wrote:

Tom, where is the link that goes with this info? It doesn't mean anything as
it stands
Art


What? Of course it means something. It's an equation along with the
constraints.

Run any current decent 1 wavelength, or longer, yagi in your favorite
modeling program, and it will tell you whether you are near the gain you
should get for a well behaved yagi. Or it might tell you the model
isn't very accurate. It works well to test known designs against
unknown quality programs without having the known good modeling program
or test range.

If you want the database it was derived from, that might be arranged,
but it is in from a database program that Microsoft Office won't read,
so you might be out of luck there.

tom
K0TAR

Tom, let me be direct without being disrespectful What I modelled was a boom
length of 7ft for 20 metres and it is an abnormal yagi design which does not
fit what you are offering. I do not believe that NEC programs vary too much
on standard forms but when using tightly clustered elements on a short boom
lots of other things come in to play, and one has to be sure that the
program is all encompassing as designed to handle ALL abnormalities.
Obviously what you have offerred has serious problems on short yagi's let
alone abnormal design yagi's. It is my belief that because an element
reradiates
a portion of the RF that it received, extra elements that are closely
clustered can provide increased gain. Yes. my model
confirmed that but I was hoping that experts could point to a mathematical
analysis of max gain per unit length that was exacting in gain provided and
not "close enough" and not marred by other things that can occur by
measuring in the field.
It would appear from the responses that efforts in this area has not been
undertaken and which I will have to live with that.
But I do thank you for your offering
Art

"Tom Ring" wrote in message
. ..
wrote:

Tom, where is the link that goes with this info? It doesn't mean
anything as
it stands
Art


What? Of course it means something. It's an equation along with the
constraints.

Run any current decent 1 wavelength, or longer, yagi in your favorite
modeling program, and it will tell you whether you are near the gain you
should get for a well behaved yagi. Or it might tell you the model
isn't very accurate. It works well to test known designs against
unknown quality programs without having the known good modeling program
or test range.

If you want the database it was derived from, that might be arranged,
but it is in from a database program that Microsoft Office won't read,
so you might be out of luck there.

tom
K0TAR

wrote:

It would appear from the responses that efforts in this area has not been
undertaken and which I will have to live with that.
But I do thank you for your offering
Art

Sorry, based upon the variability of responses in the group, I thought
this was well within the limits. It was considerably closer to being on
subject than some that have gone from legitimate questions to raving
political nonsense with no one complaining. I won't make this mistake
again.

tom
K0TAR

" wrote in message
news:wAYdd.406148$mD.70164@attbi_s02...
Tom, where is the link that goes with this info? It doesn't mean anything
as
it stands
Art


wrote in message
. ..
wrote:

My ARRL books go back a decade or more
and the graph showing gain per boom length
has several curves based on different measurements
e.t.c. Has a graph been made based solely on NEC
program findings over say a perfect ground and at a uniform height?
Art



For VHF/UHF yagis in free space -

WA2PHW Gain Figure of Merit

G = 10 log (5.4075 B + 4.25) for B GT 1

Where G is gain in dBd and B is boomlength in wavelengths.

This is from a database of over 100 VHF/UHF yagis compiled in the early
90's. These are all real buildable yagis, and the antenna range numbers
closely agree with the computer models. The numbers were heavily
influenced by the 10 to 40 element K1FO series. Thanks again Steve.

Note that this predicts a zero length yagi should have about 6 dBd gain.
Any ideas on why it intercepts there?

tom
K0TAR

Art Unwin wrote:
"My ARRL books go back a decade or more and the graphs showing the gain
per boom length has several curves based on different measurements
e.t.c."

I haven`t encountered similar curves based on NEC, but I`ve found thye
old ARRL curves on page 163 of my 1970 edition of the "A.R.R.L. Antenna
Book" (cover price=$2.50).

Variation between curves from 3 different groups of observers are within
"1 S-unit" (6 dB). Gain ranges from a minimum of about 7 dB for a Yagi
with a 1/2-wave boom length (pessimistic) to a 19 dB gain for a
6.5-wavelength boom length (optimistic).

The optimistic curve is labeled "Greenblum", and seems too good to be
true. The other two curves have flattened out as the number of
wavelengths increases. The Greenblum curve is almost a straight line. As
Kraus showed in his solution to the Deutsche Welle antenna gain problem,
you often need to double the total number of elements to get a 3 dB
antenna gain.

Best regards, Richard Harrison, KB5WZI

Richard, the more I study the boom length question the more I feel that the
ARRL
should drop the three curve gain/boom length graph. First there has to be a
condition that all elements are on the same plane. The other condition must
be
that all the elements are straight and parallel. The more I study the two
element
antenna I find that changing the added element height relative to one
another ,
even if a small distance , can change the gain.
I understand that there are "Landorfer ?"curved elements that can also
increase the gain.
I also proved that by NEC.
If one allows elements numbers to be added to increase ad hoc then NEC shows
that a quasi dish shape will occur
where the focus can stay equal to .1 wavelength and where gain increases to
over 14 dbi.
If one takes a further step by "shaping "the elements whether it be the feed
element or the
reflective elements then not only does the beam width narrow with increased
gain but the
TAO decreases about one degree which is a huge advantage when using small
garden type antennas.
Based on the above findings it would be impossible to generate a NEC curve
that would make sense
unless the above two conditions are set in place for the average amateur.
The latter would give
some protection against fraudulent vendors and supply a datum curve that is
meaningful to all.
I do believe that this posting should put an end to this thread and I thank
you again for your input.
Regards
Art



"Richard Harrison" wrote in message
...
Art Unwin wrote:
"My ARRL books go back a decade or more and the graphs showing the gain
per boom length has several curves based on different measurements
e.t.c."

I haven`t encountered similar curves based on NEC, but I`ve found thye
old ARRL curves on page 163 of my 1970 edition of the "A.R.R.L. Antenna
Book" (cover price=$2.50).

Variation between curves from 3 different groups of observers are within
"1 S-unit" (6 dB). Gain ranges from a minimum of about 7 dB for a Yagi
with a 1/2-wave boom length (pessimistic) to a 19 dB gain for a
6.5-wavelength boom length (optimistic).

The optimistic curve is labeled "Greenblum", and seems too good to be
true. The other two curves have flattened out as the number of
wavelengths increases. The Greenblum curve is almost a straight line. As
Kraus showed in his solution to the Deutsche Welle antenna gain problem,
you often need to double the total number of elements to get a 3 dB
antenna gain.

Best regards, Richard Harrison, KB5WZI

Art Unwin wrote:
"I do believe that this posting should put an end to this thread and I
thank you again for your input."

All the questions answered? Any topic is eventually tiresome, but not
everyone tires of it at the same time. Gain per unit length is likely
not a straight line at any particular frequency. There is probably much
more to be said about best coupling for maximum gain.

There was an article by Joe Reisert, W1JR in the December 1986 issue of
"Ham Radio" about a 28-element, 21-foot boom, 432 MHz (about 70 cm WL)
Yagi Joe built. The gain was about 19 dBi, or about 0.9 dB per foot at
432 MHz.

The pattern shown and gain are said to come from MININEC.

Best regards, Richard Harrison, KB5WZI

Richard Harrison wrote:


There was an article by Joe Reisert, W1JR in the December 1986 issue of
"Ham Radio" about a 28-element, 21-foot boom, 432 MHz (about 70 cm WL)
Yagi Joe built. The gain was about 19 dBi, or about 0.9 dB per foot at
432 MHz.

The pattern shown and gain are said to come from MININEC.

Best regards, Richard Harrison, KB5WZI


That was a 24 foot (7.3 wavelength) antenna, with 19.15 dBi claimed,
which was actually higher than newer modeling programs give it.

tom
K0TAR

Richard Harrison wrote:


There was an article by Joe Reisert, W1JR in the December 1986 issue of
"Ham Radio" about a 28-element, 21-foot boom, 432 MHz (about 70 cm WL)
Yagi Joe built. The gain was about 19 dBi, or about 0.9 dB per foot at
432 MHz.

The pattern shown and gain are said to come from MININEC.

Best regards, Richard Harrison, KB5WZI


Oops, my mistake, 10.5 wavelengths, and about .9 dB under what it could
be, assuming the model is correct for mininec.

tom
K0TAR

There is probably much
more to be said about best coupling for maximum gain.

Maximum Gain, that seems to be all people think about.

Max. Gain is not always a good thing.

Example which is better for 2 meter mobile a 1/4 wave 0 dB whip a 3 dB 5/8
wave or a 6 dB collinear ?

A true 6 dB collinear makes a very poor mobile antenna.
Unless your parked on level ground, then it works fine.

The 3 dB 5/8 wave works good if you are on fairly flat terrain.
But get into the mountains or use repeaters that are on
10,000 ft. + mountains like we have here in WY and Colorado.
A 0 dB 1/4 wave whip can some times work better.

People put a 3 dB gain mag mount on the back corner of the
finder, setting at a 30 degree angle and wonder why it don't work as well as my
0 dB 1/4 wave mounted in the center of the roof of a van. (Mounted in a hole
in the roof, not a mag mount.)

All I am saying is there is more to an antenna than Max gain.
What about bandwidth, pattern etc.

There, I feel better.

73 Al Lowe N0IMW
Arrow Antenna