Engee documentation

FM Demodulator Baseband

Demodulates data modulated using the FM method.

fm demodulator baseband

Description

The FM Demodulator Baseband unit demodulates a complex input signal that has been modulated using the FM method, and returns a real output signal.

Ports

Input

# IN_1 — input FM modulated signal
scalar | vector | matrix

Details

An input FM modulated signal in the form of a scalar, vector or matrix. In the case of a matrix, each column is processed as an independent channel.

Data types

Float64.
Complex numbers support

Yes

Output

# OUT_1 — demodulated signal
scalar | vector | matrix

Details

Demodulated signal as a scalar or vector. If the output is a scalar, its value is an integer. If the output is a vector, it is a vector of integer or binary numbers.

Data types

Float64.
Complex numbers support

No

Parameters

Main

# Frequency deviation (Hz) — demodulator frequency deviation
Real number

Details

The demodulator frequency deviation, in Hz, given as a positive scalar. The system bandwidth is equal to twice the sum of frequency deviation and signal bandwidth.

Default value

75e3
Program usage name

FrequencyDeviation
Tunable

No
Evaluatable

Yes

Extras

*Algorithms.

The frequency modulated bandwidth signal, , is specified as:

where

  • - carrier amplitude;

  • - carrier frequency;

  • - baseband input signal;

  • - frequency deviation in Hz.

Frequency deviation is the maximum shift from in one direction, given that τ .

The baseband FM signal may be derived from a bandwidth representation by downsampling the bandwidth signal at such that:

Removing the component at from leaves a representation of the baseband signal, which is specified as:

The expression for can be rewritten as , where .

The expression ] thus means that the input signal is a scaled version of the phase derivative, .

To recover the input signal from , use a basic delay demodulator as shown in this figure.

fm demodulator baseband 1

See also

  1. FM Modulator Baseband

References

  1. Hatai, I., and I. Chakrabarti. "A New High-Performance Digital FM Modulator and Demodulator for Software-Defined Radio and Its FPGA Implementation." International Journal of Reconfigurable Computing (December 25, 2011): 1-10.

  2. Taub, H., and D. Schilling. "Principles of Communication Systems. McGraw-Hill Series in Electrical Engineering," 142-55. New York: McGraw-Hill, 1971.