Sometimes it's just fun to see how far...
http://home.comcast.net/~buck0/outpvccm.html
This link brings you to a collection of e-mail exchanges outlining the
construction of a collinear 5/8th-wave 2-meter vertical. Insights,
discussions and inovations on 2, 3, and 4 stacked elements. Several great
images too.

Special thanks to Paul Anderson N8CVW /7. He took some ideas I played
around with (and posted on the WWWeb over 6 years ago) and really went
hog-wild!!
http://home.comcast.net/~buck0/5-8thx2j.htm

Hope you'll see there is still some fun to be had in the hobby, in the ways
of antenna modeling!

73
Steve KB1DIG

On Sun, 20 Feb 2005 16:15:44 -0500, "Kim & Steve Merrill"
wrote:

Special thanks to Paul Anderson N8CVW /7. He took some ideas I played
around with (and posted on the WWWeb over 6 years ago) and really went
hog-wild!!
http://home.comcast.net/~buck0/5-8thx2j.htm

I wonder what his 6dB gain reference is?

Danny, K6MHE

Danny, K6MHE wrote:
"I wonder what his 6 dB gain is"

There is a "Super J" antenna on page 16-27 of the 19th edition of the
"ARRL Antenna Book". The book says the two stacked 1/2-wave collinear
elements provide about 6 dB gain over a 1/4-wave whip antenna and about
3 dB gain over a 5/8-wave antenna.

I won`t speculate that you actually get more gain from (2) stacked
5/8-wave sections, but it`s possible. Maybe 3 dB more, like a single
5/8-wave over a single 1/4-wave.

6 dB over a 1/4-wave whip is 8.14 dBi.
The 1/4-wave whip has a gain of 2.14 dBi

Best regards, Richard Harrison, KB5WZI

6 dB over a 1/4-wave whip is 8.14 dBi.
The 1/4-wave whip has a gain of 2.14 dBi .......


The half wave vertical should have that 2.14 dbi gain.
A 1/4 wave ground plane should show about .3 db less...
Or when modeled anyway....

In general, a properly designed dual 5/8 collinear should
have appx 5.1 dbi gain. Or appx 3 dbd.... And yes, that
is slightly more than the dual 1/2 collinear should do.
If a single half wave shows 2.15 dbi, I wonder how adding
a second element can add another 3.85 db gain...???
Myself, I think their gain numbers are a little happy...
Also, in that super J article, the 1/4 wave and 5/8's they
compare to are mobile whips...This would greatly skew any
comparisons with the super J, being it's not a mobile antenna.
IE: make it look better than it really is...
An average elevated 1/4 GP will show appx
1.8 dbi or so...Only about .3 db difference from a 1/2 wave
that is elevated.
Of course, in the real world, the results can vary greatly
due to decoupling, or the lack of, etc...
I'd have to check/model the gain of the super J, but I'm
almost sure it would be less than 5.1 dbi...I'll take a wild
guess and say maybe .6 db less??? MK

wrote:
6 dB over a 1/4-wave whip is 8.14 dBi.
The 1/4-wave whip has a gain of 2.14 dBi .......


The half wave vertical should have that 2.14 dbi gain.
A 1/4 wave ground plane should show about .3 db less...
Or when modeled anyway....
. . .

What modeling program are you using that gives those results? A half
wave vertical over perfect ground has about 5.15 dBi gain at the
horizon. The gain when mounted over real ground has zero dBi gain at the
horizon, and much less than 5.15 dBi at any elevation angle above that,
with the value depending on the qualit of ground.

. . .

If a single half wave shows 2.15 dbi, I wonder how adding
a second element can add another 3.85 db gain...???
. . .

A two element array can have more or less than 3 dB gain relative to a
single element by means of mutual coupling. The theoretical limit is 6
dB, which would require impossibly low loss and narrow bandwidth, but 4
or 5 is readily achievable in practice. An increase of much over 3 dB
does require attention to losses and nearly always results in a pretty
narrowbanded antenna. In general, the mutual coupling between collinear
elements doesn't favor high gain, and most collinears have gain increase
of less than 3 dB for a second element. You can learn more about this
topic in Chapter 8 of the _ARRL Antenna Book_.

Roy Lewallen, W7EL

I was using elnec in that example. But I was using "free space".
I was trying to leave the ground out of it...
Also those models were all elevated at 40 ft at the base.
At that height using real ground/average, it had about 3.8 dbi
at 8 degrees.
In comparison, the 1/4 GP with sloping radials did about 1.8 dbi
free space. Real ground at 40ft, was about 3.0 dbi at 9 degrees.
So about .8 db difference using real ground.

The main reason I was sort of skeptical about the 3.85 db
increase was due to your next to the last statement.
I didn't think the close spacing would give that much gain.
As I quick test, I just tried adding another element above
the original, in that model. I used 2 sources to feed.
With the very close spacing of the two elements, the free
space gain was 3.59 dbi...A tad less than I expected...
The real ground numbers were 5.53 dbi, at 7 degrees.
So almost a perfect 2 db increase in that model over
real ground. As a comparison, with about a 1/2 wave
spacing, I got 7.23 dbi using the same real ground.
About 3.4 db increase...Could probably get more
with a wider spacing...
It's this spacing thing that made me dubious...
I couldn't see 3.85 extra, being the elements were
very close using the stub.

BTW...all the models I had were for 10m, at 40 ft....
MK

Roy Lewallen wrote:

What modeling program are you using that gives those results? A half
wave vertical over perfect ground has about 5.15 dBi gain at the
horizon. . .

Correction -- a *quarter* wavelength ground-mounted vertical has the
gain I quoted. A half wavelength ground-mounted vertical has a slightly
narrower pattern, resulting in a little more gain over perfect ground.
It's about 6.9 dBi at the horizon.

Roy Lewallen, W7EL