband-transmission.png)

With SSB:

- Audio signal multiplies with carrier in accordance with formulae
- Two sidebands are created (USB, LSB)
- A filter removes the carrier and one sideband
- Only one sideband (USB or LSB) is transmitted

> Crucially, this is possible because the carrier wave frequency is not needed
> for transmission and receiving. It is only needed in order to get the audio
> signal (_f_m_) up to the transmitter frequency ready to transmit. But it it is
> kept in during normal AM transmission.
