On Sun, 03 Jan 2010 13:07:26 -0600, Lostgallifreyan
wrote:

If you look at that PDF you'll see the 15' whip antenna is directly connected
to ground through 80 turns of wire on a ferrite toroid. I might add a spark
gap in parallel as that wire is not a high current path. So long as it is
much more likely to go to ground rather than along the line in to the house,
I'll have done what I'm supposed to do. The trouble would only exist (other
than unpreventable natural excesses) if it were evident that I had not done
this.

Yes, it is a grounded design. The folded monopole is simpler, however
and you can deal with matching identically. 80 turns of wire on a
ferrite toroid is going to test the limits of self-resonance, poor Q,
and efficiency across so large a span of frequency.

Well, a ground rod isn't going to cost much, and making and breaking
connections to it is one of the easiest and cheapest things I'll be able to
do, so I'll test that empirically when I'm ready. I won't try to predict it
now. Whenever I find some new ground noise problem in anything I do here, I
usually manage to isolate it and solve it acceptably within an hour or less,
so I'll trust my chances. Usually the purpose hasn't been for RF, but quite
often the sources did involve RF too so my instincts might help me more than
my knowledge.

Sounds like a lot of faith and work that will eventually require more
investment in faith and work. A shallow buried radial system would
puncture these superstitions.

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.


Well, I did think of that. And I didn't state it because I didn't know for
sure.

That's why I tossed that hand grenade into the mix.

As I imagine that local RF couplings from various digital devices might
place small currents on the local ground, I imagine that grounding a shield
at the remote ground makes sense.

It does, but that isn't the complete solution if you don't choke the
feedline. Again, ground is not found in the rod you drive into the
earth (which, by the way, will take years to "cure" to the ground
resistance you hope to achieve).

Doesn't matter to me though. It's far
easier and faster to experiment than to try to predict because there are only
two ways to try.

This is about experience. You will find (and I have found) damn
little reference to grounding by connection to the earth. It has
taken me years to accumulate these rare references. They have been
topics of discussion here (use google to search the archives).

Dallas Lankford directly states that no shield is even
required, and I doubt he'd have said that if he couldn't demonstrate it, and
as that line is a two-wire loop that has no direct contact with anything, it
should reject any common mode noise that hits it.

Many people make direct statements (hard not to in this environment
that relies on textual postings). You need to find a better source of
study material as it relates to Common Mode. Twin line suffers it
equally. Again, all such discussion arrives through where the source
and load are, not in the line between.

Even in audio this matters
because the same method is used to reject RF pickup on audio lines. I think
some people persist in baluns instead of op-amp common mode rejection specs
for this reason, despite the chances of modest distortion in audio bands from
the transformers used. Not entirely relevant but it illustrates how people
can find themselves choosing between two less-than-ideal circumstances for
best effect.

You are confusing topics here. BalUns and what are properly chokes
are not always the same, although their discussion is often co-mingled
to considerable misunderstanding. BalUns are NOT transformers as you
might imagine from the point of view of AF. It is regrettable that
BalUns are called transformers, as their full nomenclature is
Transmission Line Transformer - meaning the transform of Z by
transmission lines that have their ends isolated through choking
action.

Lest that sound too obtuse: The best BalUns do not operate through
magnetic flux linkage. You are not in Kansas anymore.

I understand that noise context matters for a real attempt to plan for it,
but that's far more difficult that presenting the basic antenna scheme.

Hence the novelty of individual threads. Noise arrives in the same
manner as RF - it is indistinguishable until you put on your
headphones. Noise is what arrives between your ears.

In regards to this last epithet, I noticed that Lankford wrote a piece
about quad detectors. I first designed one 40 years ago and the
critical component missing in Lankford's discussion (and probably from
many such discussions surrounding this method of detection) is that
the two channel output of a phase quadrature detector is meant to
drive STEREO headphones so that the last step of detection is found in
the brain's capacity to differentiate noise from signal.

73's
Richard Clark, KB7QHC