- #36
Averagesupernova
Science Advisor
Gold Member
- 4,573
- 1,317
@Silly Questions I've had a hard time figuring out how to reply to a lot of your posts. It's obvious you are putting thought into this but it seems that you have a little bit of knowledge and start making assumptions after that.
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You speak of fidelity. That is a very loosely defined word. I can have a recording studio that captures sound well above 40 khz. Then 'dumb it down' and cut off all the frequencies above the range of human hearing. Have I reduced the fidelity of the signal? Clearly I have taken away signals but considering I never heard them in the first place the fidelity remains acceptable. Same way with attenuation. The signal can be attenuated, then amplified to the intended level. As long as the signal did not get reduced to the point that the noise floor becomes audible we have an acceptable signal fidelity-wise. Again, fidelity being a loosely defined word.
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Now considering this wind mill blade thing chopping up the signal. The actual truth is that you cannot do anything non-linear to a sine wave without creating new frequencies. You are not just varying the amplitude of the carrier with a power control knob on a transmitter when you rapidly move it back and forth. You create sidebands. Yep, new frequencies. If you diddle the power control knob at a rate of 10 cycles per second, you have sidebands 10 Hertz either side of the carrier, and the amplitude of the carrier itself remains unchanged on a spectrum analyzer. Difficult to believe, but it's true. Now when you use the windmill blades to reduce the signal with each passing blade, think of it as modulating both the carrier as well as the sidebands. Suppose a given rpm of the blade puts us at 100 Hertz. Every signal will be affected. The windmill doesn't care which is the carrier and which is the sideband(s). Each sideband as well as the carrier will now have side bands 100 Hertz either side. Confused even more?
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You speak of fidelity. That is a very loosely defined word. I can have a recording studio that captures sound well above 40 khz. Then 'dumb it down' and cut off all the frequencies above the range of human hearing. Have I reduced the fidelity of the signal? Clearly I have taken away signals but considering I never heard them in the first place the fidelity remains acceptable. Same way with attenuation. The signal can be attenuated, then amplified to the intended level. As long as the signal did not get reduced to the point that the noise floor becomes audible we have an acceptable signal fidelity-wise. Again, fidelity being a loosely defined word.
-
Now considering this wind mill blade thing chopping up the signal. The actual truth is that you cannot do anything non-linear to a sine wave without creating new frequencies. You are not just varying the amplitude of the carrier with a power control knob on a transmitter when you rapidly move it back and forth. You create sidebands. Yep, new frequencies. If you diddle the power control knob at a rate of 10 cycles per second, you have sidebands 10 Hertz either side of the carrier, and the amplitude of the carrier itself remains unchanged on a spectrum analyzer. Difficult to believe, but it's true. Now when you use the windmill blades to reduce the signal with each passing blade, think of it as modulating both the carrier as well as the sidebands. Suppose a given rpm of the blade puts us at 100 Hertz. Every signal will be affected. The windmill doesn't care which is the carrier and which is the sideband(s). Each sideband as well as the carrier will now have side bands 100 Hertz either side. Confused even more?