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Author Topic: home-brew sigma 4 11 meter antenna  (Read 64510 times)
BOOTYMONSTER
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Posts: 73




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« on: June 19, 2011, 07:14:39 PM »

tried my hand at making a sigma v . sirio currently makes their vector 4000 which is their version of that type of antenna , but i continuously read comments on forums about the 4000 not be durable in bad weather areas . we dont get nor'easters or more than a foot or so of snow in my area , but we do get hurricanes and pretty high winds at times . so i decided to roll the dice and make one that i think will be sturdy enough . my initial ideas for construction didn't work as well as i though they would so i had to re think and buy new material to make into the parts i wanted . it took a while , but i got it done . here's a link to the entire thread for anyone that may be interested in seeing how it progressed for me as well as my mistakes i made along the way .

http://www.worldwidedx.com/home-brew-mods/102961-booty-4-a.html

im just gonna post pics here of what i ended up with . im starting with a 29 ft vertical length , 108 inch basket element length and a 30 inch loop . the gamma is 3/8 solid aluminum rod and 1/2 inch inside diameter aluminum tubing . i used a simple mobile stud for the coax/gamma connection .

here's the bottom bracket .....




here's the loop with tabs for the basket elements and the basket elements .




putting basket elements on the bottom bracket .



my gamma strap .



a pic of the basket .





and the finished (for now) antenna .





not me in the pic , just one of my buds .

put my astatic 700 meter on it real quick and got a quick and dirty 1.6 or 35 and did a quick check with 2 locals . just sitting literally on the ground it made a good contact with a guy in the city that my other 5/8's (29 ft. to the tip) just barely made through the static . even though its much taller , its a whole heck of a lot lighter than my 5/8s with the big plate and mounting boards
« Last Edit: June 19, 2011, 09:25:29 PM by BOOTYMONSTER » Logged
BOOTYMONSTER
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Posts: 73




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« Reply #1 on: June 19, 2011, 09:27:55 PM »

i guess pics are not allowed here .
all the pics are posted in the thread of the link after the first paragraph .
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N0YXB
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Posts: 303




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« Reply #2 on: June 20, 2011, 08:40:39 AM »

Um, who cares?  I'm sure there's a place for poorly written CB articles out there, but this is not it.

Vince
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Vince
BOOTYMONSTER
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Posts: 73




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« Reply #3 on: June 20, 2011, 12:45:45 PM »

LOL , i didn't build it to make you happy .
got any articles about antennas you have built to share ?
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N0SYA
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Posts: 321




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« Reply #4 on: June 21, 2011, 12:15:22 PM »

Breaker!
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If you have a clumsy child, you make them wear a helmet. If you have death prone children, you keep a few clones of them in your lab.
WB6BYU
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Posts: 13029




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« Reply #5 on: June 21, 2011, 01:03:17 PM »

I have to laugh and shake my head when I see the "magical" properties assigned to some half wave
antennas, and the myths and folklore associated with them.  It doesn't matter what feed system you
use - a half wave antenna can't be any better than a common dipole.  If the difference among any
such antennas (including a quarter wave ground plane, 5/8 wave, J-pole, A99, or the antenna
described here) is measurable, then it is most likely due to high losses in the materials or common
mode current flowing on the coax or mast that distorts the pattern:  you can make such antennas
WORSE than a standard dipole if they aren't built right, but you can't make them perform any BETTER
than one, regardless of the materials and work you put into it.

So if CBers really do measure that much difference between the various sorts of half wave
radiators, that must mean that most are poorly built or installed.

A wire ground plane (quarter wave radiator, with two or more quarter wave radials) hanging from
a tree branch will work just as well - within the accuracy that anyone can measure with an S meter -
as any other antenna with a 1/2 or 5/8 wave radiator when the tops are at the same height above
ground when the feedlines are properly decoupled (which isn't always an easy thing to do.)


Not that I don't appreciate the mechanical engineering that goes into building such an antenna, but
sometimes you have to go back to the underlying theory and consider what you are trying to
accomplish.  Perhaps the objective is to have an impressive looking antenna - this one should work
well in that category.  On the other hand, if the objective is to maximize the microvolts per meter
at a distant station, there may be cheaper and easier methods to achieve the same result.

But both CB and ham radio are hobbies, and there is nothing wrong with building things for the
fun of it.  I don't claim that all my homebuilt antennas are optimum or practical.  But then I'm the
sort of person who will stick a few floppy wires through a piece of wood to make a yagi that
works better than my fancier ones.  We each choose the parts of the hobby that interest us.
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AD6KA
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Posts: 2232




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« Reply #6 on: June 21, 2011, 02:17:25 PM »

Quote
a half wave antenna can't be any better than a common dipole.  If the difference among any
such antennas (including a quarter wave ground plane, 5/8 wave, J-pole, A99, or the antenna
described here) is measurable, then it is most likely due to high losses in the materials or common
mode current flowing on the coax or mast that distorts the pattern:

Well said, especially about the distorted pattern, which also
includes the take-off angle. Here W8JI models 1/2w and 5/8w
antennas compared to a dipole.

http://www.w8ji.com/end-fed_vertical.htm#IMAX

"This is a NEGATIVE gain antenna at low angles.
This pattern is over real earth, where a conventional dipole has about 8 to 8.5 dBi gain.
This antenna about -2 dBd gain maximum.

It has negative gain over a dipole.
The gain over a dipole at most useful angles for DX is about -10 dB
....significant negative gain.
"

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BOOTYMONSTER
Member

Posts: 73




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« Reply #7 on: June 21, 2011, 06:45:01 PM »

thanks for the comments . nice to have something other than a flaming remark that had no bearing on the topic  Grin

this is neither a dipole or a half wave . ive built a dipole , a 1/4 wgp and a few different 5/8 wgp antennas . this will wind up being about a .82ish wl antenna . ground wave or LOS contacts is important to us chicken banders , but we certainly enjoy the DX contacts too . IMO the 1.5ish db gain a 5/8 has over a dipole is trivial , but where the lobes on a antenna put the signal on the horizon makes a great deal of difference . this antenna is essentially a scaled up to an 11 meter version of the Dominator antenna .

http://lpfmantenna.com/dominator.html

my experience tells me there definitely differences between 1/4 wgp's and 5/8 wgp's . where the antenna puts the dominate lobes will dictate how effective it is . as close to parallel to the horizon works best for me and thats my purpose in making this antenna . BTW i do use a air core coax choke on my antennas at the feed point when i put them up to prevent CMC's . 5 loops on a 4 1/4 inch former .

i also think the imax is a poor antenna design that is very well known for bleeding and splattering across multiple channels . i experimented with shorter than 1/4 wavelength ground elements on my 5/8 adventures and im a firm believer that any elevated antenna should have 1/4 wave length ground elements ..... longer than 1/4wl may be better or worse , but i didn't go longer than 1/4 wl on mine . no ground elements is a definite no-no IMO , but we all know what opinions can be like Smiley Smiley

thanks again for being on topic with your comments Wink
« Last Edit: June 21, 2011, 07:12:04 PM by BOOTYMONSTER » Logged
KE6LYU
Member

Posts: 2




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« Reply #8 on: June 21, 2011, 07:45:53 PM »

I was over there reading and they have some interesting antenna threads going, good thread about the Gain Master antenna made by a company in Italy.
Looks like it would work 10 and 12 meters well....
Thank`s for the Link Guy
And Kudo`s to you for building your own antennas, I enjoy seeing guys roll there own as opposed to just buying....you learn more that way.
Do you have your Lic?
If not you should give it a try, we can always use new blood in the hobby, and especially guys that like to home brew.
« Last Edit: June 21, 2011, 07:47:35 PM by KE6LYU » Logged
WB6BYU
Member

Posts: 13029




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« Reply #9 on: June 21, 2011, 10:29:47 PM »

Quote from: BOOTYMONSTER

...this is neither a dipole or a half wave . ive built a dipole , a 1/4 wgp and a few different 5/8 wgp antennas . this will wind up being about a .82ish wl antenna . ground wave or LOS contacts is important to us chicken banders , but we certainly enjoy the DX contacts too . IMO the 1.5ish db gain a 5/8 has over a dipole is trivial , but where the lobes on a antenna put the signal on the horizon makes a great deal of difference . this antenna is essentially a scaled up to an 11 meter version of the Dominator antenna .

http://lpfmantenna.com/dominator.html
...


Well, as colorful as their computer simulation looks, it doesn't support their claim of 3dB over a half wave
antenna.  Even accepting their simulation as accurate, the radiation from the cone is much less than
that from the main radiator itself.  The only way you can flatten the radiation pattern is to lengthen
the antenna to get colinear gain.  A center-fed full wavelength (two half waves in phase) has about
2dB gain over a dipole when the currents are balanced in the two sections.  This antenna is shorter
and the currents are not balanced, so the gain will be less than that.  Might it have one dB gain
over a dipole?  I'm doubtful, but would be willing to listen to a technically competent explanation.
But once an antenna claims more than the laws of physics can provide, I don't believe any of
their performance claims.  (I'm still experimenting with the antenna model, but so far it shows 0.4dB
gain over a dipole, but the vast majority of the radiation is from the upper half wavelength, so
characterizing it as a half wave antenna is reasonably accuracy even though the physical length
is longer than that.)

How important is even 1dB?  I might be able to see the difference on the S-meter of a VHF-FM
radio, as they often have bargraph meters with a range of 10 to 12dB (for perhaps 8 bars.)
A standard meter for SSB can't be read to such precision unless you stick a digital voltmeter
across it and average the responses over time on a steady carrier.  I do have receivers that
will indicate a change of less than 1/4 dB that I use for direction-finding when I need to aim
an antenna very precisely, but such equipment is pretty rare in the ham community.  What I
find on VHF is that 1dB might be the difference between 40% copy and 60% copy in a marginal
environment, but otherwise it makes no practical difference and can't be detected by the
typical operator except in certain conditions.


If you read my comments carefully you'll see that I was comparing antennas with the same TOP
height, not base height.  The only reason that a 5/8 wave antenna has an advantage over a
1/4 ground plane with sloping radials is if the bases of the antennas are at the same elevation,
in which case the point of maximum radiation of the 5/8 wave antenna is higher above the ground.

To get an honest 3dB gain over a dipole would require a colinear antenna stack about 100' high, and
you'd need to mount the base of it at about the same height to see the gain in practice.  If you
built such an antenna with the base near ground level you'd find that the half wave radiator
with the same top height would do nearly as well, because the AVERAGE height of the antenna
is then closer to 100' rather than 50'.

At VHF (and most local communications on CB have more in common with VHF propagation than
some of the lower HF bands) height is more important than anything else for antenna performance.
(Well, other than making sure you don't have a short or open in your feedline.)  Even standing
20' away from a transmitter I can measure the difference in signal strength between holding
an antenna waist high, shoulder high, or over my head.  That's why I use the half wave dipole
at the same top height as my gain reference because it differentiates the gain due to the
antenna design from that due to height above ground.


Anyway, good luck with your experiments!

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BOOTYMONSTER
Member

Posts: 73




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« Reply #10 on: June 22, 2011, 07:40:15 AM »

"If you read my comments carefully you'll see that I was comparing antennas with the same TOP
height, not base height.  The only reason that a 5/8 wave antenna has an advantage over a
1/4 ground plane with sloping radials is if the bases of the antennas are at the same elevation,
in which case the point of maximum radiation of the 5/8 wave antenna is higher above the ground."

thank you sir for clarifying your comment that i didn't give the proper attention too . a very helpful gentleman named Marconi over at WWDX has posted lots of charts from his experiments over the years and typically sees little difference between antennas with their tips at the same height . my results from comparing a 1/4wgp and a 5/8wgp were with the feedpoint within 2 feet of each other . a 30 ft mast is as high as i could possibly go here because it would need to be guyed beyond that . im a renter and the home owner has said running guy wires across the house and yard is a no-no . so for my circumstances the taller antenna at the same feedpoint is my most effective option , as far as an omni antenna goes . no doubt a beam antenna would do better . i do hope to build a 3 or 4 element beam at some point , but that will be quite a bit down the road .

thanks again for your helplful and kind comments .
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WB6BYU
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Posts: 13029




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« Reply #11 on: June 22, 2011, 08:16:18 AM »

The same antenna theory applies for ham, CB, or anything else.  (Unlike some antenna manufacturers
who list radically different gains for the same antenna in each service.)  And understanding the
principles is a good foundation from which to experiment.
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W5LZ
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Posts: 477




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« Reply #12 on: June 22, 2011, 02:46:51 PM »

WB6BYU,
I have to disagree with your comments in Reply #5.  You may not think, or may not have found there to be any legitimate differences between the various 'sizes' of antennas, but there are quite a few of us who have seen those so called 'magical' differences.  That wasn't only on 11 meters by any means.  I do agree that the 'gain' figures cited by some antenna manufacturers have to have originated in the advertising department.  I don't happen to have an antenna range in my back yard so the comparisons I've seen personally are not exactly 'scientific' enough for some.  But that's okay, I quite frankly don't care much, I know there are differences in gain between the 1/4 wave, 1/2 wave, 5/8 wave, etc.  I'm sure the "Jolly Indian" is more often right than wrong, but he would be the first to tell you he isn't infallible.
As for starting in CB radio, I figure there are a lot of us who did.  If you really want to be accurate with it, I started in commercial radio, then CB radio then ham radio.  And opinions about that 'starting' are only worth what you make them worth.  Another one of those "I just don't care" thingys.
 - 'Doc / Paul / W5LZ

... and once upon a time in 1966, WN5LZK.  Wanted that one back but 'they' didn't think I could remember all those letter so gave me this one.  Who knows, 'they' may have been right.
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WB6BYU
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Posts: 13029




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« Reply #13 on: June 23, 2011, 09:08:16 AM »

Quote from: W5LZ
WB6BYU,
I have to disagree with your comments in Reply #5.  You may not think, or may not have found there to be any legitimate differences between the various 'sizes' of antennas, but there are quite a few of us who have seen those so called 'magical' differences...


I'm always willing to be corrected with valid technical information - I'm mostly concerned with getting
the correct data presented to readers than I am to defending a particular position.

But if you look at the current distributions on the various antennas they are nearly identical.  For
example, the difference between 1/2 wave and 5/8 wave radiators is a small amount of out-of-phase
current at the base of the 5/8 wave that actually reduces the effective radiation broadside to the
antenna.  Similarly a ground plane with sloping radials turns itself into a half wave dipole as the radials
are sloped further downwards - there isn't any specific point where the performance suddenly shifts.
All of these are, in effect, half wave radiators, along with a J-pole (an end-fed half wave with a quarter
wave matching stub.)  And, while you can make them worse than the theoretical half wave dipole due
to high losses, feedline currents, etc., you can't make them any better.

So electrically they really are basically the same antenna, with some minor differences in feed system
and construction.  That's why I say that none of them can be significantly better than the rest.

However, they can be installed differently, and this is where the observed differences come into play.
If you put the feedpoint of your antenna at ground level and swap out 1/4, 1/2 and 5/8 wave radiators,
you likely WILL see a difference - that is because the point of maximum radiation is at a different
height above ground.  This is why my statements were conditioned with the TOPS of the antennas
being at the same height.  The point of maximum radiation is 1/4 wavelength down from the top,
and this cancels out the effect of the height above ground from the comparison.

This might seem like nitpicking, but it is actually important for understanding the differences
between two antenna options:  without it, an antenna on top of a 10' mast would be different
than the same antenna on top of a 20' mast.  By breaking the behavior into two pieces (the
antenna in free space, and the effects of the height above ground) we can make a much more
realistic assessment of what differences to expect between two antennas.

For example, I've seen claims such as, "I replaced my old dipole with the fancy XYZ antenna and
my signal improved by 20dB."  If the XYZ antenna is equivalent to a dipole, I might still believe
this statement, but I'd attribute the improvement to something other than the difference in
the theoretical performance of the two antennas.  (Mostly likely the coax was lossy or one
side of the old antenna was broken at the feedpoint.)  Or "my new beam antenna is 20dB better
than my dipole" when the beam can't be expected to have more than 5 to 6dB gain.  In that
case most of the difference may be due to the fact that the beam is mounted on a new tower
at 70', while the dipole was laying on the roof of the back porch.

So, yes, if you are comparing different antennas mounted on your porch rail, the 5/8 wave is
probably going to show an improvement over the 1/4 wave ground plane (especially if there isn't
enough ground clearance to slope the radials downwards.)  But if the ground plane were put on
top of a mast so that the top was at the same height as the top of the 5/8 wave radiator, the
difference would be difficult for most hams (or CBers) to detect.

Is this a valid comparison?  It depends on the construction.  If I have a fixed mounting point it
might not be, but often I can construct a ground plane + short mast using the same materials
as a 5/8 wave or J-pole, and with the same overall height.  If I am limited to the maximum
height I can go without needing guy wires, or am hoisting my antenna up using a rope tossed
over a tree branch, then any of them would work about as well. 

This importance of understanding this is to see that, all other things being equal, I can choose the
one that is easiest to construct using the materials at hand without worrying that it might not be
as good as the others.


Again, I'm happy to be corrected if I've said something that is technically incorrect.  But as far as
I know it is consistent with the current distributions on the antennas, and that is what determines
the radiation patterns.
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K9FON
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Posts: 1012




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« Reply #14 on: June 23, 2011, 09:09:10 AM »

Yup a lot of us started out on CB. if it hadnt been for CB i wouldn't have had any interest in ham radio. I enjoy ham radio but i dont like the atitudes a lot of hams have.  
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