The man knoweth of what he speaks.
Bob, K4TAX
----- Original Message -----
From: "Stuart Rohre" <rohre@arlut.utexas.edu>
To: "Discussion of Ten-Tec Equipment" <tentec@contesting.com>
Sent: Tuesday, June 28, 2005 2:27 PM
Subject: Re: [TenTec] RFI question for Orion and other TT rigs
> Absolutely RIGHT Bob,
>
> That hams need to understand the difference in why you use a ground rod
> and
> the other grounds in radio. (Rod-Electrical safety only, static discharge
> ground for arrestors).
>
> And the Radials- base of short quarter wave or less verticals, or
> counterpoise, (above ground radial). Is an RF ground.
>
> The counterpoise in shack- quarter wave insulated wires for each band, to
> help a shack that is raised physically a quarter wave or more above a
> physical RF ground re-establish a low RF impedance on the rig chassis.
> -Is an RF high potential control conductor.
>
> And no radials needed: (antenna is complete RF wise)- (half wave
> verticals,
> horizontal balanced antennas with center feed, beams, Moxons, etc.)
>
> Note off center antennas impose an imbalance that may need counterpoise.
> OCF's, Carolina Windom, and the original Windom are thus unbalanced by
> virtue of unequal flat top conductor lengths.
>
> And physical ground itself. Is NEVER a good RF ground alone. Only in
> extraordinary cases will driving a ground rod help with an RF problem.
> More
> than likely, the length of conductor you added, to reach the rod, is
> acting
> as a counterpoise wire, moving the high RF point off the rig chassis and
> out
> the shack to the end of the conductor near the rod.
>
> Many places like New England, Southwest, Tropics, Deserts, have terrible
> RF
> character in their local earth ground, and cannot be relied on for RF low
> impedance---no matter how many ground rods you might sink.
>
> Hams need to realize that to be a good RF ground, the earth would have to
> be
> a metallic low impedance conductor of RF. "Dirt don't do it".
>
> Those who are so concerned about running around driving ground rods to
> solve
> RF problems, should answer the question:
>
> -Where do you drive the ground rod for a spacecraft in orbit? Yet their
> radios work from HF to microwaves just fine.
>
> The ground rod is seldom a significant portion of a wavelength at HF
> frequencies, thus will be a poor fraction of a wavelength counterpoise.
>
> Driving ground rods vertically is often impossible to adequate depth for
> lightning protection. Digging a trench and laying out a circumferential
> ground wire around the house/ station will do as well. 200 feet of no. 10
> bare has been calculated by Austin Energy here, to equal the best 9 foot
> ground rods. Eighteen inches deep is doable at most sites, and is
> completely adequate depth. For lightning protection you want current
> spreading, so conductor area in contact with soil becomes paramount.
>
> -Stuart Rohre
> K5KVH
>
>
>
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