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k6sti
09-03-2015, 11:49 AM
I find aluminum tubing for low prices at local surplus metal dealers. But not everyone has such a place nearby, and they may not have the exact size or quantity you need.

Internet prices for new 3/8" aluminum tubing seem very high. For example, the cheapest I could find a 72" piece of 0.049-wall 6061-alloy tubing was about $24. That will make just one thin-wall element. An antenna with more than a few elements becomes expensive fast.

I found several places that sell and ship 3/16" solid aluminum rod for much less than 3/8" tubing. The cheapest price I found for a 72" piece was $3.16 here:

http://www.speedymetals.com/pc-2434-8368-316-rd-6061-t6511-aluminum-extruded.aspx

The 48" and 60" sizes are useful for shorter elements and cost even less. I didn't check shipping cost. They have a note that lengths 59" or greater incur additional UPS charges.

I think 3/16" 6061-alloy solid aluminum rod would be strong enough for an FM antenna. I've decided to optimize a Yagi based on these elements. Using 3/16" instead of 3/8" elements costs roughly 0.3 dB in forward gain and 1 dB in F/R. I think the cost savings are well worth the performance hit.

You can use 1" square aluminum for the boom, but this too is expensive. 1-1/2" PVC (1.9" OD) is much cheaper, can be bought at any hardware store, and eliminates the need for insulated element mounts. I don't think a 10-foot length will sag much, but it's easy to add boom guys if necessary.

I'm currently looking into designs that use 10-11 elements on a ten-foot boom. F/R will be at least 30 dB across the FM band and forward gain will be whatever I can get (currently 6.5-8.5 dBd).

If you're interested in building such a Yagi, speak up. If there's little or no interest, I'll drop the idea.

Brian

NN2E
09-03-2015, 12:35 PM
I've seen the VHF / UHF Hams use a piece of wooden closet pole inside of the PVC boom to add rigidity. Any holes drilled though this type of boom should be carefully sealed (you don't want the wood to soak up water) before the antenna is put into service. PVC caps can be used to seal the ends of the boom.

Brian... does the modeling program take into account the boom to mast assembly (clamp) and vertical (metal) support mast?

73, Ed NN2E
Owner / Operator - Murphy's Law Test Site & Thunderstorm Proving Grounds

k6sti
09-03-2015, 12:46 PM
The mast and bracket won't affect things unless they happen to be very close to an element.

I forgot to mention that the design will have three or four reflectors. Use a PVC Tee at the end of the boom and a vertical PVC piece to hold the reflectors. With this on the end, you may need boom guys.

Gain currently is 6.7-9.0 dBd across the band, which is not bad. 11 elements total, 4 reflectors, horizontal folded dipole. But two reflectors are 73" and the other two are 78". I think I will have to use a short center section of 3/8" tubing to get those lengths using 72" 3/16" rod.

Brian

NN2E
09-03-2015, 01:08 PM
Ah, OK, I had a standard Yagi design in my head... wasn't thinking of a multi-element reflector.

As you know, my one big issue with modeled antennas is, eventually, you have to take them out of the safety of the computer and put them to use in the real world. It's at this point the antenna system becomes the antenna plus it's environment. Most real world antenna environments introduce,"gremlins" into the performance of the antenna. This is where the disclaimer, "You're results may vary" comes in handy.

I look forward to reviewing your design.

73, Ed NN2E
Owner / Operator - Murphy's Law Test Site & Thunderstorm Proving Grounds

k6sti
09-03-2015, 01:18 PM
The only thing that makes much difference is ground proximity and other nearby antennas. I am currently optimizing this design in free space just to see what's possible. I may optimize the final design over ground since that's the way it will be used.

I don't know what to do about the long reflectors. A 12" piece of 0.058"-wall 5/16" OD tubing would allow a tight fit when used as a center section, but the place selling cheap 3/16" rod doesn't have that wall thickness. Everything else I've thought of is a kludge.

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17809

9.2 is 9 elements on an 81" boom. 15.12 is 15 elements on a 147" boom.

Brian

Danny
09-03-2015, 02:09 PM
Thanks, Brian. That all sounds interesting.

k6sti
09-03-2015, 02:19 PM
I had overlooked Speedy Metals custom cut service. Four 80" 3/16" rods are $16 total, or $4 each. Not bad and a simple solution to the over-72" reflector problem.

Brian

NN2E
09-03-2015, 03:25 PM
As I look around my antenna environment I see several things... a bunch of other antennas, several metal barns / buildings, house ductwork & wiring, metal vehicles, overhead power / phone wires, fence wires, guy wires...

On the RF side of things I see houses full of RF crud-producing devices, a cell phone tower site, a 100KW FM transmitter, a 57KW DTV transmitter...

... And I live out in the middle of nowhere. Throw all of the aforementioned into a bowl, along with your antenna, mix it all together and now you have some idea of what your antenna / receiver has to deal with. It's chaos out there!

My point is... If you build one of these antennas, and get weird results, don't blame Brian.

The charts & graphs look good, Brian. Now, who's going to be the first to build one? I'm not really an FM guy so don't count on me. :-)

73, Ed NN2E
Owner / Operator - Murphy's Law Test Site & Thunderstorm Proving Grounds

k6sti
09-03-2015, 03:47 PM
As I look around my antenna environment I see several things... a bunch of other antennas, several metal barns / buildings, house ductwork & wiring, metal vehicles, overhead power / phone wires, fence wires, guy wires...

Those things won't affect the antenna unless they are close to it. Large objects like metal barns can cause reflections, but that's another matter.

I'm trying to figure out how to make a robust folded dipole. The ideal way is to bend a single length of rod, but it would be too long to send through the mail. I think flattening the ends and bolting it together will have to do. But those connections are vulnerable. They need to be tight and waterproof. Accessing the center for feeding is also a problem since ideally it's inside the PVC boom. A model with one side in the boom and the fed side on the surface did not degrade performance, which surprises me. You have to support that fed rod somehow, but at least you have easy access for connections.

Brian

NN2E
09-03-2015, 04:19 PM
You're correct... the metal barns / buildings create lots of multi-path issues... A few years back the barn lost a section of metal roof during a storm. After this, local WPSD 32/6 would no longer decode using the indoor antenna system. After the missing section of roof was replaced, WPSD reception returned to normal.

If y'all want to try an interesting antenna / receiver vs. environment experiment...

Set up a portable FM radio in the middle of the room. Tune in to a weak FM station and then, walk around the room. Listen to what happens to the received signal.

In my 'shack' I have a 'Chairman Mao' brand FM receiver with a 30-ish inch (roughly 1/4 wavelength) piece of wire hooked to the antenna terminal. As I listen to local 95.5 W238AN Mayfield, KY I can walk around the room and 'tune' the system. If I stand in just the right spot W238AN disappears and WSM Nashville (100 mi) shows up. Move out of that spot and W238AN returns. Give it a try. "Your results may vary." :-)

Update 9-4-15... this morning I was able to receive KJEZ 95.5 Poplar Bluff, MO (110 mi) over local W238AN by standing in just the right spot, about 15 feet from the receiver.

Brian...I'll have to go out and stare at the antenna / aluminum pile to see what ideas come to mind, in regards to solving the mechanical issues, but it's too hot right now...

73, Ed NN2E
Owner / Operator - Murphy's Law Test Site & Thunderstorm Proving Grounds

Danny
09-03-2015, 04:48 PM
Ed and Brian, you both know I'm not an antenna expert.

Believe it or not, I've done the experiment Ed mentions with TV, FM, MW, and SW, using rabbit ears, long wires, and even the
front section of a large RS VHF/UHF antenna in the house.

My most recent experiments have been with rabbit ears in an attempt to decode DTV from my local KTAL-DT-15.

Ed is right.

My interest in Brian's and MW's FM antenna projects stems from the thought that I may get back into FM DXing again in the
future.

The FM-6 works well for Pat Dyer and Christopher, and it will work well for Mike P and amfm, because they are near the Gulf. It
may work well for many DXers elsewhere, in fact. However, I'm just far enough away from the Gulf, and inland where I have
stations between me and the Gulf, that my feeling is that I need a larger, more directional antenna. Fortunately, I have my
old, rebuilt Finco FM-5, and it is in good condition. Yet, that might not be enough to do the job here.

Therefore, down the road I might want to buy or build something more directional.

k6sti
09-03-2015, 05:05 PM
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Adding one more director. Since they only cost a few dollars, why not? But it hardly seems worth the trouble.

When F/R exceeds 30 dB, I have told the optimizer to treat the number as 30. Therefore, it doesn't try to improve F/R since it sees no benefit. Instead, it focuses on improving forward gain. This is one way of exploiting the fundamental gain-pattern trade-off that exists for all antennas. I could set the F/R target higher, but then forward gain would drop.

Brian

Danny
09-03-2015, 06:10 PM
Thanks, Brian.

k6sti
09-03-2015, 06:40 PM
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Here I added one more reflector and raised the F/R target to 32 dB, which it didn't meet everywhere. I'm not sure which design I prefer. Probably the 11 elements.

Maybe someone could suggest a good way to mount the folded dipole. I just realized that even the nonfed part has a problem. You must insert it through boom holes before flattening the ends. That could be awkward. Then you have to support the fed part somehow. Maybe it's time for some PVC joints and such.

http://www.homedepot.com/p/Charlotte-Pipe-1-1-2-in-PVC-Sch-40-S-x-S-x-S-x-S-Cross-PVC-02410-1200HD/203823993

The folded dipole for the 11-element design consists of two 3/16" rods 60-1/2" long separated 6-5/8".

Brian

NN2E
09-04-2015, 02:19 AM
I suppose the folded dipole driven element could be made from two 'J' shaped pieces. Two small holes would need to be drilled in the boom, as close together as possible. The two dipole halves would be inserted through the boom holes with a certain amount of overlap at the middle. The two element halves could then be clamped together, on each side of the boom, to hold the proper dimension and hold the element in place.

As for supporting the lower half (feed-point section) of the folded dipole... perhaps some plastic spacers / straps, slid over the upper and lower sections of each element half. The plastic oil containers and anti-freeze jugs are made from some pretty tough stuff and seem to last a while in the sunlight. A couple of straps could be cut from those containers with holes spaced at the correct distance to properly hold the driven element dimensions / support the lower (open) half of the element.

73, Ed NN2E
Owner / Operator - Murphy's Law Test Site & Thunderstorm Proving Grounds

k6sti
09-04-2015, 06:45 AM
The folded dipole is horizontal, not vertical. This orientation, introduced by Peter Körner, significantly improves antenna performance. Otherwise I'd use a simple dipole.

The horizontal folded dipole does not have to be exactly in the element plane, but if moved up or down the antenna must be reoptimized. The mounting method I like best so far is to mount each conductor on a small plastic rectangle on top of the boom. Hardware stores sell semicircular straps for 1-1/2" PVC that could hold the mounts to the boom as long as you add a screw to keep them from rotating. You could secure the folded dipole conductors with UV-resistant tie wraps through holes. I think this would work, but it seems kludgy and I'm still looking for something better. The folded dipole conductors are about 7-1/4" apart in the current design.

Another idea is to use #6 or #8 bare copper wire for the folded dipole. You can bend it at the ends, which eliminates four electrical connections, and you can solder to it at the feedpoint. I wonder if #8 would be self-supporting. Both sizes are available by the foot at Home Depot. The nonfed conductor could go through holes in the boom. The feedpoint conductor could be on top of the boom or perhaps inside if you cut an access hole in the boom.

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Brian

tripelo
09-04-2015, 11:18 AM
The folded dipole is horizontal, not vertical. This orientation, introduced by Peter Körner, significantly improves antenna performance. ...

Brian, what performance parameters does the horizontal dipole perform better (versus standard Folded Dipole)?

- Gain?
- Front/Rear?
- Bandwidth (frequency range that is acceptably impedance matched)?
- Other?

What do you think the mechanism (explanation) is that allows the horizontal folded dipole to perform better?

NN2E
09-04-2015, 11:29 AM
OK, so I was 90 degrees off... :-) ... It could still be attached by using the two hole, through the boom, overlap method on the 'closed' side of the driven element. The open ends of the element can be attached to / supported by a small piece of fiberglas dowel run through another hole in the boom. The 'overlap' section can be adjusted for 'fine tuning' the driven element length.

I've found the fiberglas dowels at Wally-World disguised as bicycle flags.... a pennant, on a long 'stick,' attached to a bike.

I've got a spool of #8 solid copper wire... I'll have to test it for rigidity.

73, Ed NN2E
Owner / Operator - Murphy's Law Test Site & Thunderstorm Proving Grounds

k6sti
09-04-2015, 12:00 PM
Just for reference, the folded dipole is fed at the forward conductor. Performance is much worse if fed at the rear.

I think the simplest way to support the rear folded dipole wire is to pass it through two holes in the boom with a tight fit. Some sort of adhesive can secure it, maybe even PVC cement. The forward wire can run in the same plane and then bend upward at the boom to its top surface, where it is split for feeding. I think two self-tapping screws on each side would hold it. At this low-impedance point they will have essentially no current so they should not affect performance. If you can do it quickly to avoid melting the boom, you can solder to the feedpoint after screwing the wire down. Otherwise, solder first and then secure everything. This is still a kludge, but a cleaner one.

I optimized a design using a folded dipole made of #8 copper wire. Then I checked the performance after replacing it with #6 wire. The difference was negligible. So if #8 will hold its shape when extended 30" on each side, it is the one to use. Otherwise, go with #6. The Home Depot website says the wire is available as soft drawn, in an intermediate hardness, and hard drawn. It's surprising they would offer so many choices. Maybe they just copied the manufacturer's blurb. Hard drawn would keep its shape best, I suppose. I may pay a visit to Home Depot today to see what they really have.

I haven't added up everything, but it looks like the material cost is less than $50 or so, not counting shipping or taxes. That's not bad for a high-performance antenna. The cost is higher than for a 5-element circularly polarized cubical quad made of PVC with about the same boom length, which offers even more gain in a circular field. But the Yagi has much better rejection of interference with unfavorable polarization. If you don't have much interference to contend with, the quad is probably the better choice.

Brian

k6sti
09-04-2015, 02:37 PM
I stopped by Home Depot. The #8 and #6 wire was out of reach on the top shelf. I didn't want to ask anyone to fetch it since I wasn't buying any. Let me know if you think your #8 is stiff enough. #8 was marked 33 cents/foot and #6 was 48 cents/foot. I thought those prices seemed awfully low. When I got back I checked the Home Depot website. They list 59 and 89 cents/foot. Must have been old prices on the shelf. Still, 59 cents/foot is about the same cost as the 3/16" aluminum tubing by mail. If it doesn't sag much, you might want to use it for all elements since you can get it locally. The diameter of #8 wire is 0.1285", which is less than 3/16" = 0.1875". May affect performance some if used for all elements even when reoptimized.

I checked out both ABS and PVC 1-1/2" pipe in ten-foot sections. PVC seemed a bit stiffer but was noticeably heavier. I think either would work fine. Not sure if boom guys are needed, but they are easy to make. I found nifty reducers and tees so that you could make the vertical boom that supports the reflectors from 1" tubing, which is 1.315" OD. That should be plenty large enough and would reduce weight and wind load.

I saw 1/2" ten-foot copper pipe (0.625" OD) for $9.48. Seemed cheap for all that copper and it was plenty stiff. The website gives the same price. One piece plus some wire to join the ends would make a folded dipole. Probably need your dowel idea at the feedpoint side.

Brian

More -

Using #8 for everything does degrade performance somewhat. I wouldn't do it except for the following: I just created a test order at Speedy Metals. Total material cost (no folded dipole) was $30.85, but shipping was $26.22 by UPS Ground to California. That's for less than 2 lbs. I think the shipping cost is way too high.

k6sti
09-04-2015, 05:07 PM
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This compares performance for elements of either 1/2" copper pipe (5/8" OD), 3/16" aluminum rod, or #8 copper wire. That red bulge is a bonus for the thick elements since the F/R target was 30 dB. If I had optimized longer it probably would have gone away, traded for an increase in forward gain.

You can make all 11 elements from eight ten-foot 1/2" copper pipes for a total cost of $75.84 locally at Home Depot. Using 3/16" aluminum from Speedy Metals plus something for the folded dipole from Home Depot costs somewhere in the upper 60s of dollars including shipping to the west coast. I'd rather go with the 1/2" copper for the improved performance plus the satisfaction of not paying all that shipping. If Ed says the #8 wire doesn't sag too much, that would be the cheapest option at about $37 from Home Depot with somewhat lower performance. Add the horizontal and vertical PVC booms and fittings, and that should be it.

Brian

NN2E
09-04-2015, 05:41 PM
All this talk of copper has me wondering... how tall of a tower will a meth-head climb in order to steal the copper? (I hope they never find out about the radials under my 160M vertical) It's probably just as bad, out there, as it is here... The meth-heads have been known to drive out into the country, use chain saws to cut down utility poles, (!) so they could strip the wire / transformers for the copper.

I wonder how galvanized steel conduit elements would model?...Not so hot, I'd imagine. Not really the best RF conductor. I've seen a few beams built from the stuff, though.

All along I've been assuming some things and I was wrong. My last assumption is the feedpoint connection... using a 4:1 transformer (balun) to go from driven element to feedline... correct?

I like Quad antennas... I had a hard time getting a reliable signal out of KFVS 12 Cape Girardeau, MO (70 mi) on my indoor antenna system. I tried a few different log-Yagi / regular Yagi antennas without any luck. I finally built a 6 element quad, designed for channel 12, and the reception problem was solved. For lack of a better term, quad antennas seem to be less, 'bothered' by their environments than the Yagi's.

When it cools off (it's 95F right now) I'll go mess with the #8 wire to see how well it holds it's shape.

73, Ed NN2E
Owner / Operator - Murphy's Law Test Site & Thunderstorm Proving Grounds

k6sti
09-04-2015, 05:54 PM
I wonder how galvanized steel conduit elements would model?

I actually had designed a very cheap Yagi using 1/2" conduit as elements. RF loss for zinc is negligible. But then I realized that the conductors are magnetic. I have no way to model what that does. I was afraid it would upset the element tuning. Conduit is ridiculously cheap. Ten feet of 1/2" galvanized conduit (0.706" OD) costs $2.30 at your local Home Depot! Eight of them for the Yagi would cost $18.40 total. The metal is soft and not strong, but it should be good enough for FM elements. It is quite heavy though (3 lbs each!). A PVC or ABS boom would definitely sag.

Yes, you need a 4:1 balun for the cheap Yagi. Halfwave coax baluns have by far the lowest loss.

Brian

NN2E
09-04-2015, 06:48 PM
Well, there's an, 'el-cheapo' way to build a Yagi... nearly the entire antenna could be constructed with little more than sections of conduit, a few pieces of 1/4 inch threaded rod (home-brewed 'U' bolts), and a box full of 1/4-20 nuts. Now we're thinkin' like Hams. :-)

I've used galvanized wire for MF / HF antennas (Beverages, dipoles & loops) and it seems to work OK. Not sure what'd happen with galvanized steel, up at 98 MCs, in a Yagi configuration, though.

73, Ed NN2E
Owner / Operator - Murphy's Law Test Site & Thunderstorm Proving Grounds

k6sti
09-04-2015, 08:10 PM
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I stumbled across my conduit design, which used nine elements on a ten-foot PVC boom. It's too heavy so I reoptimized it using 1/2" copper pipe. Total cost including the boom is $53.88 at Home Depot. There is just one reflector so no secondary boom. There is no folded dipole so no halfwave coaxial balun. Direct 75-ohm feed. But each element must be bent. This isn't difficult but it is tedious. Forward gain is comparable to that of the other designs, but F/R is about 4 dB worse. I'm not sure what I think about this design, other than I'm sure it would generate interesting conversation.

Total cost for the 11-element Yagi is $88.37 including the booms and all the PVC gizmos. I'm not sure 4 dB better F/R is worth $35.

Brian

NN2E
09-05-2015, 02:51 AM
I had a chance to, 'work' the #8 copper wire and I think it would be OK for antenna elements in a place where the weather isn't too extreme. (Not Kentucky)

Here's what KY weather does to antennas...

17851

... add to the ice storms, all the thunderstorms, high winds, hail, and Buzzards, Hawks & Owls that like to roost on antennas... I don't think the copper wire design would last long, here.

I lean towards building antennas that are a bit closer to, 'bomb-proof' so, the conduit antenna might be the better bet for areas with extreme weather.

Here you go, FM guys... the antennas you've been wanting... time to get to work.

73, Ed NN2E
Owner / Operator - Murphy's Law Test Site & Thunderstorm Proving Grounds

mwdxer
09-05-2015, 03:40 AM
Home Depot does have solid 1/2 inch aluminum tubing. It is not too expensive, not cheap, but buying a good FM yagi is out of the question at any price these days. I like the idea of a direct 75 ohm hookup without using a matching transformer. Here on the Oregon Coast #8 copper wire would not hold up too long. I would have to use at least #6 and maybe #4. Now that gets expensive and heavy.
By the way, is there some reason only round elements are used? Could you use square, or would that mess the gain and F/B up?

mwdxer
09-05-2015, 03:46 AM
Another alternative on getting a long boom is to buy a Ham antenna. I saw a 2 meter 14 element for $84. The boom is 15 feet long. The elements could be removed and redrill and install the right elements for an FM antenna. 15 feet would be plenty long. I don't know how big around the boom is, but that might work. It is a thought.

k6sti
09-05-2015, 08:45 AM
Thanks for checking the #8 wire, Ed. I completely forgot about ice. I'm sure there's no way the wire would hold its shape under an ice load. And unlike aluminum, it won't spring back into shape when the ice melts. I wonder how 3/16" aluminum rod would do in ice. My guess is that the sag would not be permanent, but I'm not sure.

Here is a link for 3/8" aluminum tubing that DXer Mark sent me. He used it to build a 10-element log-Yagi. This is the 0.058"-wall stuff hams use for telescoping, which is plenty thick for FM elements:

http://www.dxengineering.com/search/product-line/dx-engineering-aluminum-tubing/tubing-outside-diameter/0-375-in?autoview=SKU&keyword=tubing&sortby=BestKeywordMatch&sortorder=Ascending&N=360162%2B4294951161

Like Speedy Metals, the piece price is attractive but shipping and handling are high, at least to the west coast. Still, these prices are much lower than I've seen elsewhere. 72" is long enough for all elements for a conventional FM Yagi design. But it may be too short for the reflector for some designs. For example, the 11-element Yagi with four reflectors needs 75" and 76" reflectors if they are made of 3/8" tubing.

Brian

k6sti
09-05-2015, 09:31 AM
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This compares bent and straight elements for the 9-element Yagi. The FM broadcast band is just too wide for a conventional Yagi with one reflector, one driven element, and no other tricks.

Brian

Danny
09-05-2015, 11:25 AM
High winds are a problem here. In fact, ice is a problem. Freezing rain causes ice build-up on anything it touches, and it can
make antennas here very heavy.

I wouldn't use exposed copper outside at my location. It would be green in a short time.

Thanks for all of the good information being provided in this discussion.

k6sti
09-05-2015, 12:06 PM
Why would green copper matter, Danny?

Brian

Gary Hickerson
09-05-2015, 12:10 PM
"By the way, is there some reason only round elements are used? Could you use square, or would that mess the gain and F/B up?" (mwdxer)
Lightning, loves, sharp edges ! Round is better, for lightning and a little better, for ice.

Gary H.

NN2E
09-05-2015, 12:26 PM
Not a problem, Danny... the green oxidation won't bother it's performance... besides, the meth-heads will steal it before it has a chance to turn green.

Bending conduit isn't a big deal so don't be afraid to try it. Do all the bending BEFORE drilling... tubing tends to flatten / kink / tear at the drill holes when bent. A local muffler shop might be able to help you with bends. Another method of bending tubing is to tape over one end, fill the tubing full of sand, and then you can bend it without kinking it. When you've got it right, dump the sand out and drill the holes.

73, Ed NN2E
Owner / Operator - Murphy's Law Test Site & Thunderstorm Proving Grounds

Danny
09-05-2015, 12:26 PM
Why would green copper matter, Danny?

Brian

I thought it might affect performance.

k6sti
09-05-2015, 12:41 PM
Here's an interesting item at Home Depot:

http://www.homedepot.com/p/Crown-Bolt-1-2-in-x-96-in-Angle-Aluminum-1-16-in-Thick-41960/203122481

The equivalent cylindrical diameter is about 0.4". You could probably use it in place of 3/8" tubing without redesign. The 96" length is a bit awkward. For the designs I'm looking at, you can use one piece for the two shortest directors but the other elements need one piece each. You'll have a lot of aluminum left over when you're done cutting. The angle shape makes it awkward to mount to a 1-1/2" PVC round boom, which I think is the best choice due to its length, strength, and price. You could use these:

http://www.homedepot.com/p/Carlon-1-1-2-in-PVC-Conduit-Clamps-5-Pack-E977HC-CTN/202077414

or these:

http://www.homedepot.com/p/Cantex-1-1-2-in-Conduit-Strap-Bag-of-5-R5133734/202043359

Both are cheap. They may need a self-tapping screw to keep them from rotating. Even with that, it's not clear how stable they would be for this use.

The total cost for the aluminum angle bar is about the same as for 1/2" copper tubing, which comes in 120" lengths and lets you use one piece for two elements. Since it's more difficult to mount, I'm not sure the angle bar has any advantage. But it's the cheapest aluminum element material I could find at Home Depot.

Brian

NN2E
09-05-2015, 12:46 PM
Brian... would there be an advantage to using a larger diameter tubing for the elements? Lower Q? Broader bandwidth? ... might make for a more durable antenna. How would a larger diameter (metal) boom affect the performance? I'm thinking industrial grade construction, here.

I wouldn't be concerned with the weight of the antenna as long as I could make it as, 'bomb-proof' as possible.

73, Ed NN2E
Owner / Operator - Murphy's Law Test Site & Thunderstorm Proving Grounds

k6sti
09-05-2015, 12:58 PM
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Well, if you give up all element bends except for the driven element, it costs just 1.5 dB in F/R. This seems like a good compromise. It's much simpler than bending all elements. It's simpler and costs less than the 11-element Yagi with 4 reflectors. But you have to accept 5 dB less F/R.

Ed, larger elements help but they increase wind load and cost. The 1/2" copper is 0.625" OD. That's really quite large for the FM broadcast band where normally 3/8" elements are used. I'm sure it improves performance. A metallic boom doesn't matter as long as the elements are spaced away from it by 1/2" to 1" on insulated mounts.

I think a 1-1/2" PVC boom would withstand high winds if it is guyed. If you use nonconductive material, you can guy it four ways so it doesn't break in a severe updraft or sidedraft. A local ham lost an 80-meter Yagi in a storm that way. He had used only boom guys on top. He watched as the boom failed during a strong updraft.

Brian

NN2E
09-05-2015, 01:14 PM
Now, your local Ham knows what it's like to live here... It wasn't W6OAR, was it?

If I were building, I'd be willing to give up a little performance in exchange for durability. I'm getting old and tired of climbing towers. An industrial grade antenna would save on some of those trips up the tower.

I really need to take down my CS-1100 VHF antenna and make some repairs. Last Winter's ice didn't do it any good.

I also need to re-guy (Phillystran) the 130ft, 160M, vertical... who wants to help? :-)

73, Ed NN2E
Owner / Operator - Murphy's Law Test Site & Thunderstorm Proving Grounds

k6sti
09-05-2015, 01:37 PM
It wasn't W6OAR, was it?

No, but I can't remember his call. I only met him once or twice. But his story about the lost 80m Yagi really left an impression!

I just realized that using 120" lengths of 1/2" copper for the 9-element design leaves a piece left over that could be used as an element. So I'm optimizing ten elements on the ten-foot boom. The extra element probably won't increase performance much, but it's free. Looks like total cost for elements and boom is $53.88 at Home Depot. Not as cheap as I'd like, but it's affordable. I probably should figure out a good boom to mast attachment method as well. A flat plate with U-bolts always works, but there might be something better.

Brian

k6sti
09-05-2015, 02:38 PM
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Well, the extra element raised F/R about 1 dB. I'm going to see if I can fix the gain bobbles at the high end of the band, but otherwise I think this is pretty much it. I think I'm going to call it the Home Depot Yagi since that's where all the parts come from.

The design uses five of the ten-foot 1/2" copper tubes at $8.98 each. It uses a ten-foot PVC boom at $6.48. You mount the elements, which are 0.625" OD, by drilling holes through the boom. Secure them with PVC cement. The driven element needs to be bent in the middle at a small angle. I'm not sure of the best way to do that. Perhaps use short PVC struts to stabilize the angle. Direct 75-ohm feed with current balun (coiled coax or ferrite choke). The first and last elements are centered 0.75" from each end of the boom. Probably a good idea to measure the boom before bringing it home to make sure it's long enough.

Brian

k6sti
09-05-2015, 04:17 PM
http://ham-radio.com/k6sti/depot.htm

http://ham-radio.com/k6sti/curves.htm

Brian

mwdxer
09-06-2015, 03:10 AM
Is there some reason you are not using a pop rivet or a bolt to secure the elements to the PVC pipe?

k6sti
09-06-2015, 10:00 AM
If you think PVC cement is inadequate to secure the elements, use plastic bolts. Their length must be at least 2". If metallic, a bolt of this length may alter the effective element diameter and detune the element. In addition, over time the electrical connection between bolt and element may degrade. An intermittent connection may add RF noise, or in the worse case, RF intermodulation products. Nylon bolts should be black or painted black to resist UV degradation.

Brian

k6sti
09-06-2015, 10:44 AM
I have added an alternative design that uses the aluminum angle stock available at Home Depot by special order. Elements made of this 0.5" x 0.5" x 1/16" material should be much stronger than those made from 1/2" Type M copper pipe, whose wall thickness is just 0.028". (But the wall thickness of Type L copper pipe is 0.04". Also see the suggestion for reinforcing the copper elements with birch dowels.) You will have to figure out how to mount the L-shaped elements to the round PVC boom. If you decide to use a square metallic boom to make it easier, insulate the elements and mount them at least 1" away from the boom surface.

The angle shape is electrically equivalent to a round conductor with a diameter of about 0.4". See the writeup for curves that show the resulting performance hit.

http://ham-radio.com/k6sti/depot.htm

Brian

Danny
09-06-2015, 11:43 AM
Many thanks for all of the good information.

k6sti
09-06-2015, 11:59 AM
I added the Home Depot Yagi (copper elements) to the forward gain curves for the circularly polarized cubical quads. The five-element quad on a boom 4" shorter has higher gain for right-circular signals. It will also attenuate multipath distortion for these signals, receive vertically polarized signals, and is cheaper to make. The Yagi has a much better pattern for signals with nonideal polarization and will not attenuate right-circular signals that become left-circular upon ionospheric reflection.

http://ham-radio.com/k6sti/cpquad.htm

Brian

mwdxer
09-07-2015, 12:32 AM
With the elements on the PVC pipe, connecting them together with wire, wouldn't have affect the overall performance of the antenna? As a metal boom is one solid piece of aluminum.

mwdxer
09-07-2015, 12:40 AM
On the Oregon Coast that would not matter much as we have little ice and lightening is not common here. Would square elements effect the performance of the Yagi? I am very much interested in constructing a yagi like this. Using PVC pipe, is does sound feasible and would not break the bank. I am wondering about plastic bolts though, as wouldn't they deteriorate faster than metal? We have high humidity here and rest is an issue. Using aluminum solves that.

k6sti
09-07-2015, 12:24 PM
I reoptimized the 11-element design that uses multiple reflectors, removing the F/R target just to see what might happen. The pattern was so impressive that I decided to add the design to the Home Depot Yagi writeup. It requires eight copper pipes plus a secondary vertical boom to support the four reflectors. I would definitely reinforce the reflectors with dowels since they are quite long. See the end of the writeup for curves that compare the performance of the two designs.

http://ham-radio.com/k6sti/depot.htm

Brian

k6sti
09-08-2015, 08:08 PM
http://www.homedepot.com/p/Unbranded-1-2-in-x-10-ft-Copper-Type-L-Pipe-LH04010/100354232

I overlooked an alternative element material: 1/2" Type L copper pipe. It costs more, but the wall thickness is 0.04" instead of 0.028". Type L weight is 0.285 lb/ft and Type M is 0.204 lb/ft. More specs here:

https://law.resource.org/pub/us/cfr/ibr/003/astm.b88.1996.pdf

Brian

tripelo
09-09-2015, 01:07 PM
The folded dipole is horizontal, not vertical. This orientation, introduced by Peter Körner, significantly improves antenna performance. ...

Brian, what performance parameters does the horizontal dipole perform better (versus standard Folded Dipole)?

- Gain?
- Front/Rear?
- Bandwidth (frequency range that is acceptably impedance matched)?
- Other?

What do you think the mechanism is, that allows the horizontal folded dipole to perform better?

mechanism = explanation or why

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Repost-Original was delayed

k6sti
09-09-2015, 02:20 PM
The horizontal folded dipole usually improves the pattern more than forward gain, but my optimizer automatically trades one for the other so it's kind of hard to answer definitively. I don't know exactly why it helps. It offers another degree of freedom not available from a vertical folded dipole. That is, a change in spacing between the two conductors affects antenna performance when horizontal but not when vertical. But I think there's more to it than that because you don't get as much improvement by simply adding another element, which offers two additional degrees of freedom (length and position). The length of a horizontal folded dipole is always longer than expected for an isolated resonant element, the currents in the two conductors are dissimilar, and coupling to a close first director seems to matter. But it did not work as well as a bent dipole for the 10-element Yagi with just one reflector.

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These curves show the benefit of a horizontal folded dipole for a nine-element Yagi with three reflectors. Red is for vertical orientation. Green is for a 1″-diameter dipole with a 2.7° center bend and 7.8 pF across the 75Ω feedpoint. I used the same trade-offs and constraints to optimize each design. I would not assume this result is typical. Treat it as just one example.

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Another example. This compares the 11-element Yagi with 4 reflectors for horizontal and vertical folded dipoles. I used the same trade-offs and constraints. Gain is higher for the vertical folded dipole so the results are not directly comparable. For that, I'd reduce the gain trade-off and reoptimize so that the gain curves were closer. Then you could directly compare the F/R curves. But F/R for the vertical folded dipole wouldn't increase that much - it wouldn't come anywhere near that for the horizontal folded dipole.

Brian

tripelo
09-10-2015, 03:08 PM
...It offers another degree of freedom not available from a vertical folded dipole. That is, a change in spacing between the two conductors affects antenna performance when horizontal but not when vertical...
Yes.


...The length of a horizontal folded dipole is always longer than expected for an isolated resonant element, ...
Maybe so.

Looked at three driven elements using 4NEC2, modeled free space, all using 3/8” aluminum tubing. The lengths of the elements were adjusted to obtain lowest SWR at the band edges (88 & 108 MHz). The spacing between elements was somewhat larger for the Korner DE (3.9 inches) vs ordinary folded dipole (3.27 inches).



Ordinary dipole (`75 Ohms impedance, length end-end 57.7 inches)
Ordinary folded dipole (~300 Ohms), used spacing measurements from your Stellar Labs file (http://ham-radio.com/k6sti/stellar.htm) (length end-end: 55.3 inches).
Korner folded dipole (~300 Ohms), used measurements from your Korner 9.2 file (http://ham-radio.com/k6sti/korn92.htm) (length end-end: 55.1 inches).


The image below shows the forward Gain (dBi) and SWR of the three driven element configurations. SWR is referenced to 300 Ohms for the folded dipoles and to 75 Ohms for the ordinary dipole.


http://forums.wtfda.org/attachment.php?attachmentid=17921&stc=1

As might be expected, the forward gain of the ordinary dipole and the folded dipole appears to be similar. And, the bandwidth of the ordinary folded dipole is similar to the bandwidth of the Korner driven element. Although, the graphs shows increased forward gain for Korner driven element (~0.3 dB) as compared to the ordinary & folded dipole.


But I think there's more to it than that because you don't get as much improvement by simply adding another element, which offers two additional degrees of freedom (length and position).
Yes.

Some of the improvement may be the result of the driven element configuration since the regular Korner driven element shows forward gain compared to the other 2 driven elements. Both folded dipoles have essentially similar bandwidth.

The environment in the antenna (closely spaced other elements) could also account for much of its performance.

Interesting that the ordinary folded dipole also has gain compared to regular dipole, but the gain is in the vertical direction (straight down).

Below is a graph showing directivity comparison in the vertical (downward) direction. Here, it appears that the gain of the ordinary folded dipole in downward direction compares with the Korner driven element gain in the forward (horizontal) direction.


http://forums.wtfda.org/attachment.php?attachmentid=17922&stc=1


It appears, by laying down the folded dipole (Korner) takes advantage of the inherent directivity of the folded dipole.

Perhaps the folded dipoles could be considered as dual-driven elements. The end sections could represent the high impedance phasing line connecting the directly-fed front portion to end-feed the 2nd driven (rear) element.

If this is the case, the Korner dipole represents a front-driven ordinary dipole element with a 2nd element end-fed with considerable lagging phase close-spaced behind.

As you mentioned earlier, there are variables. The spacing between the front and the rear of the Korner obviously affects the pattern. Wider spacing might increase gain, but radiation from the end segments might increase sidelobes, etc. And the beat goes on. La de da da daaa :)


...the currents in the two conductors are dissimilar, and coupling to a close first director seems to matter...

The close spacing promotes high mutual coupling between the elements, the rear element is more closely coupled to the reflector than the front of the DE, and the front portion is tightly coupled to the director.


...But it did not work as well as a bent dipole for the 10-element Yagi with just one reflector....

Seems quite different, and interesting.

k6sti
09-10-2015, 03:53 PM
An isolated folded dipole has no special properties other than wide SWR bandwidth. But when used in a wideband Yagi, a horizontal folded dipole can increase forward gain and improve the pattern a surprising amount. You must analyze the entire antenna to figure out what's going on.

Brian

k6sti
09-11-2015, 05:37 PM
I've updated my writeup with dimensions for aluminum angle elements for the 11-element design. I think these elements should be stronger than either Type M or Type L copper pipe. They cost about the same as Type M. However, due to their smaller effective diameter, there is a performance hit. See the curves at the end of the writeup. I think I would use these elements if I lived where ice or wind was a problem. They must be special ordered so you can't just drop by Home Depot and check them out. Note that Lowe's sells a similar product for the same price whose thickness is listed as 16-gauge (0.0508"). Home Depot lists 1/16", which is 23% thicker. I e-mailed them to verify and they replied that the thickness is 1/16". I find both thicknesses listed elsewhere for similar products so I wonder what you'll get. But either is greater than the wall thickness of Type M (0.028") or Type L (0.04") copper pipe and the angle shape should resist bending.

http://ham-radio.com/k6sti/depot.htm

Brian

mwdxer
09-12-2015, 12:42 AM
This second yagi with the larger reflector on the back, looks along the same line as the Korner antennas. It looks like something worth looking into here, if I have to build my own. But I still wonder about the weight of the PVC pipe. What measurement changes would I have to make if I used a copper boom over the PVC boom? Copper piping is easy to buy at Home Depot. I may be able to get the plastic pieces from an old antenna or two for the dipole, etc.

k6sti
09-12-2015, 10:44 AM
What measurement changes would I have to make if I used a copper boom over the PVC boom?

You would have to shorten the elements by a factor of ten because copper pipe is much too weak to use as boom material. The recommended ten-foot ABS pipe weighs 2.7 lbs. The same length of PVC weighs 5.2 lbs but offers 32% greater flexural strength. It might be worth considering.

Boom weight hardly matters, but boom strength does. The simplest way to strengthen a boom is to add upper and lower boom guys. They can be made of steel wire. Add side guys to fortify the boom to lateral wind gusts. These guys must be nonconductive and you'll have to add a center nonconductive crossarm to support them. I think I'd go with just upper and lower guys and take my chances with side gusts.

For a truly rugged antenna, you'll have to obtain materials from somewhere other than Home Depot. I'd use a 1"-square thick-wall aluminum boom, 3/8" aluminum elements with 0.058" walls, and Stauff polypropylene clamps for element mounts. Use 6061 or 6063 aluminum alloy. The 0.4" equivalent-diameter dimensions for the aluminum angle should be close enough for 0.375" tubing. I'd try to find these materials at a local surplus metals dealer. A ten-foot boom would be expensive to ship because of carrier extra-length charges. If you have to order it from afar, it would be much cheaper to splice two five-foot pieces.

Brian

mwdxer
09-12-2015, 03:34 PM
Thanks. I would think you could clamp two 5 foot aluminum boom pieces together fairly easily. If I remember correctly some of the TV & FM yagi's I bought years ago clamped together and that way they were much easier to ship.

mwdxer
09-13-2015, 02:09 AM
The thin elements like on the FM6 sure aren't very strong. I would think any copper piping would be better than on a regular FM/TV antenna. I do know my old 6065 did not handle our high winds.

Gary Hickerson
09-15-2015, 06:54 PM
MW,
Its the "grade" of the aluminum, that determines, how strong it is. Channel Master used to use, "aircraft grade aluminum". They were Very strong. Cooper is fairly soft. it may work okay for a vertical ant., don't know about horizontal !

Gary H.

mwdxer
09-16-2015, 01:22 AM
I did not know that CM used to use that grade of aluminum. But the large booms on antennas seem to be pretty strong.

k6sti
09-16-2015, 04:00 PM
I stopped by Home Depot today to check out antenna parts. The Type M copper tubing was much stronger than I remembered. In fact, I thought someone had mistakenly put thicker Type L pipes in the bin, but all were marked Type M. The ten-foot length flexed a little, but nothing that troubled me. A 4-5 foot FM Yagi element should be plenty stiff.

I also checked out PVC conduit clamps for mounting the elements above the boom. This mounting method does not require drilling large holes in the boom, which makes it stronger and simplifies construction. The clamps are rigid, U-shaped, PVC pieces with mounting holes at the end of the U. Use two sheet metal screws to hold a copper element. Drill a small hole at the base of the clamp and secure it to the boom with another screw. Five clamps cost $2.13.

I located the thinner aluminum angle that Home Depot stocks. It is an eight-foot length of 1/2" x 1/2" x 1/20" material. It flexed some, but not badly. I'd use it as element material except that you can order it with 1/16" thickness, which will be even stronger. (For some reason the thicker stuff is cheaper.) You can mount aluminum angle elements to conduit clamps using sheet metal screws or screws and nuts.

If anyone is interested in a ten-foot Yagi for TV channels 7-13, I designed one using Home Depot parts. Total cost is about $36 for the elements, boom, and clamps.

http://ham-radio.com/k6sti/tv.htm

Brian

Gary Hickerson
09-22-2015, 12:29 PM
Has anyone, been, one of these, yet ?

GH

Gary Hickerson
10-01-2015, 05:51 PM
I meant to say, has anyone "built" one of these antennas, yet ? If so, had well does it work ?

Gary H.

k6sti
07-23-2016, 12:23 AM
After discovering how a critically positioned T-match can improve performance, I redid the Yagi made from parts available at Home Depot. I had to add a second reflector to fully benefit from the T-match, but the secondary boom is short. F/R now is greater than 30 dB across the band and forward gain is higher. I like this design a lot better than the original:

http://ham-radio.com/k6sti/depot.htm

http://ham-radio.com/k6sti/curves.htm

Brian