[Elecraft] ATU efficiency and the Elecraft T1

[Bob Cunnings]

On 8/8/05, Stuart Rohre <rohre at arlut.utexas.edu> wrote:

> This was done for a floating system, or a closed system, ie dipole in space,
> no other ground.  That would pretty well approach the floating system you
> have used on rock.
> 

Well, my thinking went like this:

Imagine I connected a 3/4 wavelength wire to the ant output on the
KX1, and a 3/4 wavelength counterpoise to the rig's chassis (which is
floating with respect to ground). A current maximum would exist at the
2 points of attachment and equal and opposite currents would flow into
the two wires. Now if the first 2/3 of each wire were paralleled to
form a transmission line with the remaining 1/3 arranged to form a
dipole antenna, nothing really changes except that now only the dipole
elements radiate, since the currents on the 2/3 of the wire formed
into a transmission line are (still) equal and opposite in phase. The
system remains balanced with respect to ground, by virtue of the fact
that the chassis is floating. As noted by others, this arrangment does
have a drawback - RF voltage will be present on the chassis. I hadn't
thought about that. Since I'm using resonant dipoles with balanced
feedlines cut to 1/2 wavelength the voltages probably aren't that
high, but upon reflection I can see why the balun would be nice to
have for that reason alone. Oh well, just an oz. or two more weight to
carry if I want to use one.

Thanks all,

Bob NW8L