Wideband FM is to be generated from narrowband FM using the indirect method of Figure 4.10....

 

Transcribed Image Text:

Wideband FM is to be generated from narrowband FM using the indirect method of Figure 4.10. For the narrowband FM, fe1 = 125 kHz and Af, = 30 Hz. For the desired wideband FM, f. = 80 MHz and Af = 48 kHz. (a) Suppose the largest multiplication factor allowed for an individual multiplier is 5, and n = nz. Complete the design of the indirect WBFM generator by specifying the constituent multiplying factors for n, and n2, and by specifying the two possible local oscillator frequencies. (b) Repeat part (a) if only frequency doublers and triplers are allowed, n and ny should be as close in value as possible but are not necessarily equal, and the frequency deviation of the WBFM may be higher or lower than, but should be as close as possible to, the desired value of 48 kHz. (c) Determine a new value of Af, such that with the values of n and na found in part (b), the frequency deviation of the WBFM will be the desired 48 kHz. fa fa Frequency Afa Multipliers f'a fo Frequency Af Narrowband Ai Frequency Modulator Multipliers in Cascade (*n) Frequency in Cascade (*n,) Converter m(1) WBFM A cos 2nf A, cos 2n fiot Crystal Oscillator Local Oscillator Figure 4.10. Indirect method of generating wideband EM. Wideband FM is to be generated from narrowband FM using the indirect method of Figure 4.10. For the narrowband FM, fe1 = 125 kHz and Af, = 30 Hz. For the desired wideband FM, f. = 80 MHz and Af = 48 kHz. (a) Suppose the largest multiplication factor allowed for an individual multiplier is 5, and n = nz. Complete the design of the indirect WBFM generator by specifying the constituent multiplying factors for n, and n2, and by specifying the two possible local oscillator frequencies. (b) Repeat part (a) if only frequency doublers and triplers are allowed, n and ny should be as close in value as possible but are not necessarily equal, and the frequency deviation of the WBFM may be higher or lower than, but should be as close as possible to, the desired value of 48 kHz. (c) Determine a new value of Af, such that with the values of n and na found in part (b), the frequency deviation of the WBFM will be the desired 48 kHz. fa fa Frequency Afa Multipliers f'a fo Frequency Af Narrowband Ai Frequency Modulator Multipliers in Cascade (*n) Frequency in Cascade (*n,) Converter m(1) WBFM A cos 2nf A, cos 2n fiot Crystal Oscillator Local Oscillator Figure 4.10. Indirect method of generating wideband EM.