Subelement A: — Topic :
Question 6A391
Element 6 (Radiotelegraph)If a 1500 kHz radio wave is modulated by a 2000 Hz sine wave tone, what frequencies does themodulated wave contain?
Explanation
When a radio wave (the carrier) is amplitude modulated (AM) by an audio signal (the modulating tone), the resulting modulated wave contains three primary frequency components:
1. **The original carrier frequency (Fc):** This remains at 1500 kHz.
2. **An upper sideband (USB):** This is the carrier frequency plus the modulating frequency.
2000 Hz is equal to 2 kHz.
So, USB = 1500 kHz + 2 kHz = 1502 kHz.
3. **A lower sideband (LSB):** This is the carrier frequency minus the modulating frequency.
LSB = 1500 kHz - 2 kHz = 1498 kHz.
Therefore, the modulated wave contains frequencies at 1500 kHz, 1502 kHz, and 1498 kHz, making option A correct. Options B and C are incorrect because they use the wrong units (MHz or Hz) for the radio wave frequencies.
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