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Old 3rd January 2011
  #8
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Quote:
Originally Posted by RHSuperfly View Post
At night, radio and television transmitters power down a bit because for some reason related to the sun rf waves travel further at night, so for commercial broadcasters to avoid having their transmissions crossover into another broadcaster's territory they all power down a bit.
Um... no, not all radio and TV stations change power at night. All FM and TV stations are required by law to remain at their licensed power, no greater than +5% or - 10%, 24 hours a day, no exceptions. These days power control is automatic, so it's more like within 1%.
Quote:
Originally Posted by RHSuperfly View Post

RF is on all ac mains and does travel into most gear to some extent, though not much, and you won't hear the rf anyway unless something is malfunctioning is a very particular way. Nevertheless, the rf can raise the noise floor a bit and interfere with AtoD conversions.
Again, no. RF is not on all AC mains. In fact, most AC mains have no significant RF on them, and what little some may have is easily filtered off. And incidentally, it doesn't take a malfunction to make RF audible. It does take extremely hot RF into a good design, or much less into a bad design that can demodulate RF without a "malfunction". To design an RFI proof audio device costs extra money. It's done all the time, gear made to operate at a radio station is RF immune. But you pay for it. It's possible that RF could bother A/D converters, but not the levels coming through the power lines, sorry, no chance. Ever looked at a power line with an RF spectrum analyzer? I have. The typical RF on power lines is 80 to 100dB below the power sine wave, and that's before it hits even the most basic filtered power strip, or even the filtering inside a device. There are some exceptions, but very few, and they are very specific to locations, like very close to high power transmitters.

Quote:
Originally Posted by RHSuperfly View Post

Mains really do quiet down after 2am as by then most people are in bed, businesses are all closed (most of them) and most internet surfing has also gone to bed.

Cheers

As to the last statement, people going to bed has nothing to do with line noise, and neither does internet surfing. Business use of power may have an impact on line noise, but again, it's highly case-specific, and not correct to generalize that the lines get quiet after 2am. I know of at least one factory that used its high power thermal forming machines only after midnight because the power cost is lower off-peak.

Let's not propagate mythology, it really hurts everyone.