Topband: Center fed beverage transformer

[Victor A. Kean, Jr.]

> Anyone have experience doing this?

Do build a center-fed Beverage, one needs to start with a
two-wire Beverage.  The difference is that one places 
reflection transformers at both ends of the Beverage.  At
the center (actually, any arbitrary) feed point, are 2 
feed transformers normally used in the "reverse feed" 
configuration.  That is, each transformer is wound with
an impedance transformation from the 2-wire transmission
line mode impedance to the coax impedance.

I always use #14 wires with 9 inch spacing, which comes
out close to 675 ohms, which is a 9:1 ratio with 75 ohm
coax, which is easily wound using a 3:1 turns ratio.

The other requirement is that the high-impedance side of
the feed transformers have a center tap, and the two center
taps connect together.  The center tap carries the "normal"
(common mode) Beverage current across the transformers so
that the current can be reflected from one end or the other,
and converted to differential mode.

BTW, I generally don't use reflection transformers, since I
have not been able to see any difference in performance.  I
just tie one wire to ground and let the other float.  As
long as there is some reflection, you'll get a signal.  It
may be that particularly short Beverages may require a better
reflection than longer Beverages.

Here is an ASCII picture of a center fed Beverage feed:

--------          --------
        ) ||  || (
wires   )_||__||_(  wires
        ) ||  || (
        ) ||  || (
--------  ||  ||  --------
          ||  ||
--------  ||  ||  --------
coax    ) ||  || (   coax
        ) ||  || (
--------          --------

You may need to adjust your Email reader to render with a
fixed pitch font to see the picture correctly.

I have a total of 6 2-wire, center fed Beverages for 12
coverage directions.  The shortest is about 480 feet and
the longest is about 900 feet.

Victor, K1LT