Richard Harrison wrote:
The double-page figure is arranged into (8) vertical columns of
radiation patterns. Each column is for a different physical spacing
between the two parallel elements. All of the (5) patterns in a vertical
column have the same physical space between elements.

The only change between patterns in a vertical column is the phase angle
between the two elements.

Are they assuming equal currents into each element? That's the real trick.
--
73, Cecil http://www.qsl.net/w5dxp



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----

Cecil, W5DXP wrote:
"Are they assuming equal currents into each element? That`s the real
trick."

The subscript says:
"The two elements are assumed to be thin and self-resonant, with
equal-amplitude currents flowing at the feed-point."

If everything is symmetrical, the self-impedances and the mutual
impedances of the two elements should be equal, producing equal powers
into each element.

Roy Lewallen may have been the source of a caution on phasing errors
which appears on page 8-13 of the 19th edition of the ARRL Antenna Book.
Roy is named on page 8-12.

Kraus says on page 284 of the 1950 edition of "Antennas":
"It is important that the antenna power W be considered
constant.---Until the antenna power was considered constant by G.H.
Brown (Proc. I.R.E., January 1937) the advantages of closely spaced
elements were not apparent. Prior to this time the antenna current had
usually been considered constant."

Kraus took a G.H. Brown idea and ran with it producing the W8JK antenna.
He had a lot of trouble gettinng the W8JK antenna story published due to
naysayers. But it works despite its low impedance.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:
If everything is symmetrical, the self-impedances and the mutual
impedances of the two elements should be equal, producing equal powers
into each element.

Unfortunately, it is not that easy except under special circumstances.
The element with leading phase often has a different feedpoint impedance
than the element with lagging phase. For instance:

Given two 1/4WL monopoles, 1/4WL apart, and fed 90 degrees apart with
one amp each will exhibit a gain of 3 dBi in one direction. However,
the feedpoint of one element is 20-j20 and the feedpoint of the other
element is 50+j20. The feedpoint voltages are obviously not equal so
to equalize the current magnitudes takes some juggling. That' what
Roy's BASIC program does - finds a solution if one exists.

I once had a BASIC program that calculated the mutual impedances given
the feedpoint impedance of one element alone and the feedpoint impedances
of the two elements during operation but I seem to have misplaced it.
--
73, Cecil http://www.qsl.net/w5dxp



-----= Posted via Newsfeeds.Com, Uncensored Usenet News =-----
http://www.newsfeeds.com - The #1 Newsgroup Service in the World!
-----== Over 100,000 Newsgroups - 19 Different Servers! =-----