----- Original Message -----
From: "Tom W8JI" <w8ji@w8ji.com>
To: <topband@contesting.com>
Sent: Tuesday, November 20, 2012 9:00 AM
Subject: Re: Topband: Where to ground the Beverage feedline?
Um -- what did you say was the typical skin depth of soil at 2 MHz?
Somehow, I seriously doubt it was down that far. :)
Common mode suppression requirements depend on things:
1.) The sensitivity of the antenna to all signals, either bad unwanted
signals like noise or good wanted signals. This is the good signal and bad
noise power output of the antenna.
2.) The level of unwanted signals and noise fed down the feeder towards
the antenna.
3.) The ratio of series and shunt impedances along the system, but only
**if** the system has enough unwanted CM junk to overcome antenna signal
power.
For some reason beyond my understanding, I think we are going far over the
top of what is reasonable....and it is getting worse.
I was at a friend's house and he told me about installing very long bead
strings in Yagi antenna feeders. Please, let's all stop this needless bead
insanity and get back to some common sense.
Any conductor very near earth for a long distance has considerable
attenuation along the conductor. If it didn't, we could bury our NVIS
antennas or run longwires laid right on dirt with high efficiency. It's
all about ratios everywhere in the system, including the CM injected and
signal level sensitivity of the antenna.
I make enough measurements of antennas here every year, some right in my
driveway near noise sources, to know when something is getting overblown.
73 Tom
Its easy to see the attenuation; just compare a 160M dipole at 30-50' to one
on the ground and also compare resonance points.
On my rock pile its significant and crud pickup goes way down. In the desert
it may be less significant.
Carl
KM1H
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