On Sun, 03 Jan 2010 05:26:32 -0600, Lostgallifreyan
wrote:



Most people I ever came across asserted the importance of a ground
rod local to the antenna to couple with the local water table which is as
close as most ever get to the ocean unless they really like getting their
feet wet while they sit around at home.

In fact, this almost always NEVER happens. Skin effect defines the
layer depth of RF in ground. An 8 foot rod is like a splinter when
you are trying to harpoon a Blue Whale.

Ground rod engineering has been discussed in this forum to great depth
(pun intended, or not). The rods are as well understood as water
witching forks. In the HF region, single or several rods have no
practical RF use whatever. Above HF, absolutely no one gives them any
thought.

The proximity is as close to the
point where they want to pick up RF as they're going to get, and means less
noise from buildings full of electrical stuff picked up on metal between
antenna and whatever other ground might be provided elsewhere. This has been
the ONE common factor in pretty much everything I've seen on land-based AM
reception. Anything that directly appears to negate that advice makes it hard
to know what to trust, and certainly needs to be clearly explained.

When you can't do anything else that is effective, a ground rod seems
like more than enough. It is certainly a need for safety's sake,
especially when your vertical could be a lightning magnet. Consider
that same antenna: is it directly GROUNDED? Or is it floating? If
ground is a panacea, I bet most of your advisors immediately isolate
their antenna from it. One has to wonder about faith....

Either design works with equal efficiency. You simply need a coupling
system to the grounded antenna design. One method is using a folded
monopole. Other methods abound (which are often confined to yagi
driven element discussion, but are eminently applicable here).

The moment I try to connect to a system that includes a computer,
mixer, multiple supply grounds, as mine does, I'll be using a local
service ground and improving it the same as I would for audio, though it's
currently ok for that, at least. It already uses a star grounding system
where possible, as recommended by audio studio designers and others. There's
actually a supply ground rod outside the front door too, which presumably
helps more than the original wiring 15 years ago which didn't have that. (But
note below, where I mention isolation).

The Star system is great for exactly as you understand and describe
it, but for antenna applications that remote ground could act as a
suicide adapter if it does not have its own path to the service
ground. Yes, this violates the star, but when path lengths include a
lot of resistance and leakage current, voltages can become
considerable when you supply a new avenue through your home. This is
the story of the classic ground loop.

Hence the star network I mentioned, advised for audio setups.. It's kind of
why I wonder about what many suggest, grounding a coax at both ends, and even
in the middle if you want, and certainly to bury it. More importantly it's
why the Dallas Lankford design appeals to me. Isolation baluns that transfer
energy rather than use direct contact coupling look like a good way to avoid
the ground problems while also avoiding local noise pickup because the twin
cable will have good common mode rejection as it passes into the electrically
noisy bulding. (Though I can't help wondering if Dallas Lankford also tried
balanced microphone cable with a screen grounded at one end, just to see what
happened) Such methods have long been used in audio; is RF below 30 MHz
really so different in this case? So long as that line doesn't have dire
resonances of it's own, isn't attenuation the only big risk? Dallas Lankford
certainly thinks it works after working with it for at least 2 years. He says
that if you do it as described it will be low noise. (As opposed to
'reducing'). I don't think he's claiming any means of reduction, just saying
it's lower relative to inherently noisier systems, if wired as decribed.
Based on what I know, the claim seems good.

I'm not familiar with Dallas Lankford, but isolation and shielding
techniques are topics I have visited professionally throughout the
years and they are not simple. Without a concommitant discussion of
the noise source, one wrong ground selection can wipe out all pursued
benefits. Let's revisit one of your statements above:
balanced microphone cable with a screen grounded at one end
Which end? Any choice stands an equal chance of being the wrong
choice.

73's
Richard Clark, KB7QHC