On 6/11/2011 7:28 PM, J.Gordon Beattie, Jr., W2TTT wrote:
> I am
> generally concerned about any weak signal interference that could possibly
> be propagated beyond the local environment.
Most man-made noise that reaches our ham receivers is radiated by wiring
connected to the noise source and received by our antennas, just like
any other signal. And, just like any other radiated signal, it will
propagate by ground wave, sky wave, and all the other types of propagation.
When a band is dead (that is, when there is no skywave), we hear only
local noise. When the band opens, we skywave from millions of distance
sources that are individually weak, but add together and combine with
local noise to produce the total noise floor. It is entirely normal
for the skywave noise to increase by 10-20 dB when the band opens. If
you have a quiet QTH, it's common to see 10-15dB increase. If your
location is noisy, you might not even notice a change.
There's a nice discussion of this in the ON4UN book.
73, Jim K9YC
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