What is NBFM?
What is NBFM?
NBFM stands for Narrow Band Frequency Modulation.
What is the range of modulating frequency for the NBFM?
For NBFM, the FM modulation index must be less than 0.5, although a figure of 0.2 is often used. For NBFM the audio or data bandwidth is small, but this is acceptable for this type of communication. Narrowband FM is widely used for two way radio communications.
What are modulation index and sidebands?
The FM sidebands are dependent on both the level of deviation and the frequency of the modulation. For small values of modulation index, when using narrow-band FM, NBFM, radio communication systems, the signal consists of the carrier and the two sidebands spaced at the modulation frequency either side of the carrier.
What is Carson’s formula?
The formula that calculates this bandwidth is called CARSON’S RULE. To calculate the CARSON’S RULE bandwidth occupancy of this signal, add the highest audio frequency to the peak deviation (15KHz + 75KHz = 90KHz), then multiply by two to include both the upper and lower sideband (90KHz X 2 = 180KHz).
How is the NBFM converted into WBFM?
To convert a NBFM to WBFM we have to increase the frequency deviation and carrier frequency of the NBFM.
What is the condition we needed to achieve NBFM?
The most important condition is that the input signal to noise ratio exceeds a threshold value. Below this threshold, the signal to noise output deteriorates rapidly, and for low inputs the signal to noise is worse than SSB. In amateur use, narrow band FM (NBFM) is used.
What is the transmission bandwidth of NBFM?
The envelope contains residual amplitude modulation and , therefore, varies with time. an AM signal and NBFM signal is that the algebraic sign of the lower side frequency in the NBFM is reversed. Thus a NBFM signal is essentially requires the same transmission bandwidth (i.e 2 ) as the AM signal.
What is the difference between NBFM and WBFM?
When spectrum efficiency is important, Narrowband FM (NBFM) is used but when better signal quality is required, Wideband FM (WBFM) is used at the expense of greater spectrum usage. The term WBFM is used in applications where the modulation index is equal to or larger than 1.
When to use a frequency multiplier for NBFM?
If NBFM wave whose modulation index $\\beta$ is less than 1 is applied as the input of frequency multiplier, then the frequency multiplier produces an output signal, whose modulation index is ‘n’ times $\\beta$ and the frequency also ‘n’ times the frequency of WBFM wave.
How is the modulation index of a NBFM wave calculated?
Where, ‘n’ is the multiplication factor. If NBFM wave whose modulation index β is less than 1 is applied as the input of frequency multiplier, then the frequency multiplier produces an output signal, whose modulation index is ‘n’ times β and the frequency also ‘n’ times the frequency of WBFM wave.
What is the standard equation of FM Wave?
Generation of NBFM We know that the standard equation of FM wave is s (t) = A c cos (2 π f c t + 2 π k f ∫ m (t) d t)
How is the generation of WBFM wave done?
The block diagram of generation of WBFM wave is shown in the following figure. This block diagram contains mainly two stages. In the first stage, the NBFM wave will be generated using NBFM modulator. Earlier we have seen the block diagram of NBFM modulator.