"Owen Duffy" wrote in message
...
Hello Ian,

Ian White GM3SEK wrote in
:

...
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.

Yes, he does make that statement. I focussed on the diagram.

I guess his "WRONG!" means "possibly wrong (see text)".


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.

I received comment on my antenna described at
http://www.vk1od.net/4over4/ as follows: 'It "doesn't" work because you
have inserted a half-wave time delay in the feed to one antenna (in your
case it appears to be the upper antenna) which tilts the beam up or down
a bit (in your antenna, it will tilt upwards)' and in following
discussion it is asserted that although the feed to one antenna is
transposed, it does not correct the additional half wave phase shift of
the longer branch.

Gordon's paper was offered as support for that position.

I think my design is sound, the rationale is set out in the article. I am
a little flattered if it is considered an advanced technique, but it
seems to me fairly elementary.

Actually, since posting the original article, I followed up on Gordon's
reference to the ARRL Antenna Handbook. It has a diagram that shows
pretty much what I did, it is (c) at http://www.vk1od.net/lost/Fig7.png .
(The difference in my case is that the stacking distance was chosen for
optimal pattern by trial and error with an NEC model, and the coax has a
velocity factor around 0.82.)

Owen

Hi Owen

Richard Clark once told me how to combine 4 antennas in an array. He got
me to feed 4 antennas, 50 ohms each with 50 ohm coax with no dividers. I
just fed each antenna with 50 ohm coax. At the point where the 4 coaxes
get combined, I connected two coaxes in series and the other two also in
series. Then parallel them to get back to 50 ohms. The result is two 50
ohm loads in series to make 100 ohms and with the other 100 ohms in
parallel, the combination is a good 50 ohm load. You can see a sketch in
the Feb 2008 QST. It works pretty slick when the antennas are 50 or 70
ohms where it is easy to get the right coax impedance.

Jerry KD6JDJ