WSYRTV9's First Gen. SBGH Build Plans

[WSYRTV9]

I stumbled across this site a few weeks ago and was intrigued enough by the data to try building a SBGH. The performance astonished me: I live in a valley where off-air reception is generally horrible, but this antenna pulls in every DTV station in the Syracuse area without a problem.

As it happens, I'm an engineer for a group of television stations in upstate New York... and write a feature for the Syracuse station's web site on DTV issues. This antenna so impressed me that I've been writing up a "do it yourself" version that uses PVC pipe and fittings -- no fasteners, and it makes the elements essentially self-forming. It looks like this:



Thanks for all of the time and effort to create such a useful device, for for the generosity to share it freely!

http://community.9wsyr.com/blogs/plu...7/3046816.aspx

-- Jeff

[300ohm]

Very nice workmanship and an interesting design WSYRTV9. I like seeing others ideas on the element spacing and durability issues.


A couple of constructive notes. You could use 1 X 1 or 1 X 2 mesh to reduce wind loading. And since the antenna is finished, you could very easily cut that 20mm vertical gap in the middle. According to Autofils graph, that would give you another 1 db in gain for channels 28-42. And if anyone is thinking of gluing the pvc, I would suggest using Plumbers Goop or Locktite Marine Adhesive and Sealant instead of plain pvc cement. It gives a much longer working time which is very needed for proper alignment. I could also see designing a pvc roof mount that would integrate with that antenna at the open tees at the bottom.

Technically, nylon ties are fasteners, heh. Oh, and theres a free downloadable program that reduces the filesize of pictures posted on the web without reducing the quality callled PIXresizer.

[WSYRTV9]

Thanks for the feedback!

That's very true about the 1x1 or 1x2 mesh... it didn't occur to me, mainly because I didn't find anything larger than 1/2", and I based the spec on material that was readily available.

I'll have to try cutting the gap... it would be quite easy once the screen is attached. I had originally intended to omit that detail, depending on the screen to add stability to the frame (to keep it from racking).

Indeed, the corner tees form a dual role: they figure into several mounting options, and also provide a drain so that water doesn't accumulate inside and freeze.

I'll have to look into these other adhesives... I didn't have trouble getting things aligned properly, so long as I knew what I was aiming for before starting. Having a template to line things up against really helps, since it removes the need to make quantitative measurements.

"Technically, nylon ties are fasteners, heh." I'm smiling: you got me there. What I meant was, screws and other stuff that requires more machining to the frame.

"Oh, and theres a free downloadable program that reduces the filesize of pictures posted on the web without reducing the quality callled PIXresizer." Thank you very much for that: I'll have to find that, as I've been frustrated with resizing things in Photo Editor.

Stampeder also gave me some very helpful pointers last night, and I'll incorporate them and much of this into a revision of the instructions PDF, hopefully later this week, "real" work allowing(!).

Regards,

Jeff

[300ohm]

That's very true about the 1x1 or 1x2 mesh... it didn't occur to me, mainly because I didn't find anything larger than 1/2", and I based the spec on material that was readily available.

Yeah, my local Home Depot also only carries 1/2 in mesh tops too, the rest is 2 by 4 inch fencing on up. The local Lowes does have 1 X 2 inch fencing. The best bet is local mom and pop hardware stores for short lengths.

I'll have to try cutting the gap... it would be quite easy once the screen is attached. I had originally intended to omit that detail, depending on the screen to add stability to the frame (to keep it from racking).

I can see that if not gluing. Nylon ties across the gap could maybe compensate for that. After all, a 1db gain may be important in some cases.

I'll have to look into these other adhesives... I didn't have trouble getting things aligned properly, so long as I knew what I was aiming for before starting. Having a template to line things up against really helps, since it removes the need to make quantitative measurements.

Definately, templates and jigs make the construction easy. On the Plumbers Goop, I dont follow the directions on the package. Package says let apply to both sides and wait 10 minutes for an instant fit. I apply a dab (for antenna construction only, not plumbing) to one side and insert immediately, giving the 10 to 15 minutes of adjustment time.
On the experimenting with the stuff, Ive been doing that for over a year now for a computer water block. I used a piece of copper to plexiglass with the glue and subjected it to boiling water for two hours, dunked in my goldfish pond for 3 months, and left out for the winter. It is still holding very fast, and I think the bond is very leak proof. Ironically, the dual core system I designed and made the water block for is running cool as a cucumber on the stock Intel cooling.
And oh yeah, its also great for repairing shoes, probably the best glue, leather or rubber.

"Oh, and theres a free downloadable program that reduces the filesize of pictures posted on the web without reducing the quality callled PIXresizer." Thank you very much for that: I'll have to find that, as I've been frustrated with resizing things in Photo Editor.

Download link : http://www.download.com/PIXresizer/3...-10607499.html

Youll love the simplicity. Good luck on your article.

[WSYRTV9]

Originally Posted by 300ohm

Nylon ties across the gap could maybe compensate for that. After all, a 1db gain may be important in some cases.

As it happens, I was able to just snip out the gap... having the hardware cloth already attached made it quite easy, and by snipping out the insides of two 1/2" rows of squares, it wound up being almost exactly 20mm wide.

Originally Posted by 300ohm

Good luck on your article.

Thanks -- I sent Stampeder a draft of the new first page with the proper attribution and licensing information this morning for him to take a look at.

For what it's worth, I got wondering how easily my PVC version SBGH could be adapted to make it a DBGH... it turns out that if you replace the two inner tees on the top of one unit with crosses, and build the second unit as a continuation of the first, you wind up with five inches separating the sets of elements -- which is exactly what's shown on the design drawing. As they say, never merely admit to luck... rely on it! One of these days I'll wander over to Home Depot and raid their plumbing department and give it a shot. Already the're wondering why I've blown through over 100 tees, but only nine sections of pipe!

By the way, thanks for steering me toward PIXresizer... I found it fairly easily this morning, and it's much easier than what I was doing!

-- Jeff

[300ohm]

Already the're wondering why I've blown through over 100 tees, but only nine sections of pipe!

By the way, thanks for steering me toward PIXresizer... I found it fairly easily this morning, and it's much easier than what I was doing!

-- Jeff

On the bright side, buying a hundred tees at a time is much cheaper.


Yeah. It pretty hard to get much easier than pixresizer. The quality of the image, depending on the size you choose for any given situation, is excellent for such a simple program. I can take a 3mb image down to 48 kb and still retain the main essance. It helps the dialup people like me.

As it happens, I was able to just snip out the gap... having the hardware cloth already attached made it quite easy, and by snipping out the insides of two 1/2" rows of squares, it wound up being almost exactly 20mm wide.

Definately doing it after its all finished is much much easier. And did you notice an improvement in channels 28-43, granted that its going to be a small change in most cases ?

[tvmonkey]

@ WSYRTV9,

Thanks for posting the detailed instructions. I am currently using a Terk TV5 low profile antenna. It work ok for some channels, but cant pick up most channels 100% of the time. Its also an amplified antenna.

QUESTIONS:

1. Are the #8 copper wire sections cut or do you route them thru the holes without cutting them? Seems like it would be hard, but if you dont do this how do you keep the ends of the rods touching inside of the pipes?

2. I have (2) HDTVs in my house. Can I use a splitter to feed both TVs from this antenna?

3. Does this have to be mounted on a roof?

4. What are the cutouts that people are referring to on the mesh?

[300ohm]

2. I have (2) HDTVs in my house. Can I use a splitter to feed both TVs from this antenna?

3. Does this have to be mounted on a roof?

4. What are the cutouts that people are referring to on the mesh?

Ill let WSYRTV9 answer the first one.

2. Yes, if your signal is strong enough. Generally there is about a 3db loss with most splitters.

3. Youll get better results with all antennae mounted outside than you would in the attic.

4. Cutting that simple 20mm vertical slot in the screen on the SBGH will get you .5 to 1db more gain (6%). Since its easy after the antenna is finished, I would go for it. Ill attach a picture of the graph:

[tvmonkey]

@300ohm,

Thanks for the reply. How do you think the SBGH would compare with the Terk TV5 that I have right now?
Here are the specs:
http://www.amazon.com/Terk-Low-Profi.../dp/B000069106

Also, the 20mm vertical cutout you are referring to, where is this located on the SBGH?

[300ohm]

The 20mm cutout split is right down the middle, from top to bottom. So in essence youre left with equal separate right and left reflector screens. Its easy to do once the antenna is finished, but I would certainly build the antenna initially as a full screen, and then cut.


The Terk TV5 doesnt have much in the way of an element. With the SBGH, youll certainly catch a lot more available signal. Where are you planning to mount it ?

If that amplifier in the Terk TV5 is any good at all, and with fairly low noise, you may be able to use it, with modifications, on the SBGH. Basically what you would do is take the Terk TV5 apart, remove the existing "diamond" elements, connect a length of 300 ohm twinlead to the points the "diamond" elements were connected to and the other end of the twinlead to the SBGH. The connection to your tv would remain the same.

But thats a big if, as most amps in indoor antennas arent that good to begin with.

[tvmonkey]

@300ohm,

Thanks for the info about the cutout. I plan on mounting this outside, maybe on top of my shed. Does it matter if its pointed on angled a certain way? Can it be horizontal or vertical? Once its mounted outside, I'm going to run a cable to the house and split it to my TVs. Before I set anything in stone though, I'm going to hook it directly to my main HDTV to see how the SBGH compares to the Terk TV5.

[WSYRTV9]

1. Are the #8 copper wire sections cut or do you route them thru the holes without cutting them? Seems like it would be hard, but if you dont do this how do you keep the ends of the rods touching inside of the pipes?

Each of the two elements are fashioned from a single five-foot piece of #8 copper wire, and you actually form the bends as you assemble the supports in place. Essentially, you start in the middle (at the feed points) and work outward. As a practical matter, this assembly method means that so long as you get the pipe sections cut to the correct length and aimed in the right direction, the elements wind up having the correct proportions. Also, having a support at every bend means that the element is going to keep its shape, even if you have heavy icing (or birds)...

The PDF instructions have fairly explicit step-by-step instructions with lots of photos that should make things clearer. Also, you can download a PDF drawing to make a full-size template... you'll need to take it to a place like Kinkos or a blueprint shop that can print it full size.

All of the pertinent downloads are available at my station's blog page.

One other note... I've made several revisions to the assembly instruction PDF which should have been posted on Friday... but the person who needs to upload the file to the server was sick. It should be available tomorrow (Monday).

Thanks,

-- Jeff

[WSYRTV9]

Yesterday I ordered a fairly new model Blonder-Tongue UHF preamp, their model #5019. It's 300 ohms in, 75 ohms out, and looks like I could easily build it right onto the SBGH. I'll be interested to see how this works out: not just for the sake of the preamp itself, but on the theory that having the amp's input impedance match the antenna might minimize SWR-related issues. We'll see.

The carton should arrive next week... can't wait!

-- Jeff

[tvlurker]

l Blonder-Tongue UHF preamp, their model #5019.

The specs don't look as good as the Channel Master preamps (2.2dB NF on UHF for the CM 0264 model, vs 3.3 or 3.5 for the BT.) The 5019 doesn't show any specs for total power handling. My 0264 seems to be fairly immune to xmod so far, and we have 14 local analog stations here in Ottawa.

Let us know how the impedance matching goes.
The CM 300 ohm input models come with 'no strip' piercing washers on the 300 ohm input connections, so you don't even have to disturb the geometry of the twin lead to connect it to the preamp -- just slide the twin lead under the terminals, and tighten them until the piercing washers make contact with the conductors. Of course, this just preserves the 300 ohm impedance. It will be interesting to see what kind of improvements you can make by altering the input impedance of the preamp -- if you can get to improve the net gain of the SBGH with the BT preamp by more than a dB or two, then it should be better than the CM preamp.

TVl

[300ohm]

If this antenna is installed outside, I would use 1" pvc and a reflector made of aluminum rod or tube.

The balun has to pass through the ID of the 3/4" pipe holding the two tee's together.

I built my DBGH with 1" inch sch 40 pvc, except for the feed line connection between the two bays which I figured only needed 1/2 inch. (See pictures 2 pages back) I think youre right, it should have been 3/4 inch to fit most outdoor baluns inside. (An indoor type would work though)

On second thought, since I have channels 6 and 12 reverting to their old assignments in February its a mute point for me. Im going to have to hook up a vhf antenna to it, and Ill be using a 300 ohm channel master vhf/uhf splitter in reverse as a combiner for the lowest loss, then the balun connected to it.

if you can get to improve the net gain of the SBGH with the BT preamp by more than a dB or two, then it should be better than the CM preamp.

Im confused, dont you like your CM 0264 ? I was considering getting it.