J
John O'Flaherty
- Jan 1, 1970
- 0
Radium said:Hi:
Lets say there is an AM station with a carrier frequency of 150 KHz.
What is the highest frequency of modulation that it can handle?
I think it depends on a bandwidth, and the exact limits, not a single
frequency. You could modulate a band extending from, say, 100 kHz to
120 kHz, with a 150 kHz carrier, producing a modulated band from 30 kHz
to 50 kHz. Then you could recover the original band at a receiver with
a local oscillator of 150 kHz. As long as there is no overlap of
frequency bands, there's no ambiguity or aliasing. This assumes the
frequency bands produced can be isolated with filters, which they can
in the case mentioned.
On the other hand, if you modulated a band from 20 Hz to 120 kHz with
a 150 kHz carrier, there would be no way to distinguish, and separate
by filters, all the frequencies coming out of the modulator. For
example, an input signal of 76 kHz in the input band would be present
in the output as 76 kHz (itself) and 74 kHz. A 74 kHz input would
likewise be present as 76 kHz and 74 kHz, and there would be no way to
separate the two signals.
In digital audio, the sample rate must be at least 2x the highest
frequency. What is the equivalent in analog AM radio?
You could go to just under 75 kHz, theoretically, but that's well
above audio in any case.