Different modulations:

There are 5 main types of modulations in analogue radio:

- FM (Frequency Modulation)
- AM (Amplitude Modulation)
- BLU (band or less)
- CW (Telegraph)
- FSK (RTTY)

• Modulation FM:

Modulation FM (Frequency Modulation) is to vary the frequency of the carrier at a rate of the audio signal. The frequency of the carrier frequency varies with the audio signal amplitude and the rate of variation of the carrier frequency varies depending on the frequency of the audio signal.

                   There are two types of bandwidth FM:

• WFM mode (Wide Frequency Modulation) broadcast by TDF for example Radio France, Fun Radio, RMC, NRJ, Europe2…
• NFM Mode (Narrow Frequency Modulation) is suitable for the reception of t Professional Firefighters transmissions for example or the DDE, EDF, SNCF…

• Modulation AM:
  Modulation AM (Amplitude Modulation) consist in vary the amplitude of the envelope of the carrier wave to the rhythm of the audio signal. In AM bandwidth is approximately 5 kHz.

Today AM modulation is widely used in aviation (between 108 and 136MHz and 136 to 144MHz for the military aircraft).

 

 

• Modulation BLU:
  The SSB modulation (Single Side Band) is an AM modulation performed on one side of the carrier. We talk about BLU-USB when the upper side is modulated and we talk about BLU-LSB when it is the lower side. USB = Upper Side Band and LSB = Lower Side Band. Today, BLU is only use by some wired systems today.
• Modulation CW = morse code :
  The morse code,  consist to transmit a text with a series of short and long pulses. (Invented in 1835 by Samuel Morse).  Each pulse frame corresponds to a number or a letter.
  The morse is still used today, especially by radio amateurs.
  It is also used to identify radios repeater.

Morse Signals are generated through software which can operate under Windows or under Linux. The software CWget and Multipsk are most currently used today.

• FSK Modulation:
  Modulation FSK (Frequency Shift Keying) is used in RTTY (Radio Tele TYpe) for the transmission of digital ballots coded in binary. Bit 0 is represented by an audio signal from 500 Hz to 1 kHz. Bit 1 is represented by an audio signal from 1 to 2 kHz.