Autofils,

Thanks for your time and effort! I am going to wait until this project is further along before attempting a GH. So far, my bowtie is doing enough for me in my situation, but I am looking forward to building a DBGH that can cover all of the range I may need post 2009.

I wish I could do more to help, but from the discussion here and the original thread, I am way over my head with the modeling and details. I will simply have to wait until you and others work out the kinks. Until then I am looking for materials at bargain basement prices.

Thanks again!

Holy crap!!! 16dbd for a dual bay. That's pretty darn good. Looking at the HDTV Primer's results, no antenna they've modeled even hits the 16dbd mark.

Looks like youre following the pattern of the SuperG 1483 that we discussed before, that is if in fact it uses 2 different sized Hovermans and its not an optical illlusion in that picture. :p

:o Wow, I must say that I'm very happy to have waited before building my weaterproof DBGH v3 to put on the roof. I'll wait for the plans to give it a try. It's such a drag that I don't have enough spare time to continue to help you out guys ! Great work !

The NetGain plot shows the preliminary data for v3.1x SBGH with 8 collinear rod reflectors for UHF-Lo and UHF-Hi versions.

Hmm, just from a practical building point of view thought, maybe you shouldnt be spending time on 8 or more colinear rods reflector modeling and model a screen/fencing reflector version instead, if you know what I mean. Making a durable colinear rod reflector with the 20mm spacing really consumed most of my time on my building project. Cutting the rods and then inserting them precisely into a piece of plastic tubing and then attaching them. Making 8 or more pairs of them per SBGH makes the job even harder. Using ready made, widely available, fencing material would make production easier and with more horizontal rods, has to have more gain and directivity IMO. I think Mlord would agree. Of course, the term widely available is a tricky one and 1 X 2 inch stuff that Channel Master uses may be ideal. But 2 X 4 inch galvanized fencing is available pretty much everywhere. That in essence then becomes a 16 or more colinear rod reflector on the SBGH. Also as I figure it, 16 X 3mm reflectors would have about the same practical wind load as 8 X 10mm reflectors, even counting the vertical elements.
And with the zig-zag design of the elements, are we sure that vertical reflector parts are in fact bad for gain ?

I also checked with the manager of my local Radio $hack today if they still had any antenna aluminum ground wire. He promptly directed me to antenna guy-wire. After describing what I was after, he checked in the back and said no.
At least their motto still holds: "Radio $hack, you have questions, we have dumb looks".

This is just my two cents.

Autofils,

Since my original DBGH came down in the storm last week, I am going to wait to see your design details on the DBGH Gen2 before I put it back up. I really only look at channel 26 (digital 27) here, PBS from DC. I should be able to easily modify the original DBGH. Let us know what the design differences are and we will put it to use, I can use all the gain I can get. The DBGH worked wonderfully until it came down and my distribution amp died.

DogT

Well it's been quite a while since my last posting. I had a very serious computer burn-out. A motherboard capacitor shorted and blew the power supply amongst other things and maybe the cpu I'm trying to sort what is left of the box ...bummer :(

So I grabbed my old 400 Mhz Pentium II from the closet and I am limping along with that right now. I had kept some notes on all my previous modeling trials, so I was able to re-construct the v3.2x models.

After all this, I am now at v3.3x, using a total of 10 collinear rod reflectors.
I have found that by "tuning" the reflectors for a higher gain, the bandwidth is reduced. Currently the model results show a fairly flat net gain response of around 15dBi over a 100Mhz bandwidth.
This "flat" gain response is not seen with many mesh screen model variations that I have tried, so I am coming to the conclusion that my initial assumption of "finding" a contoured mesh screen is not valid. I would certainly welcome any discussion on this.

Because of this trade-off of higher gain and reduced bandwidth, the entire post 09 UHF band cannot be covered by a single SBGH antenna.

Here in the Ottawa area, there are two NY state DTV stations [WNPI Ch23 and WCFE Ch38], that I and others, are trying to receive, hence my initial modeling has been aimed at tailoring the bandwidth for Ch 23 and 38.

Here is the latest result... v3.3x, which is very close to completion. I am still exploring improvements, but it now appears that the "law of diminishing returns" is setting in.

The gain response of the SBGH 6 Pair rod reflector GPLv3 design is shown for comparison.
http://i258.photobucket.com/albums/hh262/autofils/GenerationIIGHv33x.gif

Here is the latest result... v3.3x, which is very close to completion. I am still exploring improvements, but it now appears that the "law of diminishing returns" is setting in.

Yeah, thats a tough law to violate, the penalties are severe.:p It looks very nice. Id like to build it. What are the dimensions ? (I could build from the NEC file if you send it to me. Or I could draw it out on graph paper, scan and post it here to save you some time). Also if this version 3.3 was used as the lower part of a DBGH, and using that other "high" version as the top part, is there a some penalty using 2 slightly different antennas versus 2 that are exactly the same ? (I may make a DBGH like that for now, but Ill make it so that after February I can easily replace the "high" part with another "mid" part. For all practical purposes, channel 42 will be my highest channel that Ill watch then.)

It also will be interesting to test the graph versus real life perfomance. My analog channel 57 should then perform worse than a dipole, according to the chart. It would be hard not to see that kind of a difference, heh.

On another note, I realized after I put my DBGH up, that I didnt measure the feedines to be equal, I had just eyeballed them for equal shape. Sure enough, they were 9mm different in length. I replaced the feedlines with some open wire 300 ohm I had, cut exactly to the nearest half mm. I have noticed a tiny bit more gain, but very little. So that means your design for the feedlines on the DBGH is very very close, using 10 gauge solid copper wire.
When I fix my original feedlines and put them back up, I may try a 10mm spacing to see if I get any more gain. According to this site http://www.qsl.net/co8tw/openline.htm it should put the impedence of the feedline down to about 250 ohms.

Looks like the Gen2 SBGH has about the same gain as the Gen1 DBGH at least at my primary channel, which is virtual 26, real 27 which is about 15.5db. I too would be interested in building this creature since my antenna is down at the moment.

DogT

I've had numerous requests to make available the SBGH Gen2 dimensions.
The optimizations are not complete and I don't have much free time, so, in the spirit that others can take this information and provide detailed drawings, I am posting the results of the GH10 UHF-Mid design, which was aimed for local Ottawa users with peak gains at Ch 23 and Ch38.

The results were obtained using 4nec2 v5.7.3.

Here is the AGT Test Results.

http://i258.photobucket.com/albums/hh262/autofils/GH10AGTTestResults.gif

Here is the SWR PLot

http://i258.photobucket.com/albums/hh262/autofils/GH10Gen2UHF-MidRodReflectors-Swr.gif


Here is the Raw Gain

http://i258.photobucket.com/albums/hh262/autofils/GH10Gen2UHF-MidRodReflectors-RawGai.gif

Here is the nec SY Variable file. ( Just copy and paste and save as GH10.nec)
All dimensional data is stated in the nec file and is in meters.



-----------------------------------------------------------------------
CM SBGH Gen2 GH10 Collinear Rod reflectors
CE
SY y=0.095 'FeedGap
SY x=0.094 'Length of Array Horizontal Stub
SY h=0.163 'Length of Array diagonal = (Sqrt(2) * h) = 0.231
SY s=0.094 'Reflector Spacing
SY g=0.05 'Reflector Gap
SY R1=0.227 'Collinear Rod Reflector Lengths
SY R2=0.370
SY R3=0.495
SY R4=0.268
SY R5=0.392
GW 1 5 0 0 0 0 y 0 0.0029
GW 2 10 0 y 0 0 y+h h 0.0035
GW 3 10 0 y+h h 0 y 2h 0.0035
GW 4 10 0 y 2h 0 y+h 3h 0.0035
GW 5 10 0 y+h 3h 0 y+h+x 3h 0.0035
GW 6 10 0 y 0 0 y+h -h 0.0035
GW 7 10 0 y+h -h 0 y -2h 0.0035
GW 8 10 0 y -2h 0 y+h -3h 0.0035
GW 9 10 0 y+h -3h 0 y+h+x -3h 0.0035
GW 10 10 0 0 0 0 -h h 0.0035
GW 11 10 0 -h h 0 0 2h 0.0035
GW 12 10 0 0 2h 0 -h 3h 0.0035
GW 13 10 0 -h 3h 0 -(h+x) 3h 0.0035
GW 14 10 0 0 0 0 -h -h 0.0035
GW 15 10 0 -h -h 0 0 -2h 0.0035
GW 16 10 0 0 -2h 0 -h -3h 0.0035
GW 17 10 0 -h -3h 0 -(h+x) -3h 0.0035
GW 18 18 -s (R1+y/2+g/2) -4.5h -s y/2+g/2 -4.5h 0.0035
GW 19 18 -s -(R1-y/2+g/2) -4.5h -s y/2-g/2 -4.5h 0.0035
GW 22 18 -s (R2+y/2+g/2) -3.5h -s y/2+g/2 -3.5h 0.0035
GW 23 18 -s -(R2-y/2+g/2) -3.5h -s y/2-g/2 -3.5h 0.0035
GW 30 18 -s (R3+y/2+g/2) -2.5h -s y/2+g/2 -2.5h 0.0035
GW 31 18 -s -(R3-y/2+g/2) -2.5h -s y/2-g/2 -2.5h 0.0035
GW 38 18 -s (R4+y/2+g/2) -1.5h -s y/2+g/2 -1.5h 0.0035
GW 39 18 -s -(R4-y/2+g/2) -1.5h -s y/2-g/2 -1.5h 0.0035
GW 46 18 -s (R5+y/2+g/2) -0.5h -s y/2+g/2 -0.5h 0.0035
GW 47 18 -s -(R5-y/2+g/2) -0.5h -s y/2-g/2 -0.5h 0.0035
GW 52 18 -s (R5+y/2+g/2) 0.5h -s y/2+g/2 0.5h 0.0035
GW 53 18 -s -(R5-y/2+g/2) 0.5h -s y/2-g/2 0.5h 0.0035
GW 60 18 -s (R4+y/2+g/2) 1.5h -s y/2+g/2 1.5h 0.0035
GW 61 18 -s -(R4-y/2+g/2) 1.5h -s y/2-g/2 1.5h 0.0035
GW 68 18 -s (R3+y/2+g/2) 2.5h -s y/2+g/2 2.5h 0.0035
GW 69 18 -s -(R3-y/2+g/2) 2.5h -s y/2-g/2 2.5h 0.0035
GW 76 18 -s (R2+y/2+g/2) 3.5h -s y/2+g/2 3.5h 0.0035
GW 77 18 -s -(R2-y/2+g/2) 3.5h -s y/2-g/2 3.5h 0.0035
GW 80 18 -s (R1+y/2+g/2) 4.5h -s y/2+g/2 4.5h 0.0035
GW 81 18 -s -(R1-y/2+g/2) 4.5h -s y/2-g/2 4.5h 0.0035
GE 0
LD 5 0 0 0 24900000
GN -1
EK
EX 0 1 3 00 1 0
FR 0 0 0 0 585 0
EN

----------------------------------------------------------------------

The GH10 design has 10 pair of collinear rod reflectors and has a peak raw gain of 15.26dBi at 520 Mhz and 15.67dBi at 610 Mhz.

The construction of the Gh10 is somewhat complicated due to the 10 pair collinear reflectors,
so I had a quick look at a GH4 2nd Generation design, which has only 4 pair of rod reflectors.

This GH4 design has not been completely optimized, but applying the same design process as the GH10
currently gives 13.85dBi at 520 Mhz and 14dbi at 610 Mhz.

The max difference between the GH10 and GH4 designs is a difference of 1.67dBi at 610 Mhz and 1.41dBi at 520 Mhz,
so the added complication of 6 additional pair of rod reflectors, may not be worth the effort for most folks.

Here is the 4nec2 results for the GH4 design..

AGT TestResults

http://i258.photobucket.com/albums/hh262/autofils/GH42ndGENAGTTestResults.gif


GH4 2nd_GEN SWR Plot

http://i258.photobucket.com/albums/hh262/autofils/GH42ndGEN-Swr.gif


GH4 2nd_GEN RawGain Plot

http://i258.photobucket.com/albums/hh262/autofils/GH42ndGEN-RawGain.gif

GH4 2nd_GEN SY Variable nec File


All dimensions are stated in the nec file and are in meters.
The diameter of the array and rod reflectors that was modeled was 7mm.
(For construction, element diameter range should be within 1/4 to 3/8 inches.)
--------------------------------------------------------------------

CM SBGH 2nd Gen GH4 Collinear Rods
CE
SY y=0.095 'FeedGap spacing
SY x=0.110 'Length of Array Horizontal Stub
SY h=0.16 'Array Diagonal length = [Sqrt(2) x h] = 0.226
SY s=0.100 'Reflector Spacing
SY g=0.05 'Reflector pair Gap Spacing
SY R1=0.31 'Collinear reflector lengths
SY R2=0.29
GW 1 7 0 0 0 0 y 0 0.00349
GW 2 10 0 y 0 0 y+h h 0.0035
GW 3 10 0 y+h h 0 y 2h 0.0035
GW 4 10 0 y 2h 0 y+h 3h 0.0035
GW 5 10 0 y+h 3h 0 y+h+x 3h 0.0035
GW 6 10 0 y 0 0 y+h -h 0.0035
GW 7 10 0 y+h -h 0 y -2h 0.0035
GW 8 10 0 y -2h 0 y+h -3h 0.0035
GW 9 10 0 y+h -3h 0 y+h+x -3h 0.0035
GW 10 10 0 0 0 0 -h h 0.0035
GW 11 10 0 -h h 0 0 2h 0.0035
GW 12 10 0 0 2h 0 -h 3h 0.0035
GW 13 10 0 -h 3h 0 -(h+x) 3h 0.0035
GW 14 10 0 0 0 0 -h -h 0.0035
GW 15 10 0 -h -h 0 0 -2h 0.0035
GW 16 10 0 0 -2h 0 -h -3h 0.0035
GW 17 10 0 -h -3h 0 -(h+x) -3h 0.0035
GW 20 18 -s (R1+y/2+g/2) -3h -s y/2+g/2 -3h 0.0035
GW 21 18 -s -(R1-y/2+g/2) -3h -s y/2-g/2 -3h 0.0035
GW 24 18 -s (R2+y/2+g/2) -h -s y/2+g/2 -h 0.0035
GW 25 18 -s -(R2-y/2+g/2) -h -s y/2-g/2 -h 0.0035
GW 26 18 -s (R2+y/2+g/2) h -s y/2+g/2 h 0.0035
GW 27 18 -s -(R2-y/2+g/2) h -s y/2-g/2 h 0.0035
GW 30 18 -s (R1+y/2+g/2) 3h -s y/2+g/2 3h 0.0035
GW 31 18 -s -(R1-y/2+g/2) 3h -s y/2-g/2 3h 0.0035
GE 0
LD 5 0 0 0 24900000
GN -1
EK
EX 0 1 4 00 1 0
FR 0 0 0 0 585 0
EN


-------------------------------------------------------------------------

Have fun :p

Here are the Net gain plots for the 2nd_Generation collinear rod reflector designs of GH4 and GH10.

You will note that the GH4 is very similar to the SBGH GPLv3 design, and the GH10 is similar to the DBGH GPLv3 design.

http://i258.photobucket.com/albums/hh262/autofils/NetGainGH4_GH10.gif

You can customize the frequency response within the post 09 UHF bandwidth of 470 to 700 Mhz to better suit your local conditions.
Simply scale all model variables except the array feedgap (y) and the reflector gap (g) by the factor [f2/f1]; where:

Edit - Correction re scale factor
f2 = existing Freq peak
f1 = new shifted Freq peak
For GH10 the highest existing peak gain occurs at 610Mhz.

If you wanted to shift the response down by 30 Mhz from the peak at 610 Mhz, the scale factor= 610/(610-30) =610/580 = 1.05, and the new peak should be at 580 Mhz

If you wanted to shift the response up by 30 Mhz from the peak at 610 Mhz, the scale factor= 610/(610+30) =610/640 = 0.953, and the new peak should be at 640 Mhz.

I hope this edited explanation clarifies the scaling factor for customizing the frequency response.
I have also added the Net gain plot showing freq along the x-axis. This will be more helpful than channel number.



Using 4nec2 v5.7.3, simply change the variables under the Symbols tab in the NEC editor (new) Ctrl+F4.
Verify that the AGT test result is still close to the original and then run 4nec2 to inspect your new design.


The mid frequency point for the post 09 UHF band lower and upper channels are:
Ch 14 = 473 Mhz
Ch 50 = 689 Mhz

If you build a 2nd generation GH, please post your GH design and reception results by channel.
Also please cross-reference your reception report to the TVfool.com reception prediction for your location.
Here is the link for TVfool.com.
http://www.tvfool.com/

I would guess that the GH4 will be good for Rx(dBm) of down to -95 dBm and GH10 for Rx(dBm) down to -100dBm, but reception reports would provide the definitive answer.

...thanks
Autofils

NetGain (x-axis = freq)

http://i258.photobucket.com/albums/hh262/autofils/NetGainGH2nd_genvsfreq.gif

As has been my custom to compare antenna designs by Net Gain parameters, here are the Net Gain plots showing an overall summary of the current 2nd Generation SBGH Designs that have been posted on this forum.

======================================================
For the maximum antenna gain and outdoor install, here are the choices:
======================================================

1. GH Curved_Mesh Screen - highest gain and widest bandwidth

2. GH10 Collinear Rod Reflector
This design has slightly lower gain and smaller bandwidth, so there are two versions.
- GH10 UHF-Lo (Peak gain for Channels 14-34)
- GH10 UHF-Mid (Peak gain for Channels 20-42)

Overall max dimensions: (WxHxD) inches
GH Cm Scr ................ 43x60x5.5
GH10 UHF-Lo ............ 45x63x4
GH10 UHF-Hi ............. 41x58x4

================================
Smaller Antenna Size (suitable for Attic)
================================
There are two versions: GH4 and GH4_Array-Only

Overall dimensions (inches):
GH4 ................... 27x38 x4
Array-Only .......... 24x38 --

Net Gain Summary

http://i258.photobucket.com/albums/hh262/autofils/GHNetGainCMandGH-Lo.jpg

http://i258.photobucket.com/albums/hh262/autofils/GHNetGainCMandGH-Mid.jpg

Links to 2nd Generation SBGH Designs
============================
Here are the links for the design info for the Curved-Mesh Screen; GH10 and GH4 designs:

Link for GH10 design:
http://www.digitalhome.ca/forum/showpost.php?p=776769&postcount=106

Link for GH4 design:
http://www.digitalhome.ca/forum/showpost.php?p=776930&postcount=107

Link for 300ohm's CurvedMesh Screen design:
http://www.digitalhome.ca/forum/showpost.php?p=780579&postcount=191

What is the difference between the 2 versions?

What is the difference between the 2 versions?

Gen2 is optimized for higher gain at the lower end of the UHF channels, but the gain falls off rapidly above around channel 42. It seems a lot of people arent going to have to worry about channels above about 42, so its popular.

Gen1 is optimized for the whole new UHF range, channels 14 to 51. Its gain is lower on the lower UHF channels than Gen2, but is still a very good performer for those channels. Above channel 42, the Gen1 has superior gain. Gen1 is also significantly smaller in size than the Gen2 antenna.