If you were to use aluminum for the verticals rather than wire, what would
the shortening factor be?

Doug


"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

DOUGLAS SNOWDEN wrote:
If you were to use aluminum for the verticals rather than wire, what
would the shortening factor be?


If it is end-fed, as Hasan recommends[*] then the exact height of the
vertical parts wouldn't matter much.

The main difference would be in the high-angle radiation from the
horizontal part. That radiation is roughly canceled, but in a
half-square the cancellation is never complete... which means any
differences would be very hard to hear.

But be aware that the voltage at the bottom of the far end is very high
indeed. This is no place to use a metal ground post and a thin sleeve of
plastic pipe! I've drilled holes through thick PVC support blocks by
voltage-feeding a half-wave vertical, and this open end is worse.


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