Topband: Beverage antenna ground

[K4SAV]

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