Rookie Builder SBGH Element Questions - Canadian TV, Computing and Home Theatre Forums

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post #1 of 8 (permalink) Old 2018-08-01, 10:43 AM Thread Starter
Join Date: Aug 2018
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Rookie Builder SBGH Element Questions

Gents, just registered and have to say, this is one impressive web site. The scope of the forums and subjects is enough to keep a guy busy for a good while!

Okay, to hand. I have built one antenna before. A bow tie model using copper wire straightened out for the elements and phase wires. Mounted to a 1" square tube on plastic insulators. Set in my mum's living room and it works pretty well. I have also wanted to try the GH model since it looks to be a bit less tedious to build. I am an electrician by trade so bending things to precise angles and measurements comes easy to me. The GH looks to be a good design for my area. About 35-40 miles from towers to my direct east and west. Mostly a straight LOS to each city. Strong broadcast towers. All channels run mid to upper range UHF save for one PBS at channel 18, and two VHF hi stations at 11 and 13.

Okay, the question(s). I have looked at this design for awhile and understand it was originally for the larger spectrum of 14-83. I also understand the FCC reduced the spectrum to channels 14-51 starting in 2009 which would necessitate a bit of a change in design. I have looked at the links to designs like GH0, GH6, GH10, etc. One thing I am not completely sure of is the element sizing. The original had I believe 8 equal length bends of about 7"/180mm. I have also seen some that keep the 7" bends but shortened the top and bottom horizontal elements to around 5"/127mm in an effort get the antenna more in line with the new frequency range.

Now about those GHxx models. I noticed most have unequal length bends in each element. This is not a hard thing to sort for length since distances between bends is listed. But are they all bent 90 degrees like the original or are the angles adjusted to keep a consistent vertical distance between the two elements themselves? Bending each to 90 degrees would be easier though I realise that would mean differing distances between each 'point' of the elements where they meet at the mast.

I really don't want to use a reflector since our signals are good and it will let me keep the antenna pointed one way and allow reception East to West with no rotator. For the designs with unequal length element bends, are they designed to work with reflectors? I guess the shorter way of asking things is what design should I be looking at for NO reflector? Also, will likely add NARODs for VHF but it is not really necessary. I just thought it would be neat to try it.

Thanks for reading this and sorry to be long winded. I can also tell you I need to get this sorted because my family and friends will want a few for themselves and you know who is going to get volun-told to do it.
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post #2 of 8 (permalink) Old 2018-08-01, 12:07 PM
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Location: Rockwood, ON
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nikiml has a bunch of optimized GH designs at his website: nikiml's Antenna pages

For the ones with no reflector, you can look for GH0. I can't speak about the angles of the bends, but just eyeballing it looks like they're not quite 90°.

The optimized GH0 for UHF is here: nikiml's Antenna pages - GH0 UHF antenna

But if you wanted to add the narod elements for VHF-HI, it would also improve UHF gain. The gain pattern for VHF-HI is just out of the front, but UHF gain would still be front and back (a bit more in the front). That one's called the GH0n3: nikiml's Antenna pages - GH0n3 UHF/VHF-hi combo antenna

36' 8200U-KT200-HDHR#1067A7DF / 33' DB8e-CM7777-HDHR#1067A183
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post #3 of 8 (permalink) Old 2018-08-01, 05:11 PM
Join Date: Nov 2008
Location: San Diego, CA
Posts: 3,393
The "Original" SBGH was an evolution of the HOVERMAN and earlier CHIREIX Antenna, wherein all Diagonal Elements were the SAME Length at SAME 45-deg Angle. Unfortunately, since they were "Single Frequency" Resonant designs, none of them had enough Bandwidth to cover the "original" UHF Band from 470-806 MHz, although the HOVERMAN had almost enough Bandwidth for the "new" UHF Band (470-698 MHz). When the Hoverman's Outer Elements were shortened nearly 2-inches and moved to the Horizontal, it became the "Original" SBGH: [Chireix] [Hoverman] ["Original" SBGH]

The Optimized G-H Antennas found on nikiml's website eliminated the CONSTRAINTS of Equal Lengths at 45-deg Angle, allowing different Lengths at arbitrary Angles. This allowed "Stagger Tuning" to widen the Bandwidth [resonating at different frequencies], with additional "Degrees of Freedom" to facilitate Optimizing the Gain and SWR Performance.

In nikiml's nomenclature, "0" after the name (e.g. GH0) indicates NO Reflector, GH2 means 2 co-linear Reflector Pairs, GH4 means 4 co-linear Reflector Pairs, etc., as shown in each "MODEL". An "n" after the name indicates that it includes additional Elements (e.g. Top Hats that are passively "coupled" to the GH) to improve Hi-VHF Performance.

If you download each 4nec2 file, you can see the X,Y,Z Coordinates, although it is difficult to "decode" what is going on. It would help to correlate SYmbol X,Y,Z Coordinates and Element Lengths in the 4nec2 file to the various wires in the MODEL on nikiml's website, by selecting a particular G-H Design Number and then Select "MODEL". You can select (default) mm or inches in bottom-left and view in bottom-right. Roll over Element Ends and Middles to see X,Y,Z and Lengths respectively. Angles are NOT provided...nor should you "need" them, relying on X,Y,Z Coordinates.

You might want to compare to the fol. "Free-Form" [i.e. "Stagger-Tuned"] FF4 4-Bay Bowtie and FF6 6-Bay Bowtie Designs, with NO Reflectors:

Note that both of these improved Bowtie Designs is a significant improvement on the GH0 (which provides 7.8 to 11.9 dBi Gain), which is not included in below [NO Reflector] UHF Comparison Chart:

Antenna Simulations, Overload Calculations, etc:

Last edited by holl_ands; 2018-08-01 at 06:12 PM.
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post #4 of 8 (permalink) Old 2018-08-01, 09:44 PM Thread Starter
Join Date: Aug 2018
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Orbot, holl and, thank you for the great replies. And particularly sorting out some of the GH nomenclature. Indeed I have actually been to nikiml's site. I manage to find the menu buttons that allowed me to roll over the elment images and jot down some measurements. That is why I asked about bend angles. I could tell immediately there was no way to align the two elements along a common veftical line if they were all bent to comkon angle. Too many years of bending conduit put the image in my head straight away.

So I am assuming(you know what that gets you)that his 'coordinates' correlate to some bending angle. Sorry to sound ignorant but when you say I shouldn't need the bend angles, is there something in those files that tells you how/where to make the bends? This ismpretty new to me and I am not even sure what I am looking at when I view them.

And I will check into those bowtie antennas as well. BTW, I know adding NARODs to a GH(non-conductively)makes the difference. For the bows, do they need additional elements as well? It seems I once saw an image of one with straight elements projecting from the sides and connected directly at the same junction the phase wires are tapped for the balun. Yes/no? Agsin, thank you for the prompyt replies. It really helped.
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post #5 of 8 (permalink) Old 2018-08-03, 07:54 PM
Join Date: Jul 2017
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Satch, message me , I have a video which explains how to create the GH element with exact 7in bends.

Last edited by Groundedforlife; 2018-08-03 at 08:12 PM. Reason: Add photo
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post #6 of 8 (permalink) Old 2018-08-05, 06:53 PM
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nikiml provides X,Y,Z Coordinates for where the Apexs should be, where X is in direction of Tower, Y is Sideways and Z is Up.
Probably easiest is to lay it out on a piece (or two) of Scrap Cardboard and then bend metal to fit the need to use trigonometric formulas to calculate angles.

NAROD improved G-H Performance in Hi-VHF Band (esp. SWR).

I have NOT pursued NAROD type approach with Bowties, but I HAVE Analyzed adding a [Passive] LOOP (or two) to Bi-Directional Bowtie Antennas....with NO Interconnection to Bowties. If you open the last FOLDER at bottom of this page, you will see all of things I and others tried to design a Hi-VHF/UHF Antenna that FIT within a 3-ft H x 2-ft W METAL PICTURE FRAME that someone wanted to remain out-of-sight in their Apartment:

The BEST of these CONSTRAINED 3'x2' designs [by MagiMaster] was the fol. 2-SQUARE CENTIPEDE that is CLOSELY COUPLED to the surrounding LOOP [which was TOO LARGE to resonate in Hi-VHF Band]. The close coupling to the Loop (NOT interconnected) is "similar" to the NAROD close coupling approach:

The several ALBUMS just above that FOLDER analyzed 2-Bay and 4-Bay Bowtie Antennas with Optimized RESONANT LOOP(s) which very successfully improved Hi-VHF Gain and SWR. Here's the RLH4 Optimized 4-Bay with two Hi-VHF Resonant Loops. Note that close coupling was NOT required to get this approach to work:

For a high gain, directional antenna the usual Screen Grid or Reflector Rod Reflector System could be added....

Antenna Simulations, Overload Calculations, etc:

Last edited by holl_ands; 2018-08-05 at 07:20 PM.
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post #7 of 8 (permalink) Old 2018-08-09, 06:35 AM
Join Date: Jan 2009
Posts: 4,597
Of course Nikiml provides the angles needed to bend..
It is easy to get the angles for bends from nikiml's necviewer..

1.) In Nikiml's Necviewer, CLICK on a wire until it shows the Length, x,y,z coordinates, etc. The wire will turn to Pink.
2.) then CTRL-Click on the wire next to it for which you would like the angle between wires. The two wires will
turn to Pink and It will now display the angle between the two wires that were Clicked, Ctrl-Clicked (selected).

3.) to clear that selection to grab the next angle, double click anywhere in the white space (wires will no longer be Pink)
and repeat 1 and 2 until your are done.

so in a nutshell
After some Click, Ctrl-Click, Clear - Click, Ctrl-Click, Clear - Click, Ctrl-Click, Clear ....
You will have all the angles you need.
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post #8 of 8 (permalink) Old 2019-08-13, 04:48 PM
Join Date: May 2009
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Oh, that is amazeballs in awesomesauce!

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