Topband: Noise and ground loops
Sat, 14 Dec 2002 06:04:04 -0500
> I do not normally share the model I use for the K9AY loop, since
> it knowingly violates some NEC-2 modeling rules in order to obtain a
> reasonable correlation to observed behavior. I use it solely to
> evaluate the radiation pattern of the loops. NEC-2 should not be
> trusted to evaluate anything connected to, or lying on, ground.
If the model is too sensitive through violation of guidelines, it can
not be used to predict any interaction with anything Gary. But all
that aside, there are very logical and reasonable engineering
criteria for isolating grounds in noise-critical systems.
Good engineering practices always dictate we avoid common mode ground
With that in mind, I would never consider having a receiving antenna
of any type share a signal ground with any potential noise source.
Not speaking of your antenna, but I've seen dozens of antennas that
actually work because of ground loops or common mode currents that
the designers! For example, even small voltage probes are a big
problem with common mode.
It is obviously a very commonly missed problem, and my advice is
intended to draw focus to the problem on ALL antennas.
> While common mode noise can be a significant issue in some cases
> (e.g. Beverages, where their length supports efficient coupling), I
> think it is overstated for most practical installations. At radio
> frequencies (as compared to 50/60 Hz), radiated noise will almost
> always swamp out common-mode (conducted) noise.
My experience is otherwise, unless the antenna is a long distance
from common-mode noise sources or conductors carrying noise. The
same noise that follows power lines for dozens of miles will only go
a few hundred feet without a direct conductor path.
Particular antennas aside, it is a big mistake in a cluttered RF
environment to connect the power line and house grounds directly to
low-noise antenna grounds with any antenna. In Rockdale county, my
biggest problems were keeping "noise" from following grounds out to
my antennas, thats where I learned most of my lesson.
73, Tom W8JI