KB1DIG's 5/8th Wave Colinear
"Outside PVC" 2 Meter Design Comments:
Tuesday, August 29, 2006 11:59 AM
Subject: Re: 5/8-WAVE COLINEAR "OUTSIDE PVC" 2-METER 146 MHz FM J-POLE
Great web page!
I just built the outside PVC 2-meter antenna and it turned out great, I've attached a couple of photos.
I did a couple of things different; instead of copper wire I used 9 gauge-galvanized general-purpose wire. It was about 6 bucks for 50 feet of it at Lowe's. And used a 4 pin Square D grounding block, cut in half to terminate the galvanized wire to the coax. I also PVC glued on an extra two feet to attach it to my mast and ran dowels the whole 12 foot length to stiffen it.
SWR is great anywhere from 136 to 150 Mhz was an SWR 1.1:1 from 150 to 164 around 1.3:1 to 1.7:1. Reception was great about 3 db over my old copper cactus jpole (not stacked), got access to 20 more repeaters verses the old antenna.
Just for kicks I loaded it up on 70 cm, SWR was also good 438 to 452 was around 1.1:1, reception was marginal on 70 cm, to be expected.
I've built many j-poles, this one is the easiest and a good performer.
Friday, January 07, 2005 8:04
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
Thanks for checking out this design.
Not sure if you have
seen this Web-page
(for the same design) too.
Great idea with the
Check this link out.
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.
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.
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
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....;-)
and I get some really interesting e-mail from our Hampage...
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!!
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.
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.
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!
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.
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
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)"
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!!
Ok, here's the "skinny"...
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
putting the antenna "inside" the PVC would lower its resonant frequency
due to lowered VOP (velocity of prop.).
Let me know if I can help with anything else.
Did not know what text to thin-out. Soooo...posted it all.
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!!
Obsession got the better
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.
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!!
Date: Thu, 25 Nov 1999 00:47:50
From: "Steve W. Merrill" <email@example.com>
I checked out your repeater page and saw that you were working on the
5/8x2 2M j-pole. So, how did it go? I took some images of this antenna
and added them to my page a few weeks ago.
I don't know if you have seen these. I have had good luck with the one I
did. Let me know if you need help working out any problems. You are
the only person I know that has attempted to build this thing, other
The images on your index page did not come up.
I hate that when it happens. I think the problem is that a file is
missing on your server. "rule18.gif" You might be able to see this
image from your home computer. Welcome to the wonderful world of HTML.
The file is probably being accessed from your hard drive when you review
the page from the web, after uploading. I know when I did my page I had
to fiddle fart around to keep that from happening. Other than that, it
looks really great.
Keep me posted!
Steve KB1DIG :-)
Date: Thu, 25 Nov 1999 01:13:47
From: "Steve W. Merrill" <firstname.lastname@example.org>
A quick note about "TVI at my in-laws house."
When I tested the "Inside PVC" 1/2x2 2M
with more power then 15
watts it caused some strong TYI (and over the computer speakers, and
over the clock-radio...) at my home. The "Outside PVC" 5/8x2 2M
antenna, I can run at 50 watts all day long without any TVI at all.
Hope this info helps.
Date: Thu, 25 Nov 1999 09:27:16 -0500
To: "Steve W. Merrill" <email@example.com>
The j-pole works quite a bit better than the
did. I haven't built one
for the receiver yet, it's on the list of things to do. I can hear the antenna
25 miles away from a mobile. I am running it at 50 watts, and its only 30' AGL.
I am in the process of closing down the QSL website. You can go to my page at
http://kf4pxz.members.atlantic.net . There is more information as well as all
of the pictures & graphics work. I am also placing a link to your page there.
Thanks for the interest and comments.
Happy Holidays, 73 RJ Glenn KF4PXZ
to the 5/8-WAVE COLINEAR "OUTSIDE PVC" 2-METER 146 MHz FM J-POLE page.