On 4/30/11 8:40 PM, firstname.lastname@example.org wrote:
> I believe that the key question for you is whether your vertical is
> "ground mounted" or elevated mounting ?
> Assuming that it is ground mounted, radials which are placed on or below
> the ground's surface are detuned by the ground, therefore, the length is
> not critical. Get as many radials down as possible, each as long as
> possible. Rule of thumb is that a minimum of 20 fifty foot long radials
> will get you going in the right direction. Additional grounding through
> 8 or 10 foot long ground rods needs to be in place as well for both
> lightning protection and as part of the RF ground system. Again, the
> rule of thumb is a minimum of 1 ground rod, however, 4, placed around
> the base of the antenna would be ideal.
> Hope this helps.
if you look at the current distribution in the soil, radials longer than
the radiator is tall don't do much good.
Think of taking this to an extreme.. say your radiator was 6 feet long..
all the return currents are going to be right there... there's not much
near field, say, 20 feet away.
An example of this is doing a tesla coil.. they're running at 100kHz or
so, so the height of the coil is very, very much shorter than a
ground rods don't do much for RF performance (in fact, that was one of
the first validations of NEC-4..)
They do help for lightning protection, but I would think that for a
single 30 foot high mast, you're just not going to need all that much of
a lightning grounding system.
I'd worry more about a decent ground at where ever the feedline comes
into your house so that you can hook your antenna discharge
unit/transient clamp there.
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