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#1
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Cecil Moore wrote:
Richard Harrison wrote: Richard Fry wrote: "Not so. You confuse receivers and transmitters." FM transmitters often use Class C amplifiers and frequency multipliers on the modulated signal. An AM signal can not be amplified by a Class C amplifier because of severe distortion of the modulated signal. In FM, amplitude distortion is irrelevant no matter where it occurs, receiver or transmitter. The recovered audio will sound just fine. It`s one of the many advantages of FM. The question seems to be: If an FM transmitter's output signal is not a reasonably pure sine wave, is a low-pass filter used between the transmitter and antenna to reduce the harmonics? How can a filter filter correctly when its input is terminated in an indeterminate impedance? 73, Tom Donaly, KA6RUH |
#2
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How can a filter filter correctly when its input is terminated in
an indeterminate impedance? ============================ No problem! The frequency response of a filter, input to output terminals, is independent of the source resistance. |
#3
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Reg Edwards wrote:
How can a filter filter correctly when its input is terminated in an indeterminate impedance? ============================ No problem! The frequency response of a filter, input to output terminals, is independent of the source resistance. That may be true in the Danelaw where you live, Reg, but not in the rest of the universe. Imagine a circuit consisting of a voltage source in series with a source resistance followed by a shunt capacitance in parallel with a load resistor. Write the output voltage equation for this circuit. Now, replace the source resistance with a short. Write the output equation for _this_ circuit. Compare the two equations. Are the frequency responses the same? Now use an indeterminate impedance for the source resistance. Can you tell what the voltage output of this circuit is? 73, Tom Donaly, KA6RUH |
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