[RFI] 30m Interference

[Jim Brown]

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