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Discussion Starter #1
The UHF Loop is a very small, simple, easy to build, and place, bi-directional antenna.

Bi-directional, means it receives best from 2 directions. It receives from the front and back of the loop.

The UHF Loop is quite wide-band. Meaning it can receive many channels fairly well.

But the UHF Loop has to be pointed / or adjusted to get the best result.

(but the advantage is that UHF Loops are so simple and cheap and small ... that you could build and place and point several of them in different places and directions to give you more local or neaby channels coming from different transmitters)

Because the UHF Loop is SO very simple, and because it is bi-directional, and wide band, so cheap and easy to build, and so small (relatively) ... it is great antenna for DIY's - do-it-yourselfers - to build and to do tests experiments with.

I think the UHF Loop has great possibilites to help bring and introduce and promote OTA reception to MANY easily and quickly.

And the UHF Loop may be able to solve many "one off" problems with local or nearby reception.

This Thread is created to:

- introduce UHF loops widely to the masses - to encourage OTA
- build UHF loops
- share UHF loops designs and OTA results
- use UHF loops to solve "one off" problems in OTA receptions systems.
( i.e. to get those "few extra channels", simply, that you can't get well from your existing setup ... because you've got to point in a different direction, for other reasons or problems).
- to experiment with variations on the UHF loop
- try out multiple UHF loop "systems"
(for example to point at multiple transmitters in different directions)
- experiment with "additions" to the simple UHF loop to make improvements or solve pesky reception problems. (ex. with screens, reflectors etc. )
- experiment with the use of UHF loops to receive more than just UHF
(because the UHF loop is, by it's nature, broadband, you may find it can also receive some VHF High ch 7-13 ... or even some VHF Low. I have actually received a strong local analog VHF ch 6 pretty well, testing with one UHF loop.)
- experiment with the dimensions, size, diameter, material etc. of the loop.
- mounting, placement etc.
- screens, reflectors etc.
- anything else you can dream up - using a UHF loop.

Have fun.

I'll be posting more shortly ... on my UHF Loop endeavouors.

"Go for a LOOP"
 

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Discussion Starter #3
Here's a picture of my simple test UHF loop setup. (pretty simple eh?)

It's a UHF Loop from an old portable analog TV we had from way back.

It's just a circular steel ring, about 7 3/4 inches in diameter, screwed down to a piece of 2/4 wood, with old balun / matching transformer attached.

A long piece of coax (not shown) attaches it to the input at the back of the TV, and you're free to move it around and point it around in the room.

This original loop has "ball joints" so you can rotate it around (but you don't need those using it like this ... because you move the unit around with a long piece of coax going to the TV.) This loop was was originally intended to connect directly to the 300 ohm UHF terminals at the back of a portable TV, and sit right behind the portable TV.





In Kingston Ontario,

Analog reception with this UHF loop, from inside 2nd floor room:
(aiming UHF loop manually, for best reception)

ANALOG

VHF LO analog
2 Global (north east from Bancroft)- nothing - (far and VHF LO)
6 CTV (west from Deseronto) - fairly good reception - a little weak and snowy, no ghost

VHF HI analog
11 CKWS - CBC local - clear and strong (strong local channel)

UHF analog
15 "CBLFT13" (CBC Fr.) Clear w/some static - no ghost
32 "CBLFT14" (CBC Fr.) Clear and strong - no ghost
38 CICO TV-38 (TVO) Clear w/minor static, no ghost, a little wavy at times, sound a little raspy, minor transparent line down screen.
53 CICO TV-53 (TVO) Clear picture, moderate static, no ghost, o.k.


DIGITAL ?

(none locally in Kingston yet ...)
I have not gotten around to trying connect the UHF loop to the digital converter box, and point towards the U.S. and try ... but that's the next test.

Watertown N.Y. is around 45 miles away (WPBS 16-1,2,3 , CBS WWNY 7-1, 2)
[ I get these easily with other outdoor antennas on tower ]
[ Long ago, we used to get WPBS analog with the loop, inside the room, 2nd floor]

Thoughts:
IF you stuck a couple of these simple UHF LOOPS outside, high up, and pointed them correctly towards the different transmitters ... I think there would be better results - analog - better picture and sound quality than what I am getting testing from inside.)

(THIS BODES WELL for the UHF LOOP, for simple "nearby" local or suburban Digital reception ... alot of that is going in the VHF-HI and UHF direction. And because with digital, if you get a good enough signal ... you've got good picture and sound - no ghosts or snow or raspy sound with digital - compared to analog).

SIDE NOTES:
I've also been experimenting with screens and reflectors placed around the loop, to see if picture or sound show any minor improvement. Or if interference or ghosting can be reduced. Or if reflector at the back can increase gain and improve analog picture or sound.

The UHF LOOP is also showing advantages over a 21 inch, omni-directional, amplified and FM Trapped, UFO antenna out high on the tower. There's a lot more ghosting and interference and wavy picture and rolling picture from the that omni-directional UFO antenna on some channels. Some analog channels are unwatchable from the omni UFO. Even with better placement and high up outdoors. It must be picking up reflections from all directions ... and overloading the pre-amp on some channels esp ch 32 CBLFT only 3.6 miles away and very strong. Not sure how all this will translate after transition to digital.
 

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Discussion Starter #4
300ohm

Excellent. Thanks.

That internet link and the information given there ... is pointing everyone quickly in the right direction ... with the LOOPS.

Now time for me get out and "go for a loop" myself ... catch ya later ...
 

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OK, my age is realy showing :p

Back a few years ago, when UHF TV stations first surfaced. Some lucky guy made a loop out of 8" of wire, then bent the tips so they could mount onto the two screw terminals on the back panel of a tv set. He made his millions through radio shack, I believe his name was Tandy. If I recall the story correctly, he was 8 years old at that time. At that time I had lots of hair, but no whiskers. Soon after when UHF became more popular and then tv manufacturers included a free UHF loop with each new TV set, oooh wow! That seemed like a bonus at that time. I think I still have a few still in the original RS or TRS bags somewhere in my shop :D Now I have a full beard and very little hair and a bigger antenna.

Try mounting that loop & balun on your tower with a rotor and a preamp, I'll bet you'd be quite surprised at the results.
 

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Isn't the stealth hawk similar to the loop except it has angles?
Yup! A diamond shaped loop with downward rabbit ears.:p

Actually we did some experimental trials with oct/hex shapes and with a full loop, but in the end, the lengths of the wiresections and the angle of the bends play a big part in performance and directional coverage.

A simple round loop at the correct diameter will cover the full 14-69 UHF range, but it is bi-directional [with a reflector it becomes directional with slightly more gain] and the gain peaks at the mid UHF range and is much lower on both ends of the UHF range. All of our Stealth Hawk experimental mixes and matches done through this forum proved to level out the gain somewhat across the entire 14-51UHF range and also acheived some VHF benefits. Throughout our experiences with the Stealth Hawk, we've learned to never say never!;) The quest for the perfect OTA TV antenna continues.
 

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Discussion Starter #10
Digital ?

Digital reception, with my UHF loop, photo above, from Kingston, Ontario.
Antenna inside a bedroom, 2nd floor of house, through one brick wall.

Weather: Clear and calm, no precipitation, no snow or rain.

Time: Round 8 PM - Saturday Night

About 35 ft of Coax to the receiver (Digital Convertor Box).

Digital Reception Results:

7-1 (RF 7) WWNY-HD (CBS) Watertown NY. 30% - 35%
7-2 (RF 7) WNYF-SD (FOX) same ... 30%-35%
(stable and totally watchable. minor pixellation but rare. no sound issues)


16-1 WPBS-1 (PBS) Watertown NY. 40%-48%
16-2 WPBS-2 (PBS) same.
16-3 WPBS-HD (PBS) same.
(stable and totally watchable. no pixellation seen. no sound issues.)

50-1 WWTI - (ABC) nope, nothing.
50-2 nope, nothing.
(usually my next best one)

WWNY and WPBS transmitters are about 45 miles away from me (!) in Watertown N.Y.

I'm probably close to LOS from the second floor bedroom.
I'd say height is 20 ft.

Careful aiming and placement of the loop in the room was needed to get best results. But once placed - stable reception.

I tried in center of the window, facing transmitter, but that did not work.
Practically no signal.

I suspect something in the glass or the aluminum window frame and aluminum flashing just outside messes up the signal.

Best results were straight thru the brick wall, side of house facing the transmitter, where there is likely no metal. (Brick house with wood framing).

You've got to experiment with placement and direction.

You may get signal where you least expect it.

Hook up a length of coax and move around the room, or to different rooms and see what you get.

I think reception may break down abit in bad weather with this simple antenna.

But 45 miles, with that simple little antenna - and those results. I'm surprised.


For those of you in Kingston and surrounding area ...

Superbowl ?

The Superbowl is on next Sunday, I think, and I hear it's on FOX.

This "small" UHF Loop is not really designed to catch RF 7, VHF Hi - but it does for me.

Depending on your location / situation / conditions ...
Maybe you can catch the Superbowl easily, in SD, OTA, Standard Definition on 7-2 (WWNY's SD re-broadcast of WNYF-(LP) FOX, low power transmitter).... minus the Canadian Sim-subs, and with the original U.S. commercials.

Better antennas placed outdoors - no problem - and you may then have other options and other channels to receive FOX from Kingston and area ... possibly in HD.

(ex WNYF-LP Watertown NY directly. Then one from Syracuse NY FOX 68-1, 68-2 - harder to get - but I get it usually with long UHF YAGI and good pre-amp high up on 40 ft tower. There's also FOX out of Rochester ... those West of Kingston over in Belleville area might have a better shot at Rochester NY - across Lake Ontario.)

... and, of course, WPBS OTA is awesome !
 

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Discussion Starter #11
SBL's - Shorted Bowtie Loops

Thanks, 300ohm and holl_ands,

Awesome. Now we're shaking out some good stuff.

So ya, according to specs and plots shown,

The SBL's - Shorted Bowtie Loops - are a little bit bigger, look like they have about 1db more gain than a simple loop, and lower SWR.

Looks like their gain falls off near the top of the UHF range ?
Is that correct?

And work better with larger diameter material - just like the loop.
( 1/4 or 5/16 or 3/8 inch copper tube ? - oh ya! ... get the plumbing and soldering tools out)

But ya - look good - and still very simple - and not too big.

And the elements inside the loop can also add strength / physical stability.

They've got a nice bi-directional pattern - just like the simple loop.

Very useful ... in the OTA toolkit.

Shorted Bowtie Loop deserves it's own Thread ... and member experimentation.

ANY Photos OF AN SBL ? Connected and in use ?
 

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Looks like their gain falls off near the top of the UHF range ?
Is that correct?
Yes, but it was designed that way. The gain falls off after the maximum gain is achieved, and we wanted the max gain near the end of the new uhf range, channel 51. But the SBL has an incredible bandwidth, much more than a loop or bowtie. The gain charts only show down to 470 mhz. The gain and SWR continue to be about the same down to about 300 mhz.
The SBL loop would have been a great indoor antenna for the original channel 14 to 83 uhf range. Trouble is, it was discover too late.
If you want coverage to channel 69, just make the SBL smaller.:)

ANY Photos OF AN SBL ? Connected and in use ?
Yes, theres at least one on this forum. The problem is finding it again, heh.
 

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Vorg built X447, a Six-Spoke Shorted-Bowtie-Loop, here's the photo:
http://www.digitalhome.ca/forum/showthread.php?p=992047
Which was analyzed here:
http://www.digitalhome.ca/forum/showthread.php?p=982724

Post #557+fol. has analysis of an EIGHT-Spoke SBL:
http://www.digitalhome.ca/forum/showthread.php?p=989387

If you poke around, you'll also find an SBL with the apex offset to the rear
and a couple of reflector arrangements....

Several SBL configurations are analyzed on my LOOPS webpage:
http://imageevent.com/holl_ands/loops
You will ALSO find analyses which finds\ the OPTIMUM Loop sizes for the
OLD and NEW UHF Bands.
 

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Discussion Starter #14
Photo of an SBL built by Vorg

Found a photo of a constructed SBL - shorted bowtie loop - built by Vorg.



Can be found in Vorg's Album.
 

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Discussion Starter #15
Thanks holl_ands,

I saw your post just after I added the image of Vorg's SBL.

In any case, last night, I made an attempt to build Holl_and's "UHF/VHF hi bowtie in loop" based on the image / sketch / design from his website:



I used whatever I had handy at home. I built this:



But I realize now, I may have gotten something fundamentally wrong. I have the feed point shorted out with a solid 1/4 inch threaded rod (!).

[hard to tell from the sketch, but the feed point is supposed to be open, correct?]

Anyway, here's a description of what I built:

(I built it from memory ...what I remembered from the drawing I saw last night.)

22 inch diameter loop (AL rim from a 26 ? inch mtn bike wheel - had broken spokes so I just cut them out w/bolt cutters)

length of 1/4 in threaded rod - across center of loop.

whiskers: 3/16 steel rod - salvaged previously from old discarded lawn "signs" (shhh)

(whiskers cut to 18 inch, bent 37 deg, yeilding about 8 1/2 inch long whisker to fit inside hoop)

1/4 in hardware, nuts, washers ... # 6 hardware, small bolts & nuts.

clips made from steel pipe strap

I think my feed gap is wrong - too big - about 2-3/4 inch now.


Anyway, I hooked it up, and even with the feed gap shorted out, and the wide feed gap, it still receives fairly well.

Even as is, with major errors(?), it gives a clearer picture on some analogs, rejects ghosts better, and picks up the digitals with better signal strength when placed in the right spot, and aimed properly.

I find the aiming is more sensitive. If you go off 4 or 5 degrees on the aim, you immediately see a loss. It's more "finicky" to aim. That may be a good thing ... it's beamwidth must smaller than a simple loop.

Anyway, digitals from Watertown NY showed a 5% - 10% increase over the simple 7-3/4 inch loop from my last tests.

Digitals around 48% this morning with this "bowtie in loop" thing.

I may need to make adjustments / corrections and re-try.

I think a proper, quality build, with good materials - can yeild excellent results on this antenna design.

( No rod across feedpoint ... correct? )
( Feed gap looks like should be around 1 inch? )
( I may have the whiskers angle wrong also. It's 37 deg from the center line, that's 74 deg, whisker to whisker. Correct? )
 

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but the feed point is supposed to be open, correct?
Yes, when you see a wire with the red/pink ball on it in a model picture, thats the feed point open space.

The feedpoint gap on it is supposed to be 3/4" (.75 inches)

Just cut it to that in the middle and giver a go. :)
 

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Discussion Starter #17
Re: Holl_ands' Bowtie in Loop - test results after proper build adjustments

Made the adjustments.

Cut the feed gap, adjusted it closer by spinning the nuts inward.
Put a piece of vinyl tube tip to tip to try and keep threaded rod lined up.

Re-bent the whiskers to the correct angle 74 deg. whisker to whisker.
(37 deg. whisker to center).

Yes ... much better results. Same test setup and same test location.
35 ft coax to the tv. inside 2nd floor room 20 ft up, thru brick wall.

Analog:
Yes, Kingston local analogs little bit better. Little bit better picture quality, less static and ghosts on almost all channels - if aimed and placed carefully and correctly. Pretty clear analog picture now, overall.
(better potential for analog signal quality over a simple smaller UHF loop.)

Digital:
7-1 -2 (rf 7 ) WWNY CBS/Fox near 70% now. (wow, 30% increase from simple loop!)

16 -1 -2 -3 (rf 41 UHF) WPBS - 35% best I could get. (? small drop compared to simple loop ? why? )

Aiming is a little bit more demanding than a simple loop - but not too difficult.
It became a little easier to aim, after I cut out the shorted feed gap.
Still more directional than the simple loop. Might be a good thing.

I think the small drop in UHF (and no major increase - like the VHF hi 7) could be due to material being used and build method / build quality.

A 1/4 in steel threaded rod is not going to perform well at UHF. Also because this is a nuts and bolts build. Nuts and bolts connections probably have spot conductivity. (and UHF, higher frequencies, will have smaller "skin depth" ... so conduction is happening closer to the outside surface of the conductors.)

I think much better results on UHF if the Bowtie in Loop is built with proper size round copper tube or rod, properly fitted and butted, and soldered all around. Or with Aluminum rod or tube - same deal.

Quality of build and materials more important at higher UHF frequencies.
Makes sense.

Interesting ... performs really well at RF 7 - bottom of VHF hi.
[ Perhaps Kingston is a good location for testing - we have a VHF hi, rf 7, 45 miles away, close to LOS ]

This antenna - better yet with a good build.
This antenna - better yet outdoors, higher up - I'm sure.

I have an idea how to build this antenna more simply.
I'll try to make a sketch and post.
 

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Discussion Starter #20
Holl_ands ...

Rigidity / straightness of the threaded rod?

Well for now I just cut a short piece of vinyl tube (flexible) I had handy and slipped it between the ends. That only worked so so ... but good enough for tests.

One idea was to get an extended (long) nylon nut. That way you could maintain some pull tension in the threaded rod, and that'd keep it straight too.

Or use something more rigid than vinyl tube, like short piece of hard plastic tube.

[ plastic at feed gap probably has effects - I'm guessing - maybe not the best idea for a real build ]

But anyway - this is a hack / quick build for simple tests.


EVERYONE:

I have a couple better ideas for a "REAL" build:

- one idea simple, more rigid, with straight rod (working on sketch - will post soon).

-One idea for copper tube - obvious, but I'll give some ideas HOW to build it.

BOWTIE IN LOOP

Possible Construction Method w/ Half inch Copper Tube and Fittings:

1/2 inch copper tube? - probably a great performing antenna.

Construction Idea:
- 2 half loops, bent of 1/2" copper, join into a full loop w/ T's
- possibly use a bike wheel rim as the bender/guide, since it is near the correct size (leave the spokes in, it's a lot stronger that way as a bender or guide).
- T's at feed gap. Then 45deg "street elbow" fittings into this T to give near the 37 deg whisker to center angle required for the whiskers.

Bend constructed fitting at feed gap a little to get required angle.
- at feed gap joint, first solder the 2x 45deg street elbow into the T.
- Now hold T in vice w/one 5/8 (approx) round short piece of bar.
(outside diameter of 1/2 copper tube is approx 5/8 - this is also the inside diameter (approx) of the fitting(!)
- Take another two longish 5/8 round bar/axle rod, use them as levers/benders, place in ends of "45 street elbows" and give it a small bend inwards to get the correct angle for the whiskers. (you've only gotta add an 8 deg inwards bend to each street elbow. 45 deg - 8 deg = 37 deg.) Should be possible without kinking or "offending" the fitting too much - but gotta experiment and try first. The tight fitting 5/8 round bar should also maintain the roundness of the fitting, when you go to give it a bend - so when you go to insert the whisker tube to solder it, it still goes in allright. (get the idea?)

(what if it were left at 45 degrees? big change in performance? Could it be designed for 45 deg whiskers? no bending required then. Or do they make other odd angle fittings ? probably harder to find and get. more expensive. any plumbers out there?)

Solder all the parts together.

Solder 2 small copper tabs w/small hole at one side of the feed gap to attach the balun. These can be made by cutting and flattening a short piece of the 1/2 copper tube material and making the tabs.

( Theory: The way you make the connection from the antenna's feed point to join to the balun's 300 ohm wire, is, I think, important. You're making the transition from antenna to transmission line here. More on this later. But briefly, you want to try and maintain the proper characteristic impeadance here - keep it "matched" all through this transition - best you can. More ideas on this later ... but this subject deserves a Thread of it's own. You'll reduce losses, going from the antenna to the transmission line this way.)
 
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