Topband: Where to ground the Beverage feedline?
zr at jeremy.mv.com
Tue Nov 20 10:41:44 EST 2012
----- Original Message -----
From: "Tom W8JI" <w8ji at w8ji.com>
To: <topband at 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
> 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.
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