Hi Ian,
I thought you meant something like that, but I couldn't figure out how to
say it, and thought it would be "cute" to make a little joke at your
comments. Then I thought of "if you want to feed it with coax" way to state
what you were saying, but that wouldn't work either, because the tapped coil
is coax fed too. The real issue is how "easy" it is to direct feed with coax
by using the corner feed...but it has a host of common mode issues that
aren't that much easier to deal with than making the coil/cap combo in the
first place. The only thing that maks the corner feed "easy" is doing it
wrong and ignoring the common mode problems with routing of the feedline.
While I did write the article for HR mag, I must admit my only contribution
to the "art" was the clever use of a piece of coax for a high voltage,
easily tuned capacitor. If I hadn't hit on that solution, I would never have
even tried the half-square, as the weather protection and availability of kw
handling caps is a real issue.
I would encourage anyone wanting to do the half-square (a marvelous antenna)
to consider a piece of coil stock and a few inches of coax for the feed
point, in place of the corner feed. (Of course, this requires a VSWR bridge
or Antenna Analyzer to adjust the tap on the coil, but it certainly isn't
rocket science.) I used the 40m half-square for many years and it performed
flawlessly and required zero maintenance in a harsh Iowa climate of wind,
snow and ice.
The method I used for building it couldn't have been simpler. What I did was
get out a long piece of stranded wire, slid two egg insulators on 33 feet,
twisted the first insulator once or twice to anchor the insulator, slid the
2nd insulator 66 feet from the first, twisted it once or twice to anchor the
2nd insulator (now we have both corners), and then measured another 33 feet,
and cut the wire.
The nice part about this is, no soldering at the corners, one continuous
piece of wire and away ya go. I then pounded a ground rod in under the first
corner, mounted the air dux coil/coax cap bottom directly to the rod and the
bottom of the first vertical wire to the top of a plexiglas plate that held
the coil. Just about as simple as one could get. All the strain is on the
plexiglass.
I waterproofed the coax with a blob of clear silicon rubber....caution
here....the antenna will stop working until the blob "cures", as it shorts
out the open end of the coax (I chased this problem for a few hours until I
realized that until cured, the silicon rubber is a short circuit.
This configuration lasted many years and required no attention. I did end up
putting a plastic box over the coil to keep the snow/ice off the coil, but
that's all it took. I've often thought of putting another one up here at the
new qth, but I don't have trees in the right place like I did at the other
qth.
Anywho, my comments were all in good fun. Your observations evoked a lot of
pleasant memories from years ago about an antenna that was instructive and
fun to build, not to mention a sterling performer on 40m.
p.s., yes I did run it on 80m as well, and I was surprised how well it
worked, but then again, it becomes and end fed half-wave "bent" antenna. Two
for the price of one, "sort of".
73,
....hasan, N0AN
"Ian White GM3SEK" wrote in message
...
hasan schiers wrote:
"Ian White GM3SEK" wrote in message
...
Original poster said:
I was thinking
of feeding it at the corner, I think it will be close to 50 ohms.
Ian said:
That's where it must be fed. Anywhere else, and it won't act as a
half-square (except the other top corner of course).
================================================ ====
eh?
Fed at the bottom via a parallel tuned circuit works, no ? You can see my
article in Ham Radio Magazine from many years ago on how to feed it that
way, (which is really the classical feed for this antenna...the corner
fed,
with all of it's inherent problems came along a lot later, AFAIK)
Simply use a parallal tuned circuit at the base of either vertical, and
tap
up from the bottom (ground side) of the coil for 50 ohms. The tuning cap
for
the coil can be a piece of coax (at "x" pf per foot).
Sorry, Hasan, you're absolutely right of course. I remember your Ham Radio
article very well.
What I should have said was "if you intend to use coax feed..."
It's also true that coax feed is not as easy as it looks, because of the
"hot feedline" problem. In many ways a small ground-mounted ATU is
better. Since the half-square is a monoband antenna, the ATU is "set and
forget" and it's very easy to get going as you say.
Well, not quite monoband... with different ATU settings, a 40m half-square
will also work as an end-fed half-wave "inverted U" for short skip on 80m.
I ran this antenna for
years, and I had the mistaken notion that it was a "half-square". Wonders
never cease...I would have thought the editor of the mag, a seemingly
knowledgable fellow, would have caught my mistake.
very big grin, tongue in cheek
Even editors can have a bad day... looks like yesterday was one of them
:-)
--
73 from Ian GM3SEK 'In Practice' columnist for RadCom (RSGB)
http://www.ifwtech.co.uk/g3sek