GH "Gold Standard" for UHF (Plans, Notes by j3d)

[Autofils]

It's been a while since I have checked in on the forum, and I see a lot of changes have been made.
So my congrats to Stampeder for those changes.

This posting provides important update information for the GH collinear rod reflector design, that will likely be of interest to all forum members.

I just recently received an email from Old Sparks that provided a link to some further optimizations of the GH collinear rod reflector design made by John E. Davis. I contacted John, and he granted permission to post a link to his web page.


Updated GH Collinear Rod Reflector Design by John E. Davis

John's work has progressed the GH antenna design in two important areas:

1. John's optimizations provide a better GH design over the entire new UHF band of 470-700Mhz. The gain is amazingly flat over the UHF band-width !!
2. His narrow-band design shows the max GH gain at reduced bandwidth, which is applicable to those seeking reception of specific distant channels. I'm sure this will perk interest in double bay Narrow-band designs for those "hard-to-receive" channels. It has certainly revived my quest for wnpi on Ch 23, and I'll be looking into a double-bay narrow band design....mlord...perhaps there is still hope...

His web page provides Netgain, SWR and F/B results for four collinear rod reflector designs, as well as the design parameters and dwgs, that contain all the info needed to build any of these designs.

For those that want a GH design that covers the entire post 09 UHF band (470 to 700Mhz), these designs are the best, and John has provided four options, from the simplest GH4 to the higher gain GH10 collinear design.


To have a detailed look, here is John's Web Site..
http://www.jedsoft.org/fun/antennas/dtv/gh.html

[stampeder]

Wow, John's done some terrific work optimizing them - will he be signing up here so we can discuss his improvements with him?

[Autofils]

Originally Posted by stampeder

Wow, John's done some terrific work optimizing them - will he be signing up here so we can discuss his improvements with him?

Stampeder,

In my email exchanges with John, I suggested that he join, but has currently declined the invitation. Perhaps once he sees the response in this thread to his work, and the high traffic on his web page, he will change his mind.
Maybe I can get him to start a new thread on MURS band antenna design, that he is currently working on.
[ What is the MURS band? ... look here ....http://www.provide.net/~prsg/murs_faq.htm#Q5. ]


The Hoverman array is a very interesting design, that can be "excited" in quite different ways, simply by adjusting the collinear reflectors, and John's work clearly shows this effect.

I've found another interesting effect of this in my quest for a good FM antenna and I will be using some of John's optimization methods in this combo GH design (VHF-Hi and FM). I'm shooting for VHF-Hi 11-12 dbi with swr <2.5; and FM 6-9dBi with swr <4 with a max height of about 50-55 inches. Hey, if this pans out, it can easily be scaled for MURS !!

[300ohm]

Interesting, he's varying the reflector gap, increasing it from middle to top/bottom. Makes sense. I also found that decreasing the gap on my SBGHgen2_2X4CurvedMesh reflector from 1 inch to .2 inch decreased the small dip in the middle of the gain curve I had. Ill have to model a similiar middle to top/bottom change to my Curved Mesh reflector.

As the plots show, the antenna appears to be quite tolerant of construction errors on the order of plus or minus 1/8 of an inch (3 mm).

Definately. Out of the types of antennas Ive modeled so far, the GH is far and away the most forgiving. Make a tiny change in a corner reflector yagi model and the gain curve goes wacky, heh.

[mlord]

Originally Posted by Autofils

It has certainly revived my quest for wnpi on Ch 23, and I'll be looking into a double-bay narrow band design...
mlord... perhaps there is still hope...

If you can design it, I can build a couple for us to play with!

Cheers

[ctgottapee]

one thing that isn't made quite clear in his diagrams is that it appears the reflector elements are offset from the antenna differently. the reflectors nearest the top or bottom of the antenna don't line up parallel with the stubs

i also see he is going with an element/reflector diamerter of 1/8 inch which is almost 1/4 the size of the 3/8 inch suggestion in some of the GH build plans

and a double bay design sounds great, but nobody has yet really fully modeled the interconnection between the two bays. that and the issue that it becomes a 10 foot tall antenna - or giant spear of the gods in case of tornado

personally, while i don't want to discourage you guys as i could use your experience, i don't believe a db or so extra is going to help pull in ch23.

i can't express enough though how a new tuner would be your best shot, the new Fusion7 is just amazing. i know most the new SD DTV STBs generally have the newer chipsets and silicon tuners which should also give you an idea if you can get one of them.

i'm getting a ch18 and ch22 at 57miles -110dbm tvfool with an 8800 and CM7777 mounted at 27feet, both at 100% and 27-30db

[Autofils]

Originally Posted by ctgottapee

one thing that isn't made quite clear in his diagrams is that it appears the reflector elements are offset from the antenna differently. the reflectors nearest the top or bottom of the antenna don't line up parallel with the stubs

ctgottapee,

Indeed the collinear reflectors have a different offset.
This is the main reason why the bandwidth is wider and now covers the entire post 09 UHF band.
Also you'll note that the reflector gaps vary per reflector pair, the array length is a bit smaller compared with the earlier GH designs and the feed-point gap is larger.

This design covers the entire UHF band and provides a relatively flat gain pattern across the entire band. This gain flatness is a characteristic that has not been achieved by other antenna designs such as the wide-band lpda yagi, or the 4Bay Bowtie, and thus makes this design unique !!

For that reason, I would recommend that this design should become the SingleBay "GH Gold Standard" design. There are currently four versions to choose, depending on what gain you desire.

Perhaps we will soon see a DoubleBay version ??
...any takers ... after all this is an R&D thread, is it not !!...



John's dwgs provide the complete detailed geometric information for the antenna on the dwgs on his web site.

The reflector dwg:
The vertical reflector offset distances are stated with respect to the array feed-point (variables z1, z2, z3 ...etc.) and the distance between adjacent reflector pairs are the "delta z" parameters.
The lengths of each reflector pair element are the L parameters (L1, L2, L3 ..etc) and the gap between reflector pairs is stated by the g1, g2, g3...etc parameters.

The array dwg:
For the array element, the diagonal length is stated by "a", and the length of the horizontal stub is stated by "b". The vertical height for the all the bends with respect to the feed-point is stated by "z1, z2, and z3" ( In the orig design, this was the "h" parameter). The feed-point gap is stated by the "g" parameter.

The reflector spacing (center-to-center) between the reflector-pairs and the array elements is stated by "delta X".


The wire diameter for the array and reflectors is 1/8".
( I have a feeling that a wire diam of 7mm, used in the orig GH designs, would improve the swr, but I have not yet modeled it....it's on my to-do list)

[stampeder]

Originally Posted by Autofils

I would recommend that this design should become the SingleBay "GH Gold Standard" design

Indeed, the king is dead, long live the king!

I'm assuming that this means that the mesh reflector GH versions are not going to be able to match the performance of the collinear rod versions even with tweaking - is that a correct assumption?

[Autofils]

Originally Posted by stampeder

I'm assuming that this means that the mesh reflector GH versions are not going to be able to match the performance of the collinear rod versions even with tweaking - is that a correct assumption?

Stampeder,

300ohm has done much more modeling for mesh screens, than I, and he can perhaps provide more insight.

From the small amount of mesh screen models that I have done compared with collinear rods, I found that the "tuning-effect" with the collinear rods, having different lengths and vertical positioning, is able to provide a gain-boost at the lower-end of the UHF band that a full mesh-screen(split or unsplit) may not be able to achieve to the same degree of flatness of the overall gain response.

Normally for full screens ( split or unsplit) the lower freq response is mainly determined by the width of the screen and the gain has a rising characteristic as the frequency increases. Normally the peak gain will be higher by 1-1.5db than obtained by collinear rods.

However, I suspect that if you used mesh screen to, in essence, make "fatter" collinear elements, a similar or improved response might be possible.

[stampeder]

Okay thanks for that - It'll be interesting to see what 300ohm has to say too.

One of the factors for choosing a mesh version over a rod version is its ease of use for builders, but I'll bet most will be interested in any mesh tweaks that make use of the new design's features.

[astupidoldman]

The numbers are great. I say that with a smile cuz I am just now getting to a point where I can get the nec software to put out the numbers you guys have for the same models. There is so much tweaking I have to learn, plus the cards and so on, but I'm getting there. I will be elaborating in my contraption thread soon if I can stop playing with the models. I have many questions. I've been working really hard on the phase line thing. My idea for a single mast quad is baked, but I have several models with double and triple bays and some look really promising. I hit over 18 dB raw, with one and AGT's are better, but I am really coming up with off the wall phasing lines.

Once I get the right phase line design, I want to replace the SBGH's with the new GH Gold Standard. Currently working on 444 to 512 mm as the half length of the phase line. The trick is not to lose the gains that he produced. At best, I can up his gains(total, if I've done the right formula on the spreadsheets) by only 0.5-1dB, but lose it on the other freq's. I am not quite understanding yet that if you lengthen a, it improves b but drops the other thingy ma jig which makes the dohicky go all over the place, but not where I want it.
Anyway, gotta bail for work so I don't have much time. I'm printing up some of the help files(rtf) in the exe folder and others to read at work. I have to learn how to ask the right questions to get the answers. I am so addicted to this now, I may need an intervention.

[Autofils]

In an earlier post, I mentioned that the mid-hump in the SWR of the GH-(jed) designs might be affected by the choice of wire diameter.
I ran 4nec2 on the GH4 (jed) design for wire diameter of 3 and 7 mm and here are the results.
The SWR plots clearly show the improvement in SWR for 7mm diameter. I didn't calculate the Net gain, but this SWR improvement will increase the net gain somewhat and will make the gain characteristic smoother.

SWR Compare

Wire Diam= 3 mm


Wire Diam = 7mm


Rawgain Compare

Wire Diam = 3mm


Wire Diam = 7 mm



Here is my nec file for wire diam =7

===========================================
CM SBGH GH4 Collinear Rods design by John E. Davis
CM (wire Diam =7mm for array and reflectors)
CE
SY y=0.112 'FeedGap spacing
SY x=0.107 'Length of Array Horizontal Stub
SY h=0.14 'Array Diagonal length = [Sqrt(2) xh]
SY s=0.096 'Reflector Spacing
SY g1=0.032 'Reflector pair R1 gap
SY g2=.026 'Reflector pair R2 Gap
SY R1=0.319 'Collinear reflector R1 length
SY R2=0.303 'Collinear reflector R2 length
GW 1 7 0 -y/2 0 0 y/2 0 0.00302
GW 2 10 0 y/2 0 0 y/2+h h 0.0035
GW 3 10 0 y/2+h h 0 y/2 2h 0.0035
GW 4 10 0 y/2 2h 0 y/2+h 3h 0.0035
GW 5 10 0 y/2+h 3h 0 y/2+h+x 3h 0.0035
GW 6 10 0 y/2 0 0 y/2+h -h 0.0035
GW 7 10 0 y/2+h -h 0 y/2 -2h 0.0035
GW 8 10 0 y/2 -2h 0 y/2+h -3h 0.0035
GW 9 10 0 y/2+h -3h 0 y/2+h+x -3h 0.0035
GW 10 10 0 -y/2 0 0 -(h+y/2) h 0.0035
GW 11 10 0 -(h+y/2) h 0 -y/2 2h 0.0035
GW 12 10 0 -y/2 2h 0 -(h+y/2) 3h 0.0035
GW 13 10 0 -(h+y/2) 3h 0 -(h+x+y/2) 3h 0.0035
GW 14 10 0 -y/2 0 0 -(h+y/2) -h 0.0035
GW 15 10 0 -(h+y/2) -h 0 -y/2 -2h 0.0035
GW 16 10 0 -y/2 -2h 0 -(h+y/2) -3h 0.0035
GW 17 10 0 -(h+y/2) -3h 0 -(h+x+y/2) -3h 0.0035
GW 20 18 -s (R1+g1/2) -2.893h -s g1/2 -2.893h 0.0035
GW 21 18 -s -(R1+g1/2) -2.893h -s -g1/2 -2.893h 0.0035
GW 24 18 -s (R2+g2/2) -0.879h -s g2/2 -0.879h 0.0035
GW 25 18 -s -(R2+g2/2) -0.879h -s -g2/2 -0.879h 0.0035
GW 26 18 -s (R2+g2/2) 0.879h -s g2/2 0.879h 0.0035
GW 27 18 -s -(R2+g2/2) 0.879h -s -g2/2 0.879h 0.0035
GW 30 18 -s (R1+g1/2) 2.893h -s g1/2 2.893h 0.0035
GW 31 18 -s -(R1+g1/2) 2.893h -s -g1/2 2.893h 0.0035
GE 0
LD 5 0 0 0 24900000
GN -1
EK
EX 0 1 4 00 1 0
FR 0 0 0 0 700 0
EN

========================================================

[mlord]

Sweet !

[300ohm]

300ohm has done much more modeling for mesh screens, than I, and he can perhaps provide more insight.

From the small amount of mesh screen models that I have done compared with collinear rods, I found that the "tuning-effect" with the collinear rods, having different lengths and vertical positioning, is able to provide a gain-boost at the lower-end of the UHF band that a full mesh-screen(split or unsplit) may not be able to achieve to the same degree of flatness of the overall gain response.

I found that to be true too, but the trade off looks to be gain on the middle channels. But keep in mind, I really havent tried to peak for channel 14. My channel 14, a low power station 2 miles away, is one I prefer to tune out completely, heh. The gen1 curve is really fine for me.

Normally for full screens ( split or unsplit) the lower freq response is mainly determined by the width of the screen and the gain has a rising characteristic as the frequency increases. Normally the peak gain will be higher by 1-1.5db than obtained by collinear rods.

Thats true for the gen1. But remember, I had a hard time matching the gen2 GH10 without resorting to the curved mesh - swept elements. The DBGH gen2 curved mesh/swept elements will do about 16dbi from about channel 23 to 18.2 dbi or so up to channel around channel 42 IIRC. Then the rapid fall off. Still havent tried curving the colinear pair reflector elements, but that needs to be tried. Mclapp does it on his rod reflectors on with his winegard style flat element bowtie with good results.

However, I suspect that if you used mesh screen to, in essence, make "fatter" collinear elements, a similar or improved response might be possible.

Yeah, Ill eventually play around with changing the mesh reflector gap spacing in a variable way, that looks like it has some interesting potential. The trouble with the mesh designs with 6 to 9 thousand segments is that they take many hours to compute per run. Doing Stampeders CM1111 takes seconds per run. Its actually a refreshing change, heh.

I am so addicted to this now, I may need an intervention.

Only one cure, build another antenna, heh.

[astupidoldman]

Speaking of which, ideally the next build will have a lot of copper, footprint has to be small as I want to be four feet higher. That’s twenty feet off my deck and the mast will stay exactly vertical a lot longer with less weight. The fiber glassed lumber I have up now is so yesterday. I’m runnin’ this Intel Pentium D 2.66 with nearly 2 gigs of ram and there must be away of not getting 4.e0 for a calculating time on a run. Realized several hours later after a nap, it wasn’t going to spit anything out. I remember something about changing out files in the exe folder to a 10k thingy. Is that how you’re able to run with your screen models and more segments for forward sweeps. And as far as memory goes, I could over clock these two hour runs, but I wouldn’t be utilizing most of the bus to the processor anyway, as I understand it.

So back to the build of the Golden Standard footprint I have to erect off my deck that also must remain mobile for runs in the Jeep. And of course, if anyone complains about it. Mine comes down. Not like the 300 sat dishes in this complex. It would be cool to run in nec, those steel reflectors I used on my model that is working right now…the beast. I’ve collected lots of pvc pipe, but too much of that and I might as well fly a fat kite off my deck. Plus mesh. BTW, mesh would grab air too. I have to find a welders supply or something for aluminum as reflectors. Less pvc, more floating of precious metals in free space. Just a single mast with the latest DB enhancements…or whatever. An ultra light. So instead of mesh, just run rods in nec, instead? Just in the shape of a parabola with it edges extending way past the edge the GH. Another two feet out beyond the edge, deflecting it back to the GH element.

Is there a way to calculate the angle of deflection? Thought I saw something in the build or plans, model. A multi bayed rig would come pretty close to 10000 segments, wouldn’t it? I’m beginning to understand using cards. It would be nice to model the pvc or plastic pipe too. Say 3 and half inch max, the single mast or whatever and the then the metal free floating in space. So many variables to mess with. Anyway, I’m tired. And I just looked at the Nec-2 manual, part III: User’s guide for the fifth time and suddenly realized I was beginning to understand what I was looking at. Must…sleep.

Thank you very much for any help, gentlemen. I wish I could learn faster. I’d rather be building the darn thing. An excuse to buy some more 18.5 volt batteries for my tools!