Ed Swiderski, KU4BP wrote:
>Hello all,
>
>I have a question to all concerning the ground stake for a Beverage. Through
>my reading I see some differnet opinions over the type and size of it. Have
>read about using standard 8-foot ground rods, then 4-foot and then 2-foot
>are OK. Also, I have seen that copper pipe of the same varying lengths and
>diameters are OK. What I would like to know is what has seemed to work best
>for you? ......
>
>
Ground rod impedance varies a lot depending on your soil. In Florida I
used 4 ft ground rods for receiving antennas and they measured about 50
to 70 ohms. That was measured at 2 KHz. I don't know what they were at
2 MHz, but I just used that as a figure of merit. When I tried the same
thing in north Alabama, the rods measured 375 ohms. Nearly all that was
due to contact area between the ground rod and the soil. I know that
because the impedance between two of them placed 1 ft apart measured the
same as two of them 40 ft apart.
As far as what effect that has on a Beverage I only know what EZNEC
says, I don't have any reliable experimental data. A poor ground rod on
the termination end should work OK if you reduce the size of the
termination resistor to compensate for it. For a single direction
Beverage, EZNEC says that a poor ground rod on the coax end reduces the
gain some but doesn't have much effect on the pattern. I haven't
looked at a bi-directional Beverage.
For the rod on the coax end, I don't connect my coax shield to it to
avoid common mode pickup problems. I use coupling transformers with
good common mode rejection. A floating coax does create one more
problem, induced currents on the coax due to close lightning strikes.
To solve that, either a low voltage gas tube surge suppressor between
the coax shield and the ground rod, or a separate ground rod for the
coax shield.
Jerry, K4SAV
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