[Lowfer] NC Booming in on ground wave

[Dale Parfitt]

John Andrews wrote:

> Here's another thought.
>
> The output of a receiving antenna is the vector sum of the various signals
> that arrive at the antenna. For LF purposes, we commonly think simply of a
> desired signal coming by surface or sky wave, and all sorts of noise. The
> noise may atmospheric and arriving in the same way, or may come from the
> "near fields" of noise from local conductors. But things are not always so
> simple. Long conductors near the antenna can re-radiate the desired signal
> as well. And vectors being what they are, the re-radiated component may
> subtract from the desired signal. It MAY also add, but Mr. Murphy seems to
> prefer subtraction.
>
> For example, taking AM broadcast field measurements in an urban or suburban
> area is a major exercise in walking around trying to find why the signal
> isn't as strong as you expected. Re-radiated signals from power lines, metal
> fences, buried pipes and so forth can have a major effect on the readings.
> Even with those shorter wavelengths, moving 20 feet or so can make a big
> difference. (Remember that you are usually dealing with the near-fields of
> those re-radiated signals.)
>
> If you drive on a country road with overhead power lines in an area with not
> too many other conductors, you will frequently notice peaks in a
> medium-to-weak AM signal that occur every half wavelength. Or it may be
> easier to notice the "valleys" that occur a quarter wave later. This is
> coming from the vector sum of the desired signal plus the re-radiated signal
> from the power lines.
>
> My point is that unusual effects may occur if you put your receiving loop
> near other conductors. Mounting it on a steel tower would seem to be an
> invitation to odd behavior, though some of it may be positive as far as the
> desired signal is concerned. And since those conductors are also potential
> noise sources, you may be limiting your results. If you are lucky to have
> enough land at your disposal, I'd always suggest locating the RX loop as far
> from conductors as possible.
>
> John A.
>

Hi John,

Utilities are underground here so that should not be an issue- but on the
reradiation question; how long a conductor are we talking about for reradiation
to occur? I seem to recall Dex saying he had reradiated noise from nearby guy
lines.

Dale W4OP