Sent:
Friday, January 07, 2005 8:04
PM
Subject: comments on stacked 5/8 wave 2-m antenna
Hello Steve, KB1DIG
Just wished to pass along my thanks for
posting this antenna
project on the web. http://hamgate1.sunyerie.edu/races/antenna/5-8thx2j.jpg
I assembled it in a couple hours, tuned and
tested to
a very low VSWR. I used 450-ohm ladder line for the 1/4-wave matching
section.
After tuning for 146 MHz, the matching stub resulted in being
16-inches
long with the feed point 2-inches from the shorted end. This might be a
result of the (2) 5/8-wave sections plus 3/8-wave phasing section being
slightly too long, although I tried to measure carefully (47.5 + 47.5 +
28.5), and the 6-ga wire I used was a little unwieldy, there shouldn't
have been more than 1/4~1/2 inches error. Perhaps there are velocity
effects
from being tie-wrapped to the PVC.
Anyway, it tunes up great. The next step is to
enclose
it in the PVC. I plan to cut upper and lower tubes for the 5/8-wave
sections,
joining them together at the center with a coupling piece notched out
so
that that 3/8-wave phasing section can exit. I also plan a 3/4-inch ID
tube at the bottom to enclose the matching stub.
I will not glue the sections together for now,
so that
the antenna can be folded up for travel and portable use. When I have a
chance to check the gain I'll let you know this too.
Thanks again! Paul Anderson N8CVW
/7
Hi Paul,
Thanks for checking out
this design.
Not sure if you have
seen this Web-page
(for the same design) too.
http://home.comcast.net/~buck0/5-8thx2j.htm
This 5/8th collinear design
has
been very popular. Was even translated into a few different
languages
over the past 5 years. Hard to believe it has been floating
around
on the Web for 5 years...hihi.
Great idea with the
450ohm ladder-line!!
Check this link out.
http://home.comcast.net/~buck0/ll_coolj.html
Ladder-line has become one
of my
(our) new favorite materials for antenna modeling.
Can you send an image of
the final
completed project?
Also, is it okay to post
your comments
(and images) on the antenna? Others will surely benefit from your
observations and modifications.
73
Steven W. Merrill, KB1DIG
buck0@comcast.net
kb1dig@arrl.net
Steve,
Thanks for your reply! Nice to get a
reminder to
take some photos before it becomes just a tube of PVC with a folded
element
dangling out the side.
Will do!
I forgot to mention that instead of the
de-coupling turns
of coax at the base, I placed a couple generic clamp-over noise
suppression
ferrites from Radio Shack at 14-inches below the feed point (~1/4-wave
in RG58 .66 VF). The RG58 is only about 18-inches, just enough for a
short
connection pigtail.
I will also note that the reflected power just
budges
the BIRD wattmeter with a 5-watt element installed, so maybe 100mw,
with
about 5 watts forward. This increases to around 400-500mw at the band
edges.
I should have some photos for you this
weekend. And sure,
feel free to publish my comments.
I know it can be frustrating to build an
antenna that
just can't seem to work. You really wonder if some of these web
projects
ever saw the light of day!! I built a 2-meter 4-element x
1/2-wave
coax collinear that never even got close to tuning up. I can't really
figure
out how it was supposed to work, not having any impedance matching
element.
I plan to play around with adding a 1/4-wave section to see if I can
get
it to tune. If it ever works I'll tell you about it.
I'll be back with the photos...
Thanks again & good evening, 73
Paul Anderson N8CVW /7
Okay
Paul,
Thank
you so much for taking the time out to do the images. This is how
we learn. (And, the best part of the hobby for Kim and I
!!)
Seeing what others come up with. Everyone has a different spin on
things. All great ideas. Stuff we will never think of....;-)
Kim
and I get some really interesting e-mail from our Hampage...
Speaking
of 1/2-wave x4 stacked elements... Paul, you will get a kick out
of this one. Sean, M3FVB submitted this link to his site, with
information
on building a 2m J-Pole 8db Collinear: http://homepage.ntlworld.com/s.amesbury/M3FVB/8db%20collinear.htm
Sean tells me this one works...;-) I have not tried to do
this...;-)
The
1/2-wave 2M J-pole single-element or collinear (2-element) versions
will
work great on both "2M or 70cm". So, this 1/2-wave design is
actually
a dual-band antenna design. (1/2-wave x4 stacked
elements...
70cm...?????????)
I
think the 5/8-wave single-element 2M J-pole will work okay on 6M?
Not sure about the collinear? Something I plan to look into
soon.
Will be great to do field-testing this spring, while the band is
(should
still be mostly) dead quite.
I've
built some crazy stuff that just works, in the past, too...ha ha.. One
of the most interesting was (is) this 2M-Halo or dead-short-halo
design:
http://home.comcast.net/~buck0/2m_halo.htm
It's really only an inside-out upside-down j-pole. Mobile 2M SSB
is getting popular too. This thing costs about $5.00 to
build.
Check out some of the comments: http://home.comcast.net/~buck0/halocom.html
Lots of images from all over.. Several new mods too..
Remember!!
Have fun!!
73,
Steve KB1DIG
Hi Steve
Here are
some photos
of the antenna. As you see, I decided to stack (3) elements. With the
10-ft
support tube it totals about 18-ft. I settled on 3/4-inch PVC for the
two
upper sections, and 1-inch for the lower support tube. The 450-ohm
ladder
line matching stub fits nicely inside of the 1-inch PVC. I used 6-gauge
stranded/insulated wire. There is no internal support (eg, doweling) at
present. We had some 15-mph winds this morning with slightly higher
gusts,
no problem, it just flexes and returns easily. I suspect if winds were
up around 50+, it would probably need some guy lines.
The two
element version
gave nice performance, the extra element might be good for a couple of
extra S-units, some better quieting.
I've been
testing the
two versions by accessing a repeater (W7EI) that's about 66 "GPS" miles
away on Mingus Mountain at about 7000-ft elevation, I'm at about
2300-ft.
here just southeast of Carefree, AZ. Between here and there it is
all mountains. I can sometimes open the repeater with as little as
3-watts
(162.2Hz Tone Coded Squelch), but have had almost full quieting QSOs
with
about 40 watts. Funny, but I cannot open this repeater from my mobile
3.5-dB
Comet 767 whip even with 140 watts.
According
to
http://www.w8ji.com/stacking_broadside_collinear.htm
spacing
makes a huge
difference. My theory is that the stacked 5/8-wave elements are really
just stacked 1/2-waves, but with extra spacing provided by extending
vertically
1/8-wave of the phasing section. This would make the spacing 5/8-wave.
Something I read claimed that the only difference between an end-fed
5/8-wave
vertical and an end-fed half-wave vertical is a lower feed impedance
with
the 5/8-wave. Anyway, being made of wire, this is a convenient and
inexpensive
way to get multiple collinear stacked vertical elements, with spacing.
By the way, the forward/reflected power is 15:1, which is under 1.5:1
SWR,
and I could probably do even better if I started over with a new
matching
stub and retuned. I recommend against making any adjustments on the
length
of the wire. Things got kind of erratic when I tried clipping 1"-1.5"
from
the length of each element. Strangely, the SWR increased in the middle
of the band and lowered at the band edges. I put everything back to
47-1/2
inches for each element.
I think
this design
is pretty good. One thing it has that the "coax collinears" don't have
is some element spacing. By the way, I've tried a couple of different
design
versions on my 4-el. (halfwave) coax collinear, and still cannot get
better
than 3:1 fwd/ref power on the wattmeter, or about 3.5:1 SWR. The last
thing
I could add that I have left out, according to one of the designs, is
the
1/4-wave coaxial sleeve balun. Not too sure I'll go any further with
the
coax collinear.
Let me know
if there
are any other photo shots or discussion that would help.
best 73,
Paul N8CVW
a close-up to show the 3/8 wave phasing elements
the antenna mounted in a tripod with 5-ft. steel
mast.
kind of hard to see the lower phasing element, but it's there.
detail photo to show notching in the pvc coupler
and
tube, makes assembly/disassembly quick and easy for adjustments,
etc
all that's left is to bond the pvc parts together
and
waterproof the openings with caulk
connection of the 1/4-wave matching stub (450 ohm
ladder
line) to the first/bottom antenna element
connection of the coax feedline to the low
impedance
end of the matching stub. final best match was located on the next
connection
point, approx. 5 inches from the shorted end. (exact measurements of
stub
length and tap point to be provided
Hi Paul,
Thank you!!
The images really add a
lot to this.
I should have everything posted in a few days. Will makeup some
smaller
thumb-nail images with the other larger ones attached...all that crazy
web stuff...;-)
I really like the ideas
of the 450
ladder-line matching section and mostly everything but the phasing
stubs
placed inside the PVC. Significant improvements over my
designs.
Should really make a difference when exposed to the elements.
Especially
rain. And, I'm thinking perhaps ~9dbi gain for a 5/8th x3
element.
That's a lot!! Who needs a yagi with gain like that?
I'll let you know when
it's up and
posted too. Will send you a shortcut-link back to the comments
page.
Thank you,
73
Steve KB1DIG
Hi Steve
Comet advertises 8.5dBi for their 3x5/8-wave
"GP-9" (~$200.-
!!). However, being a dual-bander there might be some inefficiency
somewhere,
but that's only a guess, I don't know any more about the design that
would
even suggest that.
Just in case it isn't clear from the photos,
the phasing
elements are not enclosed, the wire that forms them actually exits from
the PVC, loops over for the 28.5 inches, then re-enters the PVC and
continues
on.
Also to note, I do have a dual band log
periodic that
advertises 6dB (i?) on 2 meters, and the stacked 5/8 is doing a
slightly
better job. But to be fair, the top element of the 5/8 is up in the air
higher, but given my location at 2300-ft I'm not too sure that matters
much for most contacts (about 1000-ft above Scottsdale with a gradual
slope,
good line-of-sight).
I'm still dreaming up some improvement over
the PVC that
would be more rigid, it does bend and sway a bit. Maybe even just an
aluminum
tube arrangement like you find for the HF verticals, with the phasing
sections
added in of course. If it ever materializes I'll let you know.
Also, I'll get you a better photo of the whole
mast. The
one I sent is pretty obscured for the lower phasing element, being in
front
of the foliage.
Have a great evening, hope you're not too
snowed under
over there!
Paul N8CVW/7
Hi Paul,
I understand about the
phasing coils
being outside the PVC. What's good is that they are also incased
with the plastic wire covering. Really looks slick!!
Here we run a knock-off
of the Diamond-510
17' vertical 2M-70cm on a 50' tower.
It's the one sold
here: http://www.antennawarehouse.com/Amateur/New_gain_dual_band.htm
They call it the
9/11...
9 on 2M.. 11 on 70cm.. Was just looking at the page a
little
closer tonight and it says: " 8.3 dB better than a 1/4 wave on 2mt.,
11.7
dB better on 70cm" The overall performance of this antenna on
70cm
is not the greatest...strange...70cm is kind-a dead in this area,
anyway..
2M is really great!! Anyhow..we are about 100' above sea level
and
10 miles inland from the coast. 100w with the Kenwood
ts-2000.
We can pull up all kinds of stuff on 2M with this thing...;-) On
2M/FM, If we can hear it, we can work it.
The truth is, I bought
this thing
because I couldn't figure out a way to build one as good as this.
It's been up for 2 years now and withstood up to 75mph wind gusts.
(SNOW...just another 4
letter word)
About 17" of new snowfall here in Dover, NH over the weekend. I
work
in Wakefield, Mass. 60miles to the south, and located just
outside
the city of Boston. They got something like 30" down where I
work.
A real blizzard!! Was snowing sideways with all the wind...ha ha
Be good & Have a
good evening
too!!
Thank you!!
73
Steve
KB1DIG
Ref: "connection of
the coax
feedline to the low impedance end of the matching stub. final best
match
was located on the next connection point, approx. 5 inches from the
shorted
end. (exact measurements of stub length and tap point to be provided)"
Hi Paul,
Just heading out to work
this morning...remembered
this..
Please remember to send
a long this
info, at some point too. Great idea (looks like, from the
images..)
on cutting the shorted section of 450ohm ladder-line and soldering it
below
the feed-point. Makes for easy quick mods to the design!!
And, good morning too!!
73,
Steve
Hi Steve,
Ok, here's the
"skinny"...
the feed point is 4-in from
the short
the length of the matching
stub
is 16 in. on the braid side, 16-3/4 in. on the center conductor side
I was a little curious
about whether
putting the antenna "inside" the PVC would lower its resonant frequency
due to lowered VOP (velocity of prop.).
That's why I experimented
with
reducing the length, but as I mentioned, that only seemed to really
goof
up the SWR to become higher mid-band and lower at band edges, and also
not very good anywhere.
Let me know if I can
help with anything
else.
best 73,
Paul N8CVW
Hi Paul,
Did not know what text to
thin-out.
Soooo...posted it all.
http://home.comcast.net/~buck0/outpvccm.html
Hope this is okay with you
on this.
Seems we are both a little long winded too.
Thank you very much for
bringing
this experiment to the next level!!
73,
Steve KB1DIG
Hi Steve
Obsession got the better
of me,
so I upgraded to (4) 5/8-waves.
As you can see, PVC is
"vertically
challenged" at these lengths, so that has to be the end of it. Just a
slightly
noticeable improvement so far, in terms of hitting a repeater with 4
watts
that just wasn't there before without using more power. Also signals
from
W7EI, the 66 miles distant repeater, seem a little stronger. I'll have
to see if improvement under QSO is actually noticeable.
Just in case it's
difficult to see,
there is an additional 1" PVC strapped on as a brace. This puppy would
not get off the ground without it. I snapped it 3 times trying, before
adding the brace, and also using a "jin pole" for extra handling
support
as it went from horizontal to vertical. The jin pole is about 6-ft of
1"
PVC with a length of romex wire going through the pipe and forming a
loop
on the far end. This captures the mast, but then can be loosened to
uncouple
away once the stick is supporting itself.
The same dimensions were
used for
the tuning stub and the SWR reads the same. When I get a moment I think
I'll scout around for a PVC substitute that is more rigid. I strongly
expect
to find this antenna swimming in the pool if we get any strong winds.
73, Paul
N8CVW
Hi Paul,
Obsessions....;-) I'm
all
thumbs. These last few nights after work. Been trying to
connect
this blasted West Mountain Radio Rigblaster Pro to the Kenwood
TS2000.
The new soundcard interface gadget disables the internal TNC built into
the rig. It's not supposed to do that..
5/8th x4!!! So this
is what
pushing the envelope is all about. Wow!!
"vertically
challenged"...;-)
This reminds me of when I first tried to build a 6M halo out of 4 gauge
copper grounding. Didn't matter what support structure was added,
the thing just drooped. Ended up working with lightweight
aluminum
fuel line.
Nice mod with the reshaping
of
the phasing stub. They look like little mini-halos. I've
seen
some designs with the phasing stubs bent into a loop, but not like
these.
Interesting stuff!!
I will get all this new
stuff Web-posted
over the weekend too!!
Thank you!
73,
Steve
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