John Smith wrote:

Cecil:
Yes Cecil, there is wisdom in your words...
However, as I pointed out, I am now focusing on "received signal", its'
quality and strength.
After having given it some thought, that is what is most important. In an
grave emergency I have the ability to bring multiple kilowatts on line (yes,
I have the generator to support it.) What I can't do is guarantee that for
the fellow at the other end of the contact. So, I am focusing my attention
towards his/her benefit--in the refinement of my ability to pull
sub-nano-watts from the ether...
EZNEC and all other calculations are great, I appreciate what can get me to
ballpark figures with matching, lengths, spacings, predictions, etc.
But, in the end, the humble s-meter on a known transceiver, compared against
know signals and similar conditions will be my final guide and the
determining factor.

I think you'll eventually end up finding out you just need a big tower
and a big beam.

ac6xg

Roy, W7EL wrote:
"Who cares that you have a 50 dB null in one particular very narrow
direction, if a few degrees away the response is 40 or 50 dB greater."

This is an example of Roy`s earlier post which noted differences between
amateur requirements and commercial requirements. Roy is right. There
are real differences.

Commercial licensees operate on assigned frequencies and enjoy some
protection from interference on their assignments. A broadcaster may as
a condition of his license be required to have a null in one or more
azimuths in his pattern to protect another broadcaster who was there
first. In this broadcaster`s case, he is interested in the narrow null
and may very well expect and hope his signal a few dgrees away is 40 or
50 dB greater.

Best regards, Richard Harrison, KB5WZI

Hmmmm, your analysis is interesting. The gamma looks very much like an
"auto-transformer" to me--the gama-rod like a variable primary, the
secondary being the complete driven element.
I suspected the action would be identical to the auto-transformer--where ALL
the turns in the secondary deliver power to the load....

Regards,
John


--
I would like to point out, I do appreciate the "Been there--done that!"
posts. Indeed, now your observations, comments and discourse should be
filled with wisdom--I am listening!!!
"Cecil Moore" wrote in message
...
Cecil Moore wrote:
I knew I was confused about what you were trying to do.

John, I just realized what is wrong with gamma feeding a
1/2WL vertical at the base. The currents in each side of
the gamma feed section are pretty much out-of-phase so
they don't radiate (much). Conclusion: Gamma feeding a
1/2WL antenna at the base results in a field strength
comparable to a 1/4WL vertical and the minuscule amount
of gain is not worth the effort. Antenna gurus probably
already knew that but it just dawned on my concrete brain.

In much the same way a Zepp or a J-Pole is not a 3/4WL
radiator even though they are 3/4WL long, a gamma match
on a base-fed 1/2WL vertical doesn't yield a 1/2WL
electrical radiator. For this reason, the length of a
gamma match should be considerably less than a wavelength.
A good rule of thumb is probably in the ballpark of less
than ~6% of a wavelength. Your idea seems to require about
16% of a wavelength.

Moral: Physical length and RF electrical length are not
always the same.

What you are trying to do apparently requires a J-Pole
or Zepp approach, i.e. a physical 3/4WL antenna.
--
73, Cecil http://www.qsl.net/w5dxp

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Cecil:

Maybe I sent you the wrong .EZ file.
Anyway, I went back and pondered over your example, DUH!, it was obivious, I
simply had to splilt the driven element into two sections where the gamma
joined it!

Oh well, I might have made myself look stupid today, but not to such a great
extent that I won't be able to top that tomorrow!!!

Regards,
John

--
I would like to point out, I do appreciate the "Been there--done that!"
posts. Indeed, now your observations, comments and discourse should be
filled with wisdom--I am listening!!!
"John Smith" wrote in message
...
Cecil:

Here is an EZNEC file I am having a problem with, it is complaining about
wires 5 and 2 NOT meeting at an end or segment?
What corrects this?

Thanks in advance,
warmest regards,
John


--
I would like to point out, I do appreciate the "Been there--done that!"
posts. Indeed, now your observations, comments and discourse should be
filled with wisdom--I am listening!!!
"Cecil Moore" wrote in message
...
Cecil Moore wrote:
I knew I was confused about what you were trying to do.

John, I just realized what is wrong with gamma feeding a
1/2WL vertical at the base. The currents in each side of
the gamma feed section are pretty much out-of-phase so
they don't radiate (much). Conclusion: Gamma feeding a
1/2WL antenna at the base results in a field strength
comparable to a 1/4WL vertical and the minuscule amount
of gain is not worth the effort. Antenna gurus probably
already knew that but it just dawned on my concrete brain.

In much the same way a Zepp or a J-Pole is not a 3/4WL
radiator even though they are 3/4WL long, a gamma match
on a base-fed 1/2WL vertical doesn't yield a 1/2WL
electrical radiator. For this reason, the length of a
gamma match should be considerably less than a wavelength.
A good rule of thumb is probably in the ballpark of less
than ~6% of a wavelength. Your idea seems to require about
16% of a wavelength.

Moral: Physical length and RF electrical length are not
always the same.

What you are trying to do apparently requires a J-Pole
or Zepp approach, i.e. a physical 3/4WL antenna.
--
73, Cecil http://www.qsl.net/w5dxp

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have you tried this???
http://www.google.com/search?hl=en&q...ch+yagi+design
lots of sources for design info, some software, plenty of pointers.
basically once you have a yagi and decide to feed it with a gamma match you
have the following variables you can work with (assuming you aren't going
to change the diameter of the driven element)...
1. rod diameter
2. rod to driven element spacing
3. location of shorting strap
4. value of capacitance
5. length of driven element(don't forget this, it is very important part of
adjustment!)

now basically you pick a rod diameter, usually 1/3 to 1/2 the diameter of
the driven element, but basically whatever you happen to have handy that is
a reasonable length. then make a few brackets to space it a couple inches
from the driven element, from about 1" on 2m to maybe 4-5" on 20m. so that
fixes 1 and 2.. then you have 3 other variables you can adjust to get the
match you want. if you can't find a good match after systematically running
through the other 3 then try changing the spacing a bit and start again...
but i've always been able to get a decent match by just picking what was
handy for tubing and spacers.

and don't overlook a T match. if you use a 1/2 wave phasing line and the
right diameters and spacing you can get away without a capacitor. this
makes for a fully dc grounded plumbers delight construction that is very
rugged and simple to adjust. this was how all the old telrex monobanders
were fed.



"Jim Kelley" wrote in message
...


John Smith wrote:

Cecil:
Yes Cecil, there is wisdom in your words...
However, as I pointed out, I am now focusing on "received signal", its'
quality and strength.
After having given it some thought, that is what is most important. In
an
grave emergency I have the ability to bring multiple kilowatts on line
(yes,
I have the generator to support it.) What I can't do is guarantee that
for
the fellow at the other end of the contact. So, I am focusing my
attention
towards his/her benefit--in the refinement of my ability to pull
sub-nano-watts from the ether...
EZNEC and all other calculations are great, I appreciate what can get me
to
ballpark figures with matching, lengths, spacings, predictions, etc.
But, in the end, the humble s-meter on a known transceiver, compared
against
know signals and similar conditions will be my final guide and the
determining factor.

I think you'll eventually end up finding out you just need a big tower
and a big beam.

ac6xg

Cecil:

Here is the crux of my fruitless attempts to use EZNEC...
With EZNEC, when I plug in the value of my gamma rod and -jxr, along with
all other elements, EZNEC spits out an error! (something about too short a
loop seems to bother EZNEC, but this short loop IS working!)
However, I am looking at a REAL and functional antenna which appears to be
well matched and receiving well.
So, I end up throwing up my hands and just using the antenna and going about
with the "cut-and-try" method! (probably just my inability to use the app)

Regards,
John
--
I would like to point out, I do appreciate the "Been there--done that!"
posts. Indeed, now your observations, comments and discourse should be
filled with wisdom--I am listening!!!
"John Smith" wrote in message
...
Cecil:

One element I do not understand in EZNEC is: say I end up with 225 ohms
inductive reactance in the gamma rod(just an example figure, use any you
please), how do I inform EZNEC I am inserting a 225 ohm capactive
reactance,
at the feedpoint to offset it?
Or, I am all wet in considering this?

Regards,
John

--
I would like to point out, I do appreciate the "Been there--done that!"
posts. Indeed, now your observations, comments and discourse should be
filled with wisdom--I am listening!!!
"John Smith" wrote in message
...
Cecil:

Your work with EZNEC is greatly appreciated here.
Your configuration is for a horz ant and I am working with a
vertical--conversion is trivial.
"A picture is worth a thousand words..." has real significance here.
I am sure an analysis of your file will provide me with insight into the
workings of EZNEC and accelerate my learning curve!

THANKS!,
John

--
I would like to point out, I do appreciate the "Been there--done that!"
posts. Indeed, now your observations, comments and discourse should be
filled with wisdom--I am listening!!!
"Cecil Moore" wrote in message
...
Cecil Moore wrote:
John Smith wrote:
I cannot find a configuration on the gamma which brings the swr under
that figure...

As Richard H. said, find the point where the feedpoint
resistance is 50 + jXL ohms. That must occur somewhere.
Then tune out the reactance with a series capacitor.

I've used EZNEC to model a gamma-fed 33' 20m dipole at
40' made out of 0.5" aluminum tubing. With a gamma element
three feet long 6" below the 33' element and a series
Xc=122 ohms, it indicates a feedpoint impedance of
49+j0.3 ohms. The EZNEC file can be downloaded by
clicking on the link below.
--
73, Cecil http://www.qsl.net/w5dxp/GAM20DIP.EZ


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John Smith wrote:
"However, I am looking at a REAL and functional antenna which appears to
be well matched and receiving well."

Congratulationns!

In a previous posting, I quoted Dr. Arnold King who wrote prior to 1945:
"The accurate calculation of the (antenna) input impedance at AB of the
modified antenna as a function of the impedance (presented to the
matching section) and the (wire) lengths AC and BD has not been
accomplished."

If it were easy to calculate, they would have done it. They had
excellent marhematicians prior to 1945, too. The implication is that you
find the match by trial. John proved he could do it.

Best regards, Richard Harrison, KB5WZI

John Smith wrote:
Cecil:

One element I do not understand in EZNEC is: say I end up with 225 ohms
inductive reactance in the gamma rod(just an example figure, use any you
please), how do I inform EZNEC I am inserting a 225 ohm capactive reactance,
at the feedpoint to offset it?

Use the "Loads" feature to install a lumped point load of
any Q. For instance, a coil might be 10 + j300 ohms or
a cap might be 2 - j500 ohms. The position of a load
is similar to positioning a source.
--
73, Cecil http://www.qsl.net/w5dxp

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John Smith wrote:

Cecil:

Maybe I sent you the wrong .EZ file.
Anyway, I went back and pondered over your example, DUH!, it was obivious, I
simply had to splilt the driven element into two sections where the gamma
joined it!

Oh well, I might have made myself look stupid today, but not to such a great
extent that I won't be able to top that tomorrow!!!

I dare say all of us EZNEC users have committed that infraction,
some more than once. :-)
--
73, Cecil http://www.qsl.net/w5dxp

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John Smith wrote:

Cecil:

Here is the crux of my fruitless attempts to use EZNEC...
With EZNEC, when I plug in the value of my gamma rod and -jxr, along with
all other elements, EZNEC spits out an error! (something about too short a
loop seems to bother EZNEC, but this short loop IS working!)
However, I am looking at a REAL and functional antenna which appears to be
well matched and receiving well.
So, I end up throwing up my hands and just using the antenna and going about
with the "cut-and-try" method! (probably just my inability to use the app)

Or maybe not. EZNEC apparently won't properly model
the Lattin antenna. www.g3ycc.karoo.net/lattin.htm

Somewhere I have a .ez file that shows 20 dBi omni-
directional gain from an inverted-L antenna. Now that's
what you need. :-)

And you taught me something today. I didn't know one
can attach .ez files to a newsgroup posting.
--
73, Cecil http://www.qsl.net/w5dxp

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