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post #4861 of 4874 Old 01-05-2016, 09:09 PM
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Hi all. I have perused much of this thread, admittedly not all of it.
I have relied very heavily "DIY TV Antennas" for a 4 bay. Sorry can't post the web link yet. Need 4 more post to do that. Works pretty good for being almost 60 miles from the transmitting antennas. Made some mistakes during the build. One intentional because I used as much of whatever I had on hand, and did not have to purchase. The 2 mistakes being I used chicken wire as a reflector because I had it. And then I mounted it to far back from the elements. I will fix those later when I make the next upgrades.

The test article was 4 pair of bow ties fastened to a 2x4 and leaned against the roof. Just 4 bowties, no reflector. Was really shocked at how well it worked. Now it is on a 20 foot mast (not a speck of wood in the build). I also made a single penny loop (with no reflector) atop the bowtie array for real channels 9 & 10, (23" loop). Tied the whole affair together with a 2 way splitter. With out a booster I get decent reception. Most channels show mid 80% range and a swr of around 23. A booster helps. Only when the weather turns poor does reception drop off to much. The uhf channels that I care about are 25, 35, 40 (these 3 the most) and 58, 64. All the rest are junk that you could not pay me to watch. Well how much pay are we talking about?

I put the whole thing up before I remembered pictures. Oh well. I used ¼” aluminum rod for the bowties. Much to spendy and hard to bend. 3 snaped.

I have sourced some 1/8” aluminum rod from Metal Depot at maybe a ¼ of what I paid for the ¼” rod. Also thinking about some stranded steel cable. Much cheaper yet.

Now my question. Where and how do I join extra arrays. I am planning on going up to 16 pairs of bow tie (at minimum 8). I want to do 8 on one section and 8 on the other. Shorter bow ties on one section that I can turn independently for the 2 high UHF channels (58, 64).

I am also going to replace the penny loop with a pair of folded dipole yagi's. If I use stranded steel wire I will have to support the lengths somehow.

Will continue to bring the two bands together with a splitter.

Thanks for any put.

Ken

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post #4862 of 4874 Old 01-06-2016, 09:19 AM
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The 2 mistakes being I used chicken wire as a reflector because I had it.
Chicken wire isn't quite as good as 1 x 2 wire fence, but you can use it if the twists are horizontal. The reflector should be 4-1/2 inches behind the elements.
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Tied the whole affair together with a 2 way splitter.
A UHF and a VHF antenna should be combined with a UVSJ, not a splitter in reverse as a combiner.

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Where and how do I join extra arrays.
With a splitter in revere as a combiner, with equal length coax lines, if it is two identical 4-bay UHF antennas.



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post #4863 of 4874 Old 01-06-2016, 06:18 PM
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Hi rabbit73 and thanks for the reply.

Just had a duh moment and realized that what I called chicken wire was really hardware cloth. My bad, just now realized it after all this time, I have been calling it the wrong thing. 1/4" square wire.

Thanks for the tip on the UVSJ. Did not realize that.

Oh and one more question. Should the reflector(s) be grounded or insulated on plastic stand offs like the active elements?

Thanks

Ken

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post #4864 of 4874 Old 01-06-2016, 06:23 PM
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Hi rabbit73 and thanks for the reply.

Just had a duh moment and realized that what I called chicken wire was really hardware cloth. My bad, just now realized it after all this time, I have been calling it the wrong thing. 1/4" square wire.

Thanks for the tip on the UVSJ. Did not realize that.

Oh and one more question. Should the reflector(s) be grounded or insulated on plastic stand offs like the active elements?

Thanks

Ken

"As for Me and My House, We Will Serve the Lord"
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post #4865 of 4874 Old 01-06-2016, 06:28 PM
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Sorry about the double post. New mouse with side buttons that my arthritic thumb knuckle keeps hitting. I lost the above post twice because of it. Can't disable it in software. I may disable it in HAMMER WARE.

Ken

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post #4866 of 4874 Old 01-12-2016, 11:28 AM
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Hi all,

Been reading all the DTV antenna threads with interest. I live in the Boston area, and recently became a cablecutter. I decided to homebrew a simple UHF antenna from scratch. (Since Boston is practically an all-UHF market, I concentrated on UHF reception rather than try to get the one or two VHF channels)

It uses 9" whiskers made from copper wire that is stretched between some small bolts on a piece of black foamcore board. The vertical separation of the whiskers is about 3", and the feedpoint spacing is approximately 1".

I made some intial tests with and without the 300 ohm balun at the feedpoint. There was no discernable difference in performance of quality, so I ditched the balun, since the feedpoint of a single bow tie is close to 75 ohms anyway.

The antenna is mounted on the highest indoor point on the second floor. This is fed to a TV downstairs by 35 feet of (93 ohm) RG62A/U. There are no apparent issues with the 93 ohm impedance of this cable, and since the feedpoint of the bow tie (nominally 75 ohms) varies according to frequency anyway, I can see no sense in worrying about an 18 ohm difference.

You can see I added some 5" whisker "extensions" using alligator clips. After some experimentation, the added length has stabilized any channels that were iffy. For whatever reason, this antenna beats a 4-bay version in terms of flexibility and performance, I "lock" about 30 channels with various sub channels - all rock solid. Not bad for some foam core and wire.
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post #4867 of 4874 Old 01-12-2016, 06:54 PM
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I've added a photo of the 4-bay version I made using the Mclapp-4 dimensions. Interestingly, there was no significant improvement over my "quick and dirty" single bow tie.
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post #4868 of 4874 Old 01-14-2016, 01:33 PM
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Originally Posted by Kenp51 View Post
Hi rabbit73 and thanks for the reply.

Just had a duh moment and realized that what I called chicken wire was really hardware cloth. My bad, just now realized it after all this time, I have been calling it the wrong thing. 1/4" square wire.

Thanks for the tip on the UVSJ. Did not realize that.

Oh and one more question. Should the reflector(s) be grounded or insulated on plastic stand offs like the active elements?

Thanks
From a PERFORMANCE viewpoint, it "shouldn't" make any difference whether the Reflector is grounded or isolated.

From a LIGHTNING PROTECTION point of view, it is better to ensure that there is AWG10 or larger wire from the Screen Reflector to the (presumably) METAL Mast....this will drain off any Static Electricity Charges that build up from wind passing across it (the higher the wind, the larger the Voltage)....the same way that Static Electricity can be built up by shuffling across a carpet. If the Antenna is the SAME Voltage level as surrounding Rooftops, it's less of a target than if it has a significantly DIFFERENT Voltage level which can ATTRACT Lightning Bolts.

And obviously, you can't run a "ground" wire to the ACTIVE Antenna Elements (e.g. Bowties or Folded Dipole in a Yagi).....but an OUTDOOR Balun (I've verified Channel-Master, Philips & RCA) SHOULD provide a DC path from the 300-ohm Twin-Leads to the outer Coax Shield to dissipate Static Electricity via that path to the mandatory Ground Block at the structure entry point.

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post #4869 of 4874 Old 01-15-2016, 08:47 PM
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Thanks holl_ands thanks for clearing up the reflector ground issue for me.
I picked up a ground block to attach at the pole base. I will run my coax down to it and then into the house. Right now I have one length of coax all the way from the antenna to the TV. Makes testing new parts a pain. Have to lower the whole thing.

I have made up up more bow tie >. Now assembling them. Also made up a pair of folded Dipoles for the vhf.

Be a bit before I can test.
Going to make up a angle pointer. and a spreadsheet for all of the info for the different channels so I can get accurate comparisons.

Ken

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post #4870 of 4874 Old 01-21-2016, 12:37 PM
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Another follow up question if I may?
The bow ties (4bay) I am now using are 9". I am going to add another 3 bays. Can I use a bay with shorter bowties, say 7"? That would be to get our two high channels, 58, and 64.

If so what should be the spacing of the bow ties? Tons of info for 9" and bigger, but I have struck out on finding anything for 7".

Is 7" to short for 58, and 64?

Will start assembling this bad boy after pay day. A few more things to buy.


Here are some pics of what I have so far. The vhf folded dipoles elements are ran through a fiberglass arrow shaft to support them. all the elements are tightly twisted steel wire. Gives it a much greater cross section, as well as makes it some what stiffer. Still need the arrow shaft support though.
Yeo one of the bow ties had a mismatch in element size. I caught that looking at the pics. Already fixed that. http://s1281.photobucket.com/user/ke...tml?sort=3&o=0 The mounting plates are just plastic cutting board from Wal Mart. 99 cents each and then cut into strips on the band saw. 1/32 threaded rod cut into 1' lengths for bolts and left over scraps of plastic board cut into square washers.
http://s1281.photobucket.com/user/ke...tml?sort=3&o=2 http://s1281.photobucket.com/user/ke...tml?sort=3&o=1
The original bow tie I made was much more expensive to make. I used 1/4" aluminum rod. Man is that stuff hard to bend 270 degrees or there abouts. Broke 3 rods before I figure it out. Rods were about $4 each and if no breakage yielded 2 elements. Then the fasting bolts and nuts ran me more $ yet.
I will have another 12 element pairs for less than I spent on the first 4.
The most expensive part in this added build are the arrow shafts, and square aluminum rod.

Ken

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post #4871 of 4874 Old 01-21-2016, 02:30 PM
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That would be to get our two high channels, 58, and 64.
All channels above 51 are no longer in use for TV broadcasting. Those are "virtual" channel numbers (the old analog channel number, specifically), you must look up their "real" or "RF" channel in order to determine what element size would be optimized for them. Those two Sacramento-area stations broadcast on channels 46 and 26 respectively.

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post #4872 of 4874 Old 01-21-2016, 03:00 PM
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Real Ch26 is on 545 MHz and Real Ch46 is on 665 MHz. You can't simply pick a Whisker Length and hope for the best....the overall design, including Bowtie Spacing, Feedline Separation (which increases OVERALL Width) and Separation to Reflector must be JOINTLY Optimized as a complete, interacting SYSTEM.

Your best choices would be the M4 (10x9.5) or Free-Form FF4 [4-Bay with DIFFERENT Element Lengths]....or FF6 (6-Bay) which has an extra BUMP close to Ch26 for the FLATTEST overall frequency response:
http://imageevent.com/holl_ands/multibay/4bayrefl

Or a Pair of Vertically Stacked M4 (9.5x9.0) [I haven't yet run Optimization for M4 (10x9.5)], or a pair of FF4's...or a pair of FF6's all of which have fairly FLAT frequency response:
http://imageevent.com/holl_ands/stac...allystackeduhf

You didn't explain HOW you would Combine them, but if they are pointed in the same direction, they all need to be MATCHED wrt Gain and Phase....which means identical construction....and you would need to JOINTLY RE-OPTIMIZE a mis-matched combination to minimize SWR problems and Cancellation NULLS.

BTW: To combine two DIS-SIMILAR Antennas (e.g Hi and Lo-Band UHF), you should use a Join-Tenna (or equivalent), which is a pair of Bandpass/Bandreject Filters that isolates the effect of one Antenna on the other....similar to a VHF/UHF Band Diplexer (aka Combiner/Splitter)....so it's more cost effective to use an Optimized Design from the start. You would ALSO have to construct an Antenna Optimized for Ch26, which would involve changing ALL of the Dimensions for one of the existing Antenna Designs and making them BIGGER by approx Rescale Factor = 681/545 = 1.25.




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post #4873 of 4874 Old 01-22-2016, 09:53 PM
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Dang it I pulled a silly. I made a spreadsheet of all the relevant channels to me. Their virtual and real channels., broadcast frequency, etc.
I transposed the real and virtual channel numbers for 58, 64. Thanks for pointing out the real numbers for me. Geez garbage in , garbage out.

I stumble onto a gold mine today. Found a old mostly busted up tv antenna today, intwined into a grape vine. I cut it out of there. Lots of square aluminum tube. 2 50", 2 18", and a 60" piece of 1"square tube. All the tube is in decent and usable shape. Gold mine. Would not have found it if not for chasing the neighbor's chickens back across the fence.

I will order a Pico Macom UVSJ UHF VHF Band Separator/Combiner for Antenna (UVSJ)
http://www.solidsignal.com/pview.asp?p=uvsj

Ken

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post #4874 of 4874 Old 01-29-2016, 08:58 PM
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Thanks holl_ands
That reference you posted is exactly what I am building
I have to get some flat stock aluminum to extend the 50" tube 3.5" each end to get the correct spacing for the end elements. Also have to get more cutting board as I had already cut them based on the original antenna I built. That had 1.25" phase line separation, this 1 is 3 I see after printing it out. No big deal.
To make this thing cheaper I am cutting threaded rod into studs versus pay threw the nose for bolts. I guess I need to stand my plastic mount plats off the aluminum spine at least an inch to keep the space lines from being to close to it and thus ground.

It is slow for me because I am also working on other projects (a fence that fell down. that and my disabilities really slow me down and limit my endurance.

Will report at completion and with some pics.

Ken

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