Owen Duffy wrote:
Referring firstly to the left hand one:

I suggest that the figure is in error because the scenario is not
ALWAYS wrong.

My contention is that at a single frequency, the phase inversion as a
result of the left to right swap of one driven element (DE) wrt the
other can be fully compensated for by ensuring that low loss feedline
to one DE is an odd number of electrical half waves longer than to the
other.

Where the low loss feedline to one DE is an odd number of electrical
half waves longer than to the other, the Yagis are driven in phase.

The outcome being that the pattern at that frequency is approximately
the same as if equal length feedline branches were used.

Referring now to the right hand one:

I suggest that the figure is in error because the scenario is not
ALWAYS wrong.

My contention is that at a single frequency, that where the low loss
feedline to one DE is an integral number of electrical full waves
longer than to the other, the Yagis are driven in phase.


In fairness, Gordon did say: "Departures from these rules are possible
for special applications outside the scope of this discussion." The
exceptions identified above would be exactly what he had in mind.

Reversed connections and/or unequal feeder lengths certainly can be
used, but they are advanced techniques requiring clear intent and
careful engineering. In all other cases they will be "WRONG" as Gordon
says.


--

73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek