As Ian says, the new Handbooks have a much better handle on phasing.
Unfortunately, the wording is a bit unclear unless you already understand
what is going on. At least in the sections I have read.
For example, the new text suggests using 1/4 wl lines to feed each antenna
because a 1/4 wl line "insures equal currents". Unfortunately that rule
applies ONLY when each line is sourced from exactly equal voltages at the
source end! Many phasing systems will not have equal voltages throughout
the phasing system, because the phasing system itself has standing waves.
One simple system that does work for any shift from zero up to 150 or so
degrees is bringing equal length cables (they do NOT need to be any certain
length) to a common point, with an inductor feeding one antenna (in the
direction you want to beam) and a capacitor feeding the other (in the null
direction). You simply "fuss" with the values while watching for a deep
null.
You then match into that system with a tuner. The "phase" inductor and
capacitor should have a reactance variable from several hundred ohms down
to near five or ten ohms at the operating frequency.
Anything "sorta works", but if you get the currents and phase correct the
F/B ratio is phenomenal. I get about 45 dB front to null on my four square
on groundwave. Cutting by ear is the best way, unless you design the entire
system properly.
There is very little change in gain with errors, but there is a big change
in F/B ratio.
73 Tom
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