Modes

Modes SIMPLy explained

It's been noticed that a some CB operators today lack a clear understanding of the distinction between "modes" and "bands." This issue is particularly common here in the UK, where most operators have had very little exposure to MultiMode transceivers in the early legal days of CB radio and perhaps are only familiar with the standard UK 40 channels or are limited to single-mode radios—specifically the 27/81 27MHz FM units that were legalised.

Even after explaining the differences between modes and bands, I find myself having the same conversation repeatedly with operators who struggle to grasp these different modulation types.

This confusion likely originates from a common misconception with broadcast radio receivers, particularly small transistor radios with band switches labeled "AM/FM." While these switches do indeed change bands, the labelling refers to modulation modes rather than frequency bands.

Understanding the Different Modes:

Figure 1 below shows how modulation is presented for each type of mode used typically in radio.

AM (Amplitude Modulation): The carrier wave's intensity varies in accordance with the audio frequency. This modulation is transmitted as DSB (Double Side Band). Essentially, the carrier serves as a foundation for the modulation, with intensity changes resulting from how the audio frequency is applied to the carrier wave.

FM (Frequency Modulation): This operates similarly too AM, but instead of amplitude changes, the carrier frequency deviates in response to the imposed modulation. Again, the carrier primarily supports the modulation while maintaining the same DSB pattern.

SSB (Single Side Band): This is essentially AM with rectified audio, using either the upper or lower sideband. The process is both simple and ingenious. However, unlike AM and FM, the carrier is suppressed and doesn't form part of the actual transmission.

Reception Requirements:

Each mode requires different detection methods at the receiver:

• AM: Simple diode detector

• FM: Discriminator circuit

• SSB: Product detector

I hope this clarifies the concept of modulation modes. I'd be interested to hear from others who've encountered similar gaps in understanding among 11m operators, particularly regarding these fundamental mode differences.

73's DE Will 26AM081