How to build a UHF antenna... - Page 10 - AVS Forum
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post #271 of 4798 Old 06-04-2008, 12:21 AM
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Maybe I'll mask off the elements, and paint the 2x4 as well!

Masking is a pain. I would think removing the elements, then paint, then replacing the elements would be easier and neater.
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post #272 of 4798 Old 06-04-2008, 07:40 PM
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As 300 ohm said, if your using wood I'd suggest painting it first before installing the elements or phase line.

Stay away from silver paint, or any other metallic paint as it may contain some metal particles in it. Since all the elements are driven elements in a 4 bay you'll short out the whole thing.

White is a good choice, clear coat would be good too. After you have the antenna assembled an overall coat of non-metallic paint would be fine.

By the way 300ohm your double hoverman looks really nice and I'm sure it performs as well.

tombobiche the 8 bay I have up only very slightly out-performs the 4 bay when mounted in the same place. It's an experiment using a different feed system I'm going to take it down soon to try something different but I'm concentrating on the 4 bay right now. As you saw that reflector makes a huge difference in the 4 bay.

Any one who has built one of these 4 bays using the dimensions I posted let me know how it's working, post some pictures. The more I can learn from people using these the better chance I have in tweaking the design for best results.

Has any one tried the 15" reflector spacing for enhanced VHF-HI reception?

I tried it on my wooden test mule and it worked well, a noticable improvement on some VHF-hi stations and no noteable change in UHF.
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post #273 of 4798 Old 06-04-2008, 07:54 PM
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mclapp and others who have given advice i finally got my four bay put together....
now to figure out the reflector.. By the way im doing a single hoverman too...ahh
work in progress.. let you know how it all works in the next few days.


John

EDIT

OK i took it outside no reflector on the four bay its pulling two scranton stations vhf wbre and wyou lol wskg wbng wicz out of Binghamton now i need to go and get some reflector material.
these are all below threshold about twenty five thirty percent..

By the way i ordeded a vhf high band yagi from solid signal see
how that puppy does it was a five element antenna craft cheapie
I cant wait to toss the cable


JOHn
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post #274 of 4798 Old 06-05-2008, 11:00 AM
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I retested the reflector using these horizontal bars and 2X2" chicken wire behind it as a quick and easy reflector. It works really good and was up late night on Fox 33 watching a Catherine Deneuve movie. I tried bending it like the channel master and got no better results than flat. But my advice is if you can get the 1X2" mesh in light aluminum or stainless then use it as mcclap's dimensions in 36X40", that makes for more dbs.
I figured out how to rig the mast. I'll drill two holes through the reflector supports and then screw the steel pipe into the back of the upright wooden support; that will make it very strong, then since the pipe is about 12 feet long, bolt two pipes together in the middle side by side. Then it can be dropped into a swivel or simply buried in the ground, and any top support can be adjoined to a stucture or fence. Then it can be rotated with pressure pliers for remembering stations.
Heres a Rhomic with lengths no more then 55". Ive never tried this and doubt it can beat our bowtie/Hoverman endeavors but maybe it could work. Rhombic goes the size of the yard without rotations. Ive seen tabletop mini rhombic amplified systems.
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post #275 of 4798 Old 06-05-2008, 04:32 PM
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Heres a Rhomic with lengths no more then 55". Ive never tried this and doubt it can beat our bowtie/Hoverman endeavors but maybe it could work. Rhombic goes the size of the yard without rotations. Ive seen tabletop mini rhombic amplified systems.

Well, that one is only about 4 - 5 wavelengths per leg long. IIRC, rhombics generally only get good with around 10X wavelengths per leg long. But I also recall seeing rhombics like that stacked 3 high that claimed something like 25db gain. (Seeing in an article design drawing, not in real life) They can get to be monsters.

Building something like that could be done with hard copper 3/8 ID inch (what that plan calls for) or 1/2 ID inch copper pipe, but it would get very expensive now, if youre buying new hard copper pipe. It could also maybe be made using 1/2 inch pvc pipe, and then stretch the wires inside of that form.
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post #276 of 4798 Old 06-05-2008, 06:22 PM
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Quote:
Originally Posted by 300ohm View Post

IIRC, rhombics generally only get good with around 10X wavelengths per leg long. But I also recall seeing rhombics like that stacked 3 high that claimed something like 25db gain

Now THAT I would love to see (not that is practical, or anything

http://rochestermnhd.blogspot.com/ - Tech 55901. Tech news for Rochester. Authored by mattdp and gjvrieze.
http://tvfmantennas.a.wiki-site.com/index.php/Hardware
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post #277 of 4798 Old 06-05-2008, 07:23 PM
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Originally Posted by johnied View Post

mclapp and others who have given advice i finally got my four bay put together....
now to figure out the reflector.. By the way im doing a single hoverman too...ahh
work in progress.. let you know how it all works in the next few days.


John

EDIT

OK i took it outside no reflector on the four bay its pulling two scranton stations vhf wbre and wyou lol wskg wbng wicz out of Binghamton now i need to go and get some reflector material.
these are all below threshold about twenty five thirty percent..

By the way i ordeded a vhf high band yagi from solid signal see
how that puppy does it was a five element antenna craft cheapie
I cant wait to toss the cable


JOHn

Well now you know the signals are there which is how all this started right.

A reflector on that 4 bay will be a big improvement.

How high did you have it?

If you get the 4 bay finished with the large reflector it would be interesting to see how it stacks up to the high band yagi.

I'm positive it will be some amount less but how much less would be interesting to know.

If you want to make a quick and easy reflector that will work almost as good as screen I have something for you to try.

What you'll need is something to make a frame 36" x 36" and about 65ft. of wire. The wire can be anything steel, aluminum, copper and any gage coated or uncoated.

(1) Make a frame out of wood or metal so that you end up with 2 vertical uprights 36" high and 36" apart.
If the frame is made of metal using bare wire would be best so that the frame can also be an integral part of the reflector.

(2) Drill holes the size of the wire you have 2" apart the entire length of the vertical frame members

(3) Start at the very top and string wire back and forth between the frame members all the way to the very bottom so that you end up with wires running parallel 2" apart horizontally. It's ok to splice multiple pieces of wire together just try not to do it on a horizontal section.

Center the grid 14" behind the phase lines of the driven elements.

This is not as good as the angled wire mesh reflector but it's pretty close about 1-2 db less on UHF, and could be much cheaper especially if someone had some scrap wire kicking around.

Someone could make an angled version with some extra frameing.

Have Fun
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post #278 of 4798 Old 06-05-2008, 11:56 PM
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Here a link to the web page:

http://www.tvtechnology.com/features...5-f_doug.shtml

"On p. 35, there is a description of DHR (dual hexamerous rhombic) antenna designed for the 430 MHz band. It should work well at UHF frequencies. The calculated gain of the 2x6 rhomboid antenna is 33 dB! "

Heh, what a monster. Good luck finding a rotor for it.
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post #279 of 4798 Old 06-06-2008, 11:20 AM
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Quote:
Originally Posted by [B View Post

fbov[/b]
I trust you used non-conductive paint ...

Not sure , I better check!

hyghwayman

Ok after checking I found it was indeed metalic crome paint.

Thanks for asking!
hyghwayman

Just my 2¢ - take it or leave it for others

 

 

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post #280 of 4798 Old 06-06-2008, 12:45 PM
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One never knows when the odd thought passing through one's mind might be an "oh sh*t" passing through someone else's ...

And I'd like to add a brief word of thanks to those who read and contribute to this thread. I found it dormant 3 months ago when I first posted on page 1. This is page 10 ... lots more good stuff here than I ever would have dreamed!
Thanks,
Frank
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post #281 of 4798 Old 06-06-2008, 01:08 PM
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I built an LPDA two weekends ago following these plans: http://www.qsl.net/va3rr/hdtv/HDTV.htm

The guy has done some modelling of the design and it seems reasonably effective (for the size) though not terribly impressive. I had better results spacing the two booms apart about 3/4", maybe a little less. I'm not sure what the resulting impedance is but it's working better.

Comparing to an off-the-shelf, unamplified Silver Sensor, it beats it in one location in my house where it actually brings in a channel I couldn't get before (something like 8kW on channel 57 some 20 mi. away) but is worse or comparable in other areas of the house.

I added a air-choke and a ferrite choke similar to this: http://www.vk2zay.net/article.php/43

Out of curiosity I took apart the SS and found its internal design to be very similar, though it doesn't have any sort of choke or transformer inside.
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post #282 of 4798 Old 06-06-2008, 04:42 PM
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Heres one I found log periodic I tried this one not in PVC but in wood and didnt get too good results with it. It could always be the construction though. And heres a Yagi I tried that didnt work either, I used the rods from on old VHF antenna, may have been off a bit in dimensions.
But Im very glad to get the VHF this way, was watching tennis on Channel 6 with it and dont plan to go aereal until the news about Lousianna Public Broadcasting is know where theyll build a tower for Channel 25 KLTS at only 48KW radiating power,but so far everything is acceptable from the table top.

P.s the Log periodic is from mother earth news May/June 1985
LL
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post #283 of 4798 Old 06-06-2008, 05:32 PM
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Heres one I found log periodic I tried this one not in PVC but in wood and didnt get too good results with it.

Yep, I built that one in wood too, and pretty much all the Popular Electronics antennas published up to 1987. (MotherEarthNews plagerized that one from them, the Pop Elect one was about 1979-1981 IIRC.) It performed pretty mediocre in my attic, but Log Periodics are mostly about bandwidth and not gain. I have an old suburban type vhf/fm/uhf with a 30 inch boom in my collection that basically outperforms it. Its actually a fanscinating simple design, and I dont know who made it in the early 70's. From the measurements it follows all the rules. The uhf part of course is weak, but from 60 miles out, I get pretty much all vhf, high and low, almost snow free. Not bad for the boom length.

I like the old articles you have posted. Are most of them from old 1950s and 1940s Popular Mechanics ?? Ive some of them too.

@mclapp,
Yeah just like you, Ive found that most of the 8 bay bowties Ive built in the past performed maybe a hair better or a hair worse than the 4 bay versions. But, nowhere near the 2.5 to 3 db gain or something like it should have. I was pleased that I did get a very noticable gain on the DBGH over the single bay SBGH version.
It has to be in the phasing line between the two 4 bays. Have you tried straight phasing lines like on the CM4228 or the "V" straight phasing line like on the AntennaCraft U-8000 ?
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post #284 of 4798 Old 06-06-2008, 07:40 PM
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[quote=300ohm It has to be in the phasing line between the two 4 bays. Have you tried straight phasing lines like on the CM4228 or the "V" straight phasing line like on the AntennaCraft U-8000 ?[/QUOTE]

I use 450 ohm ladder line it seems to work the best with the limited testing I've done.

I tried a feed like the cm4228 but wasn't impressed, that style feed system should work good but something seems to be off with it.

The major problem is that your taking (2) 300 ohm antennas and combining them to a common feed point which cuts the feed point impedance in half, that turns into a mismatch which = loss.

I know that each half of the 8 bay is not 300 ohms at all frequencies but it's pretty close on most.

I've tried a few computer simulations of different feed set-ups but really haven't put much effort into it yet.

I'm concentrating on the 4 bays and when I think I've got all I can out of the 4 bay I'll work on a stacking arrangement either vertical or horizontal.
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post #285 of 4798 Old 06-06-2008, 08:35 PM
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tried a feed like the cm4228 but wasn't impressed, that style feed system should work good but something seems to be off with

Before you disassemble, try the AntennaCraft U-8000 "v" straight feed design using just equal straight wires. (Boy, I thought I was weird having open wire 300 ohm stuff, but even Ive never even heard of the 450 ohm ladder stuff, HAM radio I presume).

And just in case anybody is interested, the last 4 and 8 bay bowties I built were in the real bow-tie type design, in other words each section looked like a skinny heart. Copied from a Sony portable Uhf design that came with the set, about 7 inches long and 3 inches high. Didnt perform any better than a "whiskers type" design. At least I can scrap it and make a 8 and 3/4 inch whiskers design from it. Even though in my situation I need channels 6 and 12, Im very curious to see how channel 12 will perform with a 15 inch spacing reflector.
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post #286 of 4798 Old 06-06-2008, 09:29 PM
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Well I guess this is painfully obvious but its possible that working with the baluns then the twinlead maybe better for the equal splice, at least I forgot how to do it. Of course I knew I had good reception but had no way of seeing the dbs it was getting.
But I understand the CM is 8" and 9.5" or 10" works excellent on VHF; and it also does extremely well on anything UHF; in the air it does master the sky.
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post #287 of 4798 Old 06-07-2008, 08:43 AM
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Let me preface this by begging for forgiveness if this is a really stupid question, but you see I'm a total noob when it comes to antennas and have no real understanding of how they work (but I'm reading a lot and trying to understand all the great information provided here). Anway, here goes ...

I was reading with interest the thread about the 30" bowtie for VHF high reception, and it occurred to me that the 30" bowtie could easily be combined with the SBGH, thus covering the channel range needed after Feb. 2009. I assume the reflector screen would be 15" behind the driven elements.

I whipped up a quick drawing to show what I mean (see attached). Looks kinda like a flying bug. So the question: would this work? If not, could one of you very knowledgeable members please provide an explanation as to why it wouldn't work?
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post #288 of 4798 Old 06-07-2008, 06:51 PM
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Actually tblue01, I have already tried that with my DBGH. Oddly, I could get channel 6 better than a dipole, but channel 12 came in worse than rabbit ears. I suspect its the total length of the thing. I also tried attaching telescoping rabbit ears to it and experimented with many, many lengths and positions. No matter what I did, I couldnt get channel 12 to come in better than plain rabbit ears. Getting decent channel 6 didnt seem to be a problem.

Also I noticed when adjusting for the best position for channel 12, uhf reception suffered. This didnt happen for adjusting for channel 6.

What Im going to do is connect a small vhf antenna to the DBGH using a uhf/whf splitter as a coupler, as I have channels 6 and 12 going back to their old frequencies after February.


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Of course I knew I had good reception but had no way of seeing the dbs it was getting.

Neither do I, but 3db extra is the doubling of signal, which is obvious on weak channels.
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post #289 of 4798 Old 06-07-2008, 07:54 PM
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Nice thinking, I've seen stuff less logical than that actually work but this is not one of them.

Just for kicks I did computer model it.

The problem is that 30" bowtie actually works as a uhf antenna at some channels, because of this attaching it to the hoverman directly like that causes a big imbalance in the hoverman on those channels. Very similar to stacking to different antennas together the currents (signals) flowing through the wires oppose each other causing a net loss on 1 or both antennas. It would work ok at some channels but totally screw up others where the 30" bowtie is working as a uhf antenna.
The same holds true for the VHF-HI reception to a lesser extent. The Hoverman will have a slight negative effect on the 30" bowtie because of the close proximity of the wires to each other and it's very limited ability to work as a VHF-HI antenna.

Even if it did work a single VHF-HI bowtie wouldn't make much more than 3-5 db of net gain even with a reflector and a 4 bay with a large reflector spaced at 14-16" will do that and get UHF too.

300 ohm

I belive the reason why you could get the ch6 - hoverman combo to work without messing up the UHF is because at that frequency the to antennas don't interact. The ch6 length probably doesn't work as a UHF antenna which limits the interaction.
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post #290 of 4798 Old 06-07-2008, 08:40 PM
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300 ohm

I belive the reason why you could get the ch6 - hoverman combo to work without messing up the UHF is because at that frequency the to antennas don't interact. The ch6 length probably doesn't work as a UHF antenna which limits the interaction.

Yep, I was thinking that too. I does probably mean that the Hoverman-Dipole combo could work as a uhf/fm antenna, if anyone ever needed such a thing.
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post #291 of 4798 Old 06-08-2008, 08:11 PM
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Well Ive been assesing both antennas and running experiments. I managed to get the pipes installed by drilling through the reflector support and then bolted two pipes in the air. I got about a 40% increase all around at that height and was glad; but then the shoddy materials which was the Phillips RG6 pulled back through the wire and I kept getting no signal. So I guess I'll need a professional coax setup for cable with supports; I regretted it as I used to have miles of the old cable stuff out here but sold it for scrap wire.
But ultimately the 9.5" with bent cage is the best and sharpest and Ill just brainstorm some setup in a tree for the future in Febuary. Most of the digital channels repeat themselves and the areal setup gives me not much else to choose from out here; so the desktop miraculous as it is with the 9.5" is fine. but mostly its ironic that the store bought materials and baluns cause more trouble than the stuff that is handpicked from the garbage heap.
I'm still fascinated by the reflector, as with the Newtonian parabolic mirror much more signal can be concentrated into one area; I looked at the corner reflector I had posted earlier and even the layout for solar cookers from foil to concentrate the signal onto the elements like using a coffee can with coaxial on the end of an old satellite dish.
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post #292 of 4798 Old 06-09-2008, 05:40 PM
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Just finished my 4 bay bowtie without the reflector and D#$n ! what a difference!! from a UHF loop on a set of rabbit ears. I made the "v's" exactly 7" long with a 3.5" spacing.
I was able to picked up "ION" TV (65.1 ch) 30 miles away with the antenna leaning against the folding chair on th ground with a 4 story building dead in front of me!
Channel came in crystal clear with no drops(except for when the wind blew it over haha)
Antennaweb.org stated: I would need a medium directional ant with PREAMP to recieve this station...hahaha I did'nt Total cost: 2"x4ft .51 cents from Home depot,and 1 1/4 " screws $.98 cents,and washers $.98 cents....$3.71 with tax from Home Depot
Works like an $70.00 antenna here in Orlando,fl picking up Melbourne channel.Will put a pece of sheet metal for reflector on it soon & hopefully some pics to upload here as well.
Have'nt had this much fun since I made my first 10 mtr dipole antenna in 1995 when I became an Amateur Radio Operator
73's And thanks to all who submitted to my homework..hihi
Joe (St Cloud,fl)
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post #293 of 4798 Old 06-09-2008, 07:20 PM
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Quote:
Originally Posted by Joe23 View Post

Just finished my 4 bay bowtie without the reflector and D#$n ! what a difference!! from a UHF loop on a set of rabbit ears. I made the "v's" exactly 7" long with a 3.5" spacing.

Joe (St Cloud,fl)

First of all. WELCOME TO THE FORUM. I have had a lot of fun building many antennas which I call YouTubes, 4 bays, no reflector.
http://www.youtube.com/watch?v=EWQhlmJTMzw
Joe. I'm not sure what you mean by 3.5 spacing. Are the attachment points 3.5" apart?

Bob 61231
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post #294 of 4798 Old 06-09-2008, 07:37 PM
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Tombobiche glad to hear you got that antenna up in the air for a test. Too bad you had some technical difficulties with your coax, some of those factory crimp jobs are not too good.

How far away were the stations you were pulling in?

Have you ever checked tvfool.com to see what stations it predicts you should get?

I'd be interested to know what your actually getting and what your predicted to get, that's usually a good indication how well things are working.
I'm getting some stations that tvfool doesn't even list for my location with mine but with the hilly terrain around here the predictions could be easily skewed.
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post #295 of 4798 Old 06-09-2008, 09:58 PM
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Good Morning, the spacing is at the ends of the bowties or top of the "v" away From the 2x4 board.From tip to tip on each one.Was thinking of getting some sheet metal for A/C construction to use for the reflector;cardboard and foil would not work since it's going to be put outside.All of the wire I used was from very thin (cheap) clothes hangers.I realized the thick ones are not so easy to manipulate.taped some electrical tape over top the "cross-overs" and had a heavy-duty transformer(sylvania) from many years ago just sitting in my tool box.I rea
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post #296 of 4798 Old 06-10-2008, 05:33 AM
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Was thinking of getting some sheet metal for A/C construction to use for the reflector;cardboard and foil would not work since it's going to be put outside

Since its going outside, keep in mind the wind. Sheet metal makes a nice sail. Fencing works much better against the wind.
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post #297 of 4798 Old 06-10-2008, 06:24 AM
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Originally Posted by Joe23 View Post

Good Morning, the spacing is at the ends of the bowties or top of the "v" away From the 2x4 board.From tip to tip on each one.Was thinking of getting some sheet metal for A/C construction to use for the reflector;cardboard and foil would not work since it's going to be put outside.All of the wire I used was from very thin (cheap) clothes hangers.I realized the thick ones are not so easy to manipulate.taped some electrical tape over top the "cross-overs" and had a heavy-duty transformer(sylvania) from many years ago just sitting in my tool box.I rea

Joe23 welcome to the forum, as 300 ohm said if you're going to use it outside try to use wire fence or hardware cloth for the reflector. I'm not sure of the size you will need or the spacing since the Utube dimensions are very different from the dimensions I use on my 4 bays.

Both dimensions can make or break how the antenna will work or not work.

I would suggest a reflector minimum of 36" high by 24" wide and space it 4" - 5" behind the elements.

I don't know if the Utube version was designed to be used with a reflector but I'm sure someone has added one to thiers and maybe they would have a better suggestion on size and spacing.
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post #298 of 4798 Old 06-10-2008, 07:44 AM
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300ohm & mclapp, thanks for the feedback on the combo antenna idea. I had thought that VHF-HI was sufficiently distant (MHz wise) from UHF that there wouldn't be any crosstalk. I knew the Hoverman was only for UHF, but I didn't realize the 30" bowtie would also work for some of the UHF channels. Now I know.

Regarding the 4-bay bowtie with 15" reflector spacing, do you know what kind of gain one would expect down to channel 7? Come Feb. 2009 channel 7 (ABC) should be the lowest channel frequency in my area. Thanks again.
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post #299 of 4798 Old 06-10-2008, 10:00 AM
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Quote:
Originally Posted by tblue01 View Post

Regarding the 4-bay bowtie with 15" reflector spacing, do you know what kind of gain one would expect down to channel 7? Come Feb. 2009 channel 7 (ABC) should be the lowest channel frequency in my area. Thanks again.

The 15" reflector spacing used on the 9 1/2 or 10" bowtie design I posted on this forum will have about 5 dbd net gain on VHF-hi which is about the same as a small UHF-VHF combo antenna like a Radio Shack VU-75 or VU-90.

I had good luck with the original 5" spacing, but the 15" spacing just adds 2db net on certain VHF-hi channels over the 5" spacing due to a better impedence match. In my field tests it made very little difference on 7 & 8 but improved 9 on up.

I currently have 2 stations broadcasting in digital on channels 7 & 8 in my area and I receive them with better signal strength than the UHF station which is broadcasting from the same city about 40mi. away.

I have another one of that design that I installed for a friend and he's getting channels 7 & 8 @ 40mi. and ch's 11 and 13 @ 70mi. as well as UHF ch42 @ 40 and ch32 @ 65mi. It replaced a VU-90 which was only receiving ch 7 & 8 on a regular basis at that location.

The area where I live has alot of small hills so transmitter and receiver location means alot and UHF signals suffer the most so my results may not be typical.

It's by no means a serious VHF-hi antenna but it seems to work better than I would have thought in this area
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post #300 of 4798 Old 06-10-2008, 03:14 PM
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I looked at TV fool and in the air I only gain for Channel 12 CBS and 45, which 45 repeats itself on 19.2 MYTV which shows Hawaii 5.0, Rockford Files, Magnum PI, Mission Impossible, Seinfeld, Star Trek, Heat of the Night, ultimately I guess I have to capitulate and take whats on the ground. But height makes a huge difference and in the air I got about 40% stronger; but some of the previous posts for YouTube models show a hanging hook which is invaluable too, as rotation just a few feet above the air can make a collosal difference.
But I did test the 7" against the 9.5" indoors and found that the 7" failed to get Channels 6, 33 and others nearly as good, and then on analogue 24 no question, even my worst version of the 9.5" brought in a crystal clear image upon height and rotation indoors above the blurrier 7". But Im sure a double stacked Hoverman would have covered it nicely.
Still Im thinking the 9.5" is best all around with 5" spacing and bent cage reflector, but tests on the Hoverman and 7" with a reflector may show in the higher UHF Channels theres improvement, but so far with the range and tuning of the 9.5' Im gonna stay with it.
Well heres some pics of how I drilled the holes to get the pipe installed; at this weight I'd recommend guy wires or a mast mount to the eaves and overhang. And heres a makeshift test on the 7" for which Im watching analogue in lighting storms. I did find that those 8 cent washers at Home Depot do much better at solidyfyng the join between the element and the phase line.
LL
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LL
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