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Old 07-28-2013, 11:35 AM
kj6zd kj6zd is offline
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<p style="text-shadow:3px 3px 3px green;colorlive;">AM versus FM modulation</p>
Quote:
I didn't know that the envelope on AM became audibly quieter the farther you get away from the transmitting station. I didn't think that would matter to a radio.
Remember what you may have learned about the two modulation types?
Frequency modulated signals do NOT change the Amplitude of the transmitted signal including the information itself. Therefore, they will always be at maximum amplitude e.g. max. power.

Amplitude modulated signals will change the amplitude in the rythm of the modulated voice. Therefore the Amplitude may be higher or lower at certain words / vocals. In other words the amplitude is moving between very low and maximum power, depending on the information that is modulated onto the carrier. Look at a SSB signal which is basically AM with surpressed carrier.
AM signal are modulated around 6 kHz (the mirophone amplifier will largely contribute to this) in Air communication this may not be enough or it is actually lower to compensate for background noise, remember they sit inside an airplane.
Thats mainly the reason why the signal appears to be a lot lower in level as an FM signal.

Cheers!
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