Gene Fuller wrote:
Cecil Moore wrote:
AI4QJ wrote:
... it is plain and simple "intuitive" once you know that current
changes along the electrical "degree length" in an unloaded antenna,
the same should happen in the degree length loaded coil.
Unfortunately, both sides cannot be right but both sides
are still illustrated as fact in the ARRL Antenna Book.
There's one graphic that shows the drop in amplitude
through a loading coil and another that shows no change.
Apparently, the ARRL doesn't know what happens so they
show both possibilities as technically correct.


Every author has a problem in drawing those diagrams, because we are
trying to draw too many things at the same time: physical height,
electrical height, loading coils, current distributions and voltage
distributions. It doesn't matter which viewpoint we are trying to
illustrate, it is still impossible to draw *all* of those things
truthfully to scale on the same diagram.

When comparing the full quarter-wave against the mobile whip, we have to
choose: do we draw the two antennas to true physical scale; or do we
use an 'electrical' scale of 0 to 90deg? Whichever one we choose, the
scale for the other on becomes grossly distorted, and this is what leads
to confusion.

Every author has trouble with this. Illustrations by different authors
attempt to square the circle in different ways, but none of them ever
can succeed because it fundamentally cannot be done.

ARRL publications are no exception, and a further complication is that
the handbook compilations tend to re-use illustrations from individual
articles by different authors. So please don't read too much into the
mixture of drawing styles - the reasons are often more historical than
technical.

Also, as indicated, the pictures do say 1000 words and it also looks
like W8JI ended up agreeing with you after you pointed out the same
effect at "ON4UN's Low Band DXing", 3rd Edition, on page 9-34.
Unfortunately, it is rumored that W8JI has talked ON4UN
into changing that in the latest edition. I emailed ON4UN
about it but got no reply.

It has been changed. There is no longer any discussion of "degrees",
only "current".

Well, not quite. The 4th edition does use degrees for the electrical
lengths of the plain unloaded sections (which is valid from everyone's
point of view); but it no longer implies that the loading coil
"replaces" any number of degrees.

I don't know the detailed history behind that change, but I do know one
thing: ON4UN is not a man to be swayed by "political" influence. The
change in the 4th edition would be because he was challenged to look
again at the *technical* issues, and then he made up his own mind.



--

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