I'm gonna be building a DGBH soon, and I'm wondering if anybody has made a side by side, rather than vertically stacked configuration, and just wonder how it worked out for you.

Thanks!

wondering if anybody has made a side by side, rather than vertically stacked configuration

Nobody has made an outdoor version with pictures, yet. So youre welcome to be the first.

But the vertical stack does have its advantages, check out hdprimer.com.
The AVS forum antenna forum also had this practical outlook:
--------------------------------------------------------------------------------------------------
This is very useful summary of stacking describing the result beamwidth with horizontal and vertical stacking. A couple of points probably need a clarification. In either case the gain from combining two independent antennas will be 3 dB minus the loss in the combining circuit so the gain in not generally lower in horizontal stacking. The need for the antennas to not be coupled and therefore independent gives rise to the required minimum spacing. In general the higher the antenna gain the larger the required spacing requirement. For very narrowband, high gain yagis, amateur radio operators use a rule of thumb of half the boom length. Broadband TV antennas have less gain for a given boom length so they can be spaced somewhat closer. Horizontal and vertical stacking distance for yagis will be larger than half a wavelength and the plane with the narrowest beamwidth will need the largest spacing. For either plane it will come out less than half the boom length for TV antennas.
John


Quote:
Originally Posted by PCTools
VERTICAL STACKING

Stacking two identical antennas on a common vertical mast significantly narrows the vertical beam-width angle. That is, vertically stacked antennas more effectively reject those interfering signals arriving from above or below their horizontal plane than does a single antenna. It’s as though they were looking through a horizontal venetian blind. Because there’s nothing mounted to the side of either antenna, their side-to-side vision is virtually uneffected. In the process, gain increases about 2.5 dB over that of a single antenna.

Vertical stacking improves both gain and vertical directivity. This helps reduce airplane flutter and attendant picture roll, and certain types of ground noise and ground reflections.

The basic principle of stacked antennas involves the difference in the time of arrival, and therefore the phase, of signals intercepted by the antenna combination. If a pair of identical Yagi antennas are mounted one above the other, a wavelength apart, on a common vertical mast and are oriented identically (pointed) toward the signal source, any TV signals traveling horizontally and arriving from any direction will be intercepted simultaneously by both antennas.

Because the antennas are identical, the generated signal voltages arriving at the output terminals shared by the antennas will be in phase, causing them to add directly. Theoretically, there should be a 3 dB increase (double) in signal power over that of a single antenna, but, because of losses in the coupler and cable, the actual gain increase will be somewhat less than 3 dB.

An important point to remember is that, regardless of the azimuth angle between the antenna orientation and the signal source, the arriving signal will strike any given identical points on the two antennas simultaneously. However, if the signal is arriving from a source above or below the horizontal plane of the antenna, the previous statement is no longer true. For example, if the wavefront is from a source below the plane of the antenna, the signal will arrive first at the lower antenna and the signal voltage from the top antenna will lag the signal from the lower antenna. The signal voltages at the antenna output terminals will no longer be in phase, and partial cancellation will take place. The opposite is true if the signal arrives.

The angle of arrival and the resultant difference in arrival time causes a phase difference which reduces the magnitude of the combined voltages. You should begin to see now why two vertically stacked, identical antennas have a more restricted "vision" to signals arriving from a point above or below the horizontal plane than does a single antenna.

HORIZONTAL STACKING

Stacking two identical antennas side by side in a horizontal plane significantly narrows the horizontal beam-width angle. That is, the antenna combination, like a horse wearing blinders, "sees" fewer interfering signals arriving from the sides while its vision up and down (in a vertical plane) is virtually unaffected. In the process, gain increases approximately 1.2 dB over that of a single antenna.

If two identical antennas are arranged side by side in a horizontal plane and the signal wavefront arrives directly from the front, each antenna "sees" the same wave or field at the same time. If the wavefront arrives from a source above or below, the same is still true, except that the individual antennas are not operating as efficiently. However, if the wavefront arrives from one side or the other (Fig. 5A and C), the antenna on the side from which the signal is arriving will "feel" the signal first, causing the voltages induced in each antenna to be out of phase. This, in turn, causes partial cancellation of the antenna voltages when they are combined.

The up and down (vertical) "vision" of a horizontal stack is comparable to that of a single antenna, but its side-to-side "vision" is more restricted.

QUAD_STACKS

Stacking four identical antennas, two vertically and two horizontally in a rectangular or diamond pattern, restricts the vision of this combination in all directions off the axis. Called a quad stack, it "sees" as though it were looking through a tube pointed in the direction of the transmitting antenna.
Gain is increased approximately 4 to 5 dB over that of a single antenna.

GENERAL TECHNIQUES

Before you start putting up an array, you should be aware of the following basic considerations which apply to dual and quad stacking of antennas:

1) Stack only identical antennas
2) Maintain approximately one wavelength spacing (at lowest channel frequency) between antennas
3) Cut phasing lines or connecting cables to equal lengths
4) Length and phase oftwinlead interconnecting harnesses is critical
5) Horizontal supports should be nonmetallic
6) Avoid running interconnecting cables horizontally.

Vertical stacking is easier than horizontal stacking simply because in vertical stacks theantennas mount on a common vertical mast and spacing is easily adjusted.

However, with the excellent gain and high directivity of most Yagis today, vertical stacking is seldom necessary. If additional gain is needed, two vertically stacked identical antennas spaced more than ‘/2 wavelength apart will increase signal power by 3dB compared to that of one antenna. However, part of the increased gain will be lost in the connecting cables and the coupler.

Horizontally stacked antennas also must be spaced so that their booms are separated by a distance equal to more than ‘/2 wavelength of the lowest channel frequency. This spacing is needed to prevent the tips of the longest reflector elements from touching. Also, the horizontal supports must be nonmetallic; redwood or cedar 2’ x 4’ s are commonly used.

The severe ghosts caused by high-rise buildings, water towers and mountains can be reduced or eliminated by horizontallystacking two Yagis. However, the wavelength of a channel 2 signal exceeds 17 feet, making such an array for channel 2 unwieldly, heavy and subject to damage from ice and/or high wind. Fortunately, ghosting is more of a problem at high-band channels, and highband antenna dimensions are significantly smaller. For these reasons, usually only high-band Yagis are stacked horizontally.

Thanks for the info on stacking antennas. Airplane flutter could be a problem for us, so I think I'll go with a vertical.

I was thinking about increasing the F/B ratio. This sounds pretty stupid, but what would happen if you used an active element on the rear (combined out of phase) to increase the F/B Ratio. Say you put two SGBH antennas back to back, and combined them out of phase. What would the polar pattern look like?

Say you put two SGBH antennas back to back, and combined them out of phase. What would the polar pattern look like?

Yeah, I thought about that too, except with even more elements. Kind of like a yagi or log periodic type antenna, increasing and decreasing in size.

Its going to take more modeling to know, and when getting up into the high db gain range, the law of marginal utility starts to apply.

I have violated that law many times, and have paid the penalty. :p:D

oh... that's another idea. What if you had two diamond structures, one bigger and one smaller.

You mean a larger one for the top of a DBGH and a smaller one for the bottom section ?

If you look a couple of pages back, thats what the commercial SuperG antenna picture looks like. (Hard to tell for sure without the exact dimensions). If thats the case, I think they are trading increased gain for increased bandwidth in the channels above 51, which no longer exist after next February.

No.... I meant more of a structure within a structure. One tuned to lower channels, and the other to higher channels.

Sorry if my madd Paint skills blow you all away, but here's the concept drawing of my idea to create multiple diamond structures. The black stuff would be the original elements, and the red would be the added stuff:

http://radioguy.googlepages.com/SBGHIdea.png

Hmmm, it looks like your idea is another antenna inside of the shape of the first antenna, and the two are connected. (might as well include the second stubs too, as they play an important role in the gain of the SBGH) My guess is it would act to increase the bandwidth just like using a much thicker element. (like a bowtie increases the bandwidth of a simple dipole) But from what I understand, the thickness of the element can only go up so far in uhf frequencies.

Exactly. The whole idea is to increase bandwidth to get just that much more performance out of it. Don't know if it would help, but I thought it's worth a shot to model. Ideas are free.

Increasing bandwidth lets you get a bigger range of frequencies, but gives less gain. For example a yagi, adding more directors narrows the bandwidth and increases the gain. For the SBGH, the range of frequencies for the uhf band is great for after next February, it just needs to be downshifted a hair more for channel 14. A DBGH does downshift the freq somewhat.

After next February, some commercial antenna designs may decrease their bandwidth to increase gain. And more importantly in the vhf range, to decrease the size of those monsters.

Just a quick question: I've got a bunch of small sections of normal sized antenna tubing (from some junk antennas) which I'd like use as reflectors.

Is this optimal, or should I ask, will it lower my gain much??

You could have used DogT's trick for straightening wire. Cut longer than needed. Put one end in vice and clamp other end with vice grips sideways. Tap vice grips hard a few times with a hammer. It does a very nice job.

Is this optimal, or should I ask, will it lower my gain much??
You mean build the colinear rod reflector model like I did ? (look a few pages back in the thread for pics) You only lose .5 to 1 db max, but it has other advantages, like less wind loading and weight.

Oh ...no. That's not what I meant. I'm planning on building a reflector out of chicken wire.

I'm talking about the active element section. I'd like to use my pile of small antenna elements rather than #8 wire. How is this going to affect performance?

I'm talking about the active element section. I'd like to use my pile of small antenna elements rather than #8 wire. How is this going to affect performance?

Basically, using wider wire/tubing will give you greater bandwidth up to a point. Just quickly looking at the yagi antenna designer, Link : http://www.k7mem.150m.com/Electronic_Notebook/antennas/yagi_vhf_quick.html
For channel 52, 700 mhz : It is recommended that the element diameters be limited to between 0.001 and 0.02 wavelengths. At 700.000 MHz, this is 0.017" (0-1/64") to 00.337" (0-11/32"), or 00.428 mm to 8.566 mm. The idea here is to keep the diameter small in relation to the element length. Thus, as frequency increases, the useful element diameter decreases.

And at 470mhz, channel 14, : It is recommended that the element diameters be limited to between 0.001 and 0.02 wavelengths. At 470.000 MHz, this is 0.025" (0-1/32") to 00.502" (0-1/2"), or 00.638 mm to 12.757 mm. The idea here is to keep the diameter small in relation to the element length. Thus, as frequency increases, the useful element diameter decreases.

So, bottom line, 3/8 (10mm) is too big for channel 52 but fine for channel 14. It really depends on how your stations are spread.

Sorry for the double post....

I'm ready to build my monster 30" X 75" DBGH. I'm just gonna double check all the fine details first. After this, I'm gonna take the plunge!!!

- So, the screen will be 30 x 75 chicken wire. Where to I "split" it, how wide should the gap be, etc....?

-I'm gonna go with a 95MM feed gap. That's 3.7," right?

-I'll be using #10 insulated wire. If my calculations are correct, I'll need 18 ft of it.

-Top and bottom bays are 5" apart. Has anyone optimized this?

-Depth from screen to element is 3.9," or 100mm. Has anyone played around with this?

-Feed line between bays: how exactly do I install it?

I was seriously expecting to find that I had make some little quirk in my construction that somehow canceled out all signal or something bad like that. So glad to see it actually worked ...and it works so well, especially considering that it was sitting right on the ground. I can't wait to see what happens when it's 35ft up in the air!!!! Hello, Chicago DTV ;););) (maybe not).

Oh... I forgot to mention that channel 18 is also used by a very strong DT station in about the opposite direction. I don't know what that would do to WQOW's picture. KPXM 41 (ION) is a pretty long shot at 110 miles. They do have a pretty high tower, though. WKBT 8's DT is on 41, and is fairly strong. I think getting a color picture on 41's not quite out of the question, but don't quote me on that. Fortunately, their moving to the TC towers (where 17, 23, 29 and 45 are) come 2009, so reception will be a breeze.

Again, thanks for all the work that got put into the design.

I was seriously expecting to find that I had make some little quirk in my construction that somehow canceled out all signal or something bad like that.
Its a fairly simple design and as long as the dimensions are followed and everything is straight and flat, success is pretty well assured. (sometimes, even when its not straight and flat, results are amazing, heh)

Of course, a bad balun, which happens fairly often, could make someone think its bad. Overtightening a balun can destroy it.

I built my 30" x 75" screened DBGH a few weeks ago
I can't wait to see what happens when it's 35ft up in the air!!!!

I just caught that, heh. Whats going to happen is, its liable to fall over and break in a wind greater than 40mph. While screening is an excellant and economical material (especially if youre already replacing screen on a large door) to use for the DBGH reflector indoors, outdoors its going to catch a heck of a lot of air. Youre really going to need a serious guy wiring setup to hold it.

Oh.... no. I didn't use window screen or something. It's good ol' chicken wire. I'll post pics of it soon. I think I'm gonna replace the hacked together scrap aluminum antenna tubing frame with some PVC pipe, though.