Ford:
I'm not sure I understand your test setup - did you have the push-pull and
single ended transformers in place while you did the measurements? If so,
the "termination resistor" you added is a spurious element; the push-pull
transformer should match the 688 Ohms impedance between the two wires and
the single ended transformer should match the 350 Ohms to ground. No further
termination is needed.
If you had the transformers disconnected and were measuring just one wire
the 450 Ohms you measured would be the transmission line impedance to
ground, and 450 is a very reasonable value for that.
Chuck
----- Original Message -----
From: "Ford Peterson" <ford@cmgate.com>
To: <topband@contesting.com>
Sent: Sunday, August 15, 2004 7:53 PM
Subject: Topband: Beverage Query...
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@cmgate.com
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