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FM Transmitters FCC Commercial Broadcast Specs f c : 88.1 – 107.9 Mhz, 200 kHz Spacing f c stability: +/- 2 kHz (+/-20 ppm) f m range: 50 Hz – 15 kHz (75uS.

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Presentation on theme: "FM Transmitters FCC Commercial Broadcast Specs f c : 88.1 – 107.9 Mhz, 200 kHz Spacing f c stability: +/- 2 kHz (+/-20 ppm) f m range: 50 Hz – 15 kHz (75uS."— Presentation transcript:

1 FM Transmitters FCC Commercial Broadcast Specs f c : 88.1 – Mhz, 200 kHz Spacing f c stability: +/- 2 kHz (+/-20 ppm) f m range: 50 Hz – 15 kHz (75uS pre-emphasis)  f c < 75 kHz (maximum carrier deviation) 100kW max (horizontal and/or vertical polarization) Direct FM using VCO f c, k o (Hz/v) VCO v m (t)f out vmvm koko fcfc

2 Frequency Multipliers f out = Nf in f in Unwanted Harmonics Desired Harmonic: N Frequency Multipliers also multiply phase, hence modulation index!

3 FM from PM …and vice versa k p (rad/v) fcfc Most analog phase modulators exhibit acceptable linearity only for |  thus m p/f < . We can create higher modulation index using a frequency multiplier. N Phase Mod Equivalent Frequency Modulator

4 PM from FM... while we’re at it. VCO Equivalent Phase Modulator

5 Narrowband FM m p/f ~0.5 > only 1 sideband Carrier (stationary) LSBUSB USB + LSB LSB USB USB + LSB Hey Bret, do you remember plain ol’AM? …do you remember anything? What if we were to delay the sidebands by  /2 ? FM Phasor 

6 Armstrong Method for WBFM

7 Reactance Modulator (Voltage Variable Capacitance) Linear!


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