Topband: Beverage Query...

[Ford Peterson]

I'm building my first Bi-Directional Beverage.  It's 9' off the loamy soil and 510' between end posts.  #14 copper house wire spaced 10" apart.  I placed two 8' ground rods at each end (total 4).  One rod is right at the feedpoint, and one 10' away.  The termination end is similarly configured.

ON4UN's book seems to indicate in Tables 7-9 and 7-10 that the two wires configured in this manner should be about 688 ohms.  I checked them.  They are in that 680 ohm area.  But table 7-10 seems to indicate that the impedance of the wires over ground should come in at 340-350 ohms.  In checking this, I placed the termination resistor between one wire and ground.  I find that at about 450 ohms, the lines are pretty flat.  Using my Autek VA1, I changed the impedance of the meter to 450 ohms and find that it is in-fact very good--roughly 1.12:1 on 160M and slowly climbs to 1.5:1 at about 8MHz.

I'm not certain whether John was using empirical or theoretical measurements when he came up with Table 7-10.  And I'm not certain that I understand how to interpret my measurements since they differ by about 100 ohms.  Am I witnessing something attributable to my ground?  Are these wide variations typical of beverages?  Or is John reporting measurements that would be typical of a more average soil?

Any help would be appreciated.

Ford-N0FP
ford at cmgate.com