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Discussion Starter #1
This is a thread for descriptions/photos etc.. of home-built yagis for O.T.A. television reception. Or whatever.

The first yagi I ever built, last spring, was a 10' long model, designed for UHF 23. It used a length of 3/4" thick wall square aluminum tubing that I found at a surplus shop, with 5/16" aluminum rod elements isolated from the boom.

The driven element was a small folded dipole made from 10AWG copper wire, connected to a commercial 4:1 balun.

It worked great for virtually all of our local channels, including 60, 43, 25, 24, 22, 14, 13, 11, and even 6.

But not the distant 23 for which it was designed. Our GH10s and PR-8800s outperformed it at this location.

This yagi has since found a new home where pulling in UHF 23 is much more feasible.
 

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Discussion Starter #2
This past summer, I had opportunity to construct a VHF yagi, for use by a family friend at her cottage. She wanted to be able to watch the 2008 Olympic Summer Games there, which was broadcast on the local CBC station on VHF channel 8.

The antenna was installed indoors, so robust construction was not a requirement.

We used some surplus rectangular aluminum tubing for a boom, about 9' long, with 7 directors, one reflector, and a folded dipole as the driven element. All of these were fabricated from 5/16" aluminum rod.

With this antenna, I decided to try bonding the passive elements to the boom, by wrapping them with small tabs of aluminum sheet metal, and pop riveting the results to the boom. But alas, the boom had some kind of coating on it, so the results were not as good as hoped for, though the pop-rivets certainly helped.

A commercial 4:1 balun (standard TV matching transformer) was used to suppy the RG-6 downfeed to the set.

This antenna works spectacularly well, given its suboptimal positioning inside a cramped atic crawlspace.
 

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Discussion Starter #3
A yagi for UHF 24

Another season, another yagi. This one was built today in our basement workshop, and is currently up on the tower.

As with earlier yagis, I used the k7mem yagi Antenna Quick Designer web page for the calculations. The boom is a 58" length of 3/4" square aluminum tubing, and the passive elements are all made from 1/4" round alumimum rod. Quite cheap stuff, all of it from our local Metal Supermarket.

I decided to try for bonded elements again, but in a much more robust fashion than the previous attempt -- this antenna is going outside in the elements.

A diamond stone was used to slim down a 1/4" spiral drill bit to smaller than normal diameter. The boom then got cross-drilled with that bit to accept the 1/4" diameter passive elements. This made for a very tight pressure fit on assembly, with a certain amount of persuasion (hammering) required. And for good measure, a single long aluminum pop-rivet was applied in the center of each element (from the bottom). This should make for a sturdy and weatherproof antenna.

For the driven element, the 1/4" rod kept breaking when I tried to bend it, so we switched over to 5/16" rod and bent that into a folded dipole design.

This time, rather than using a standard commercial 4:1 balun, I had a go at making my own: a simple coax loop balun, as described by k7mem near the bottom of this page. When properly constructed, this should eliminate the usual 1-3dB insertion loss from commerical baluns, for the design channel at least.

The trouble was finding some 75ohm coax with a solderable (copper) braid.. I have about 700' of RG-6 on a spool, but it uses aluminum foil and aluminum braid inside -- can't solder to that!

But deep in my bin of antenna cast-offs, was a meager 10' section of old RG-59/U, with copper over aluminum foil for the shield. Yay!

The whole deal was assembled into a 2"x3"x1.5" plastic box, with rubber grommets on the holes, and an F-connector on the outside for direct connection to the RG-6 feedline.

And the darned thing actually *works*! Perfect reception of channel 24, plus some others.

Channels 60,65 are fuzzy, channel 43 is grainy, digital 25,22 are perfect (of course), and UHF 14 is also pretty good.

But.. even VHF 13 and 6 are quite decent with this antenna. Not perfect mind ya, but not bad.

Detailed photos later, once I take it back down for reconfiguration (see next post).

Cheers
 

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Discussion Starter #4
Here's the UHF 24 yagi:



And a closer view of the business end of it:



I'll post more detailed construction photos and stuff next time I have the antenna down off of the tower.

Cheers
 

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Nice looking yagis, mlord.

Another good free downloadable yagi program is the Yagi Calculator by John Drew (VK5DJ).

This should make for a sturdy and weatherproof antenna.
Since both ends of the boom are closed, I would drill some small weep holes in the bottom of the boom, to let out any condensation.
 

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Discussion Starter #6
The drain holes, in both the boom and black box as well, are *already there*.

I'm planning another yagi (or two), and I'll post construction details and photos as that one gets built.

Cheers
 

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Discussion Starter #8
Yeah, that's it -- just beyond the inside edge of the inserted end-plug. There's a drain at the other end as well, plus one in each of the four corners of the connection box.

Despite it being very difficult for moisture to get inside either the boom or the box, I know from geocaching experience that water *always* gets in, eventually. :)
 

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Discussion Starter #9
How to cut rod segments quickly and accurately

These yagi antennas require a lot of accurately cut rods, with UHF tolerances being around 1.5mm on the lengths. I generally do better than that, with everything within 0.5mm deviation from spec.

This is easy to do with the right tools.

First, I mark the desired length on the rod with a fine-tip marker, and then use an el-cheapo bolt/chain cutter -- looks like 2' long cutting pliers -- to lop it off to rough length, say within 5mm or so of the mark.

Then I use a right-angle jig (mitre-gauge) in combination with a disc-sander, to quickly sand the ends down to exact length. Achieving 0.5mm accuracy is pretty easy this way.

One could do it using a file instead of the disc sander, but it would take longer.

Another option that I used once, is the very accurate mitre gauge on our cabinet saw (tablesaw). Extremely quick, clean, and accurate, but hell on blades. Sure, carbide can cut aluminum just fine, but it does dull the teeth rather quickly. Which spoils the blade for other, more demanding uses.

Cheers
 

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Despite it being very difficult for moisture to get inside either the boom or the box, I know from geocaching experience that water *always* gets in, eventually.
Yep, if from nothing else, condensation. Its cool at night and when it get warmer in the morning, condensation forms. Over time, a lot of water can collect in a semi-sealed area.

Sure, carbide can cut aluminum just fine, but it does dull the teeth rather quickly. Which spoils the blade for other, more demanding uses.
You could try the old aluminum siding trick. Put a plywood, non carbide saw, in backwards on the table saw. It cut the aluminum siding smoothly without catching into it and making jaggies. It should work well on aluminum rods too.
 

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Discussion Starter #14
Another day, another yagi: detailed construction photos.

The UHF-24 yagi now has a buddy below it: a VHF-11 model, with about 9dBd of real gain on a short 56" boom. These two antennas share a single RG-6/U feed (no pre-amp) using a UHF/VHF band separator/combiner, visible in the photo below.



Some construction photos/details are here.

The rotor is temporary, to ease figuring out the best aiming (now done!).

Two more to go now. One for VHF-13 & VHF-6, to replace a horrible dipole kludge that's still working well after 15 years, and then another LONG boom yagi to try and pull in distant UHF-38 on a good day.

Cheers
 

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i see trees in the background

Those yagis look really well built. I cant tell what preamp you are using from the closeup pic, but I assume it's got a good solid 20 dB gain or so. Im surprised you cant get 23 with a long yagi like that, with no buildings blocking the way.

It could be the trees, however. I would like to do an experiment to see how much better a preamped dipole 20 feet higher than the preamped yagi would do. A dipole is light enough to be able to get height. It would be interesting to see the trade off. I have a suspicion an extra 20 feet might equal an extra 20 dB of gain at UHF, especially in getting over the trees.
 

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Discussion Starter #16
No pre-amp at all on these yagis! The little box is just for the feedline connections and coax-loop balun.

At our location here, Cedar Hill (Barhaven) is higher ground than us, blocking a direct path to WNPI. But we do get WNPI-DT most of the time on the dual PR8800 array, so I'm not going to do much more about it unless things worsen.

Hopefully they'll get their little ERP bump come February, and reception will even improve a little bit.

Cheers
 

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Discussion Starter #17
Sigh.. another day, yet another yagi.. VHF 12/13.

This is the final new yagi for our forest devoted to local broadcasts. It was designed for the low side of VHF-13, and should serve to pull in VHF 6 (someday moving to 12) as well.



It's definitely on the short side, at about 45" in length, but should have no difficulty with the stations in question, which we currently obtain from a really crappy low-VHF dipole on a mismatched feedline. :)

It's going up on the tower Real Soon Now.

Cheers
 

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It could be the trees, however. I would like to do an experiment to see how much better a preamped dipole 20 feet higher than the preamped yagi would do. A dipole is light enough to be able to get height. It would be interesting to see the trade off. I have a suspicion an extra 20 feet might equal an extra 20 dB of gain at UHF, especially in getting over the trees.
Plugging in different height numbers in TVFool will give a good approximation of that. Plus add in another additional 3 to 9 db when finally reached over the tops of trees, (value depending on the type of tree, the higher number if firs).
 

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Discussion Starter #19
GerryB said:
I would like to do an experiment to see how much better a preamped dipole 20 feet higher than the preamped yagi would do.
Heck, the UHF-24 dipole here hardy weighs anything at all. Something that size could go up very high on a pole if we wanted.

The one problem with where the tower here currently sits, is that there's no way to guywire anything like a long pole on top of it -- too close to the lot line to stretch a guy out that way.

Meanwhile.. the VHF-13 yagi is now up on the spare mount, and works perfectly for 13, 14, 24, and 43. It even does a respectable job on 11, despite being pointed in entirely the wrong direction for it.

But no good for VHF 6, and merely "okay" for VHF 4. I suspect this has more to do with the channel-specific coax-loop balun than with the antenna itself. We don't care about 4 (there's a UHF digital version available), but 6 is important for a couple of years yet, before it transitions to digital on 12.

I'll take that yagi down again in daylight (frikken cold up there tonight!), and wire in a standard commercial 4:1 balun to see if that fixes reception of VHF-6.

Cheers
 

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mlord, very nice antennas, really well built and designed. They even look better and sturdier than some commercially available Yagis. Great job ! And your step-by-step instructions are very appreciated.

I would hope to have metal depot around here (Montreal), but it looks like the big surfaces are the only available option, with very few economic choices (like threaded rods).

Edit: How are you gonna connect all those yagi together ? Wouldn't there be multipath problems ?
 
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