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GH with NARODs for VHF-HI & UHF

353555 Views 579 Replies 97 Participants Last post by  300ohm, 
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Success !!! I got the Vhf-Hi gain going the right way with the colinear rod reflector models and with more gain to boot ! (This does not apply to the mesh models, for obvious reasons.)

Using the basic original SBGH gen1 colinear rod plans (with 10ga elements, 3/8 inch reflectors), I placed additional 28 inch, 3/8 inch reflectors 10 inches behind the 28 inch 10 ga NARODs that are 1/2 inch above the stubs. Oddly, using a larger reflector than the driven element, typical in most TV antenna designs, decreased performance, as did a smaller reflector.

The effective bandwidth for Vhf-Hi is somewhat limited to about 4 channels. I tweaked for channels 10 to 13, so if channels 7 to 9 are needed, adjustments have to be made.

The use of the NARODs levels out and dips the gain curve similiar to the SBGH JED Gold Standard model, so the original SBGH gen1 model is so far the best to use in this case so as to not exacerbate the dip further.

VHF-HI

CH Raw Gain SWR
-- -------- -----
07 5.56 dBi 62.3 (7.93 dBi at 180 degrees)
08 6.27 dBi 23.0 (8.02 dBi at 180 degrees)
09 8.07 dBi 5.67
10 9.66 dBi 2.37
11 9.81 dBi 3.7
12 9.26 dBi 3.58
13 8.66 dBi 3.16

Channel 10 pattern :


3D Picture :


UHF Raw Gain Chart :


UHF SWR :


NEC file :

Code: 
CE
GW	30	15	0	1.73228346	0	0	6.73228346	5	0.05094856
GW	31	15	0	1.73228346	10	0	6.73228346	5	0.05094856
GW	32	15	0	1.73228346	10	0	6.73228346	15	0.05094856
GW	34	15	0	-1.7322835	0	0	-6.7322835	5	0.05094856
GW	35	15	0	-1.7322835	10	0	-6.7322835	5	0.05094856
GW	36	15	0	-1.7322835	10	0	-6.7322835	15	0.05094856
GW	38	15	0	1.73228346	0	0	6.73228346	-5	0.05094856
GW	39	15	0	1.73228346	-10	0	6.73228346	-5	0.05094856
GW	40	15	0	1.73228346	-10	0	6.73228346	-15	0.05094856
GW	42	15	0	-1.7322835	0	0	-6.7322835	-5	0.05094856
GW	43	15	0	-1.7322835	-10	0	-6.7322835	-5	0.05094856
GW	44	15	0	-1.7322835	-10	0	-6.7322835	-15	0.05094856
GW	79	25	-4.1338583	-0.3937008	15	-4.1338583	-12.440945	15	0.1875
GW	80	25	-4.1338583	0.39370079	15	-4.1338583	12.4409449	15	0.1875
GW	81	25	-4.1338583	0.39370079	-15	-4.1338583	12.4409449	-15	0.1875
GW	82	25	-4.1338583	-0.3937008	-15	-4.1338583	-12.440945	-15	0.1875
GW	84	25	-4.1338583	0.39370079	2.5	-4.1338583	12.007874	2.5	0.1875
GW	85	25	-4.1338583	-0.3937008	2.5	-4.1338583	-12.007874	2.5	0.1875
GW	86	25	-4.1338583	0.39370079	7.5	-4.1338583	12.4409449	7.5	0.1875
GW	87	25	-4.1338583	-0.3937008	7.5	-4.1338583	-12.440945	7.5	0.1875
GW	88	25	-4.1338583	0.39370079	-2.5	-4.1338583	12.007874	-2.5	0.1875
GW	89	25	-4.1338583	-0.3937008	-2.5	-4.1338583	-12.007874	-2.5	0.1875
GW	90	25	-4.1338583	0.39370079	-7.5	-4.1338583	12.4409449	-7.5	0.1875
GW	91	25	-4.1338583	-0.3937008	-7.5	-4.1338583	-12.440945	-7.5	0.1875
GW	103	13	0	6.73228346	15	0	12.3228346	15	0.05094856
GW	104	13	0	-6.7322835	15	0	-12.322835	15	0.05094856
GW	106	13	0	6.73228346	-15	0	12.3228346	-15	0.05094856
GW	107	13	0	-6.7322835	-15	0	-12.322835	-15	0.05094856
GW	138	29	0	-14	15.5	0	0	15.5	0.0511811
GW	142	29	0	0	15.5	0	14	15.5	0.0511811
GW	139	29	0	-14	-15.5	0	0	-15.5	0.0511811
GW	143	29	0	0	-15.5	0	14	-15.5	0.0511811
GW	144	23	-10	14	15.5	-10	-14	15.5	0.1875
GW	145	23	-10	14	-15.5	-10	-14	-15.5	0.1875
GW	146	3	0	-1.7322835	0	0	1.73228346	0	0.01
GS	0	0	0.0254		' All in in.
GE	0
EK
EX	0	146	2	0	1	0
GN	-1
FR	0	38	0	0	473	6
RP 0 1 10 1510 90. 0. 0. 20. 0. 0.
See development background in this thread: http://www.digitalhome.ca/forum/showthread.php?t=98619
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S
Hello, 300ohm,
I am a new member and but I have been going over the postings for the last year. I was just wondering if you have made any progress on the DBGH GH10 CURVED MESH plans since the middle of the year and or have you abandoned that concept. I am also curious about the spacing of the 2 bays. Do you think that the NAROD concept will work for the curved mesh antenna?
By the way, wonderful research!
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T
Accordng to tvfool.com, all of my Channels are between 25.3 miles and 26.3 miles away and between 288° and 291° from True North, except one really close one, Channel 15, which is at 104° from True North and 9.3 miles away.

In respect to your question, Channel 8 is at -39dBm, while Channel 13 is at -38.7dBm. They are both 25.3 miles away and at 291° from True North.
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In respect to your question, Channel 8 is at -39dBm, while Channel 13 is at -38.7dBm. They are both 25.3 miles away and at 291° from True North.
Click to expand...
Since theyre both strong, the middle choice would suit you, NAROD and NAROD lengths at 30.25 inches and NAROD to NAROD reflectors spacing of 11.5 inches.

You should be able to pick up channel 15 on the back side no problem.
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T
11.5 inches is center to center spacing between the NAROD and NAROD reflectors, correct?
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I was just wondering if you have made any progress on the DBGH GH10 CURVED MESH plans since the middle of the year and or have you abandoned that concept.
Click to expand...
Not really, Im using the SBGH GH10 Curved Mesh as my garage antenna.The SBGH GH10 Curved Mesh is a big antenna at 4 ft wide by 5 ft high. The DBGH GH10 Curved Mesh would be about 4 ft wide by 11 ft high and overkill for me.

I am also curious about the spacing of the 2 bays.
Click to expand...
That follows my rule of thumb for all DBGHs, 2 times the wavelength of the desired peaking channel minus 2 %, feedpoint to feedpoint spacing. For the 89mm feedpoint gap, a 2 inch (50mm) phasing line gap, 1 inch (25mm) in front of the elements works fine. Keep the phasing lines perfectly parallel, using plastic spacers if necessary.

Do you think that the NAROD concept will work for the curved mesh antenna?
Click to expand...
Nope, unfortunately the mesh messes up the gain and gain direction. I havent found a way around that yet and still perserve the great uhf gain.
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11.5 inches is center to center spacing between the NAROD and NAROD reflectors, correct?
Click to expand...
Yes, thats correct.
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T
I'm planning on building a SBGH 6 using effects build as a guide, except I'm going to have to find a way to add the NARODs and NAROD reflectors to his build.

My SBGH Build & Parts Lis-effects
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J
300ohm said:
For the channel range peaking at channels 8,9,10
and a good VHF-HI overall compromise, the NAROD and NAROD reflector
length is 30.25 inches and the NAROD to NAROD reflector distance is
11.5 inches. As you can see from the 3 different models (VHF-HI low,
middle and high range) it doesnt take much to distort the gain range.
Click to expand...
Hi 300ohm,

I have not tested your nec file much, but at first sight it looks good
on VHF-Hi. I did not try to increase the segmentation to look for
convergence. Here are the AGT adjusted values that I computed:
Code: 
 freq[MHz]        SWR    RawGain    NetGain        F/B
       170    4.92268     8.2644    5.75665       1.31
       176    2.84224    8.74569    7.61121       5.62
       182    2.56054    11.5831    10.6567       8.75
       188    3.33013    11.5018    10.0169      21.06
       194    3.00771    11.1019    9.84691      18.93
       200    2.53878    10.6902       9.78      11.36
       206    2.35895    10.3178    9.54153       7.92
       212    2.58387    9.99473    9.05099       5.71
It also looks good on UHF:
Code: 
 freq[MHz]        SWR    RawGain    NetGain        F/B
       473    5.68674    15.0137    12.0787      12.61
       479    5.01432    15.2936    12.7326      12.98
       485    4.36631    15.5257     13.354      13.43
       491    3.77206    15.7001    13.9123      13.91
       497    3.25089    15.8462    14.4172      14.44
       503    2.81138    15.9439     14.832      14.95
       509     2.4543    16.0229    15.1756      15.42
       515    2.17549     16.063     15.423       15.8
       521    1.96812    16.0641    15.5756      16.04
       527    1.82396    16.0259    15.6395      16.11
       533    1.73304    15.9477    15.6235      16.03
       539    1.68275    15.8084    15.5176       15.8
       545    1.65832    15.6067    15.3319      15.52
       551    1.64678    15.3524     15.085      15.36
       557    1.64067    15.0864    14.8229      15.47
       563    1.63787    14.8499    14.5882      15.93
       569    1.63866    14.6637    14.4016      16.73
       575    1.64508    14.5284    14.2621      17.81
       581    1.66103    14.4548    14.1782      19.16
       587    1.69111    14.4429    14.1465      20.69
       593    1.73773    14.4927    14.1653      22.17
       599    1.79808    14.6031    14.2346      23.11
       605    1.86645    14.7538    14.3376      22.98
       611    1.93462    14.9437    14.4792      21.91
       617    1.99529    15.1527    14.6446      20.44
       623    2.04268    15.3708    14.8282      18.95
       629    2.07319    15.5787    15.0139      17.57
       635    2.08147    15.7778    15.2069      16.34
       641    2.06526    15.9689    15.4099       15.3
       647    2.02027    16.1227    15.5965      14.41
       653    1.94403    16.2583     15.787       13.7
       659    1.83661    16.3643    15.9691      13.13
       665    1.70051    16.4399    16.1374      12.67
       671    1.54057    16.5137    16.3125      12.31
       677    1.36043    16.5862    16.4837      12.01
       683    1.16936    16.6576     16.631      11.74
       689    1.06377     16.729    16.7248       11.5
       695    1.31742    16.7914    16.7092      11.27
Thanks,
--John
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Here are the AGT adjusted values that I computed:
Click to expand...
Yep, looks like about the same figures at slightly different frequencies. Autofils and I generally use the middle of the channel. In VHF though its good to see the tops and the bottoms of the channels too, for example the YA-1713 channel 13 drop off, heh.
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I'm planning on building a SBGH 6 using effects build as a guide, except I'm going to have to find a way to add the NARODs and NAROD reflectors to his build.
Click to expand...
Yeah, thats a nice build, almost identical to mlords builds.

For the NAROD to stub holders with #6 wire, you could use small thin stiff pieces of plastic (vynil siding cut to about 1 inch by 1/2 inches pieces comes to mind) with holes drilled in them at 1/2 inch on center, drilled just slightly smaller than the wire diameter (9/64ths drill bit ?) so that they can still be slipped on with a little force. I would say about 4 per NAROD would hold nicely. A dab of Plumbers Goop (basically thick model airplane cement) could be used to permanently hold them, if need be.

For the NAROD reflectors, additional tees and 1/2 inch pvc pieces could be used. My slip on tees would work nicely and allow you to adjust the NAROD reflectors until they are perfectly parallel to the NARODs. Then a small #4 screw can hold the tees etc in place.
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T
Im a bit confused. Which plans are the best to use? I am looking at this thread, but see 2-3 different kinds of antennas posted in the pictures. I like the look of the curved antenna, is this a good one?

http://www.digitalhome.ca/forum/showthread.php?t=95898
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P
I thought the Oroginsl DBGH had only 1 set of coliner reflectors at the stack joint insread of the 2 shown, 11 pair total. I 've got an unfinished carboard & coathanger project with 11 pair in place that I plan to convert.
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C
Ganging two SBGHs Horizontally

What would happen if you ganged two SBGHs horizontally with the mesh reflectors touching? Would it result in any VHF-high gain? What would happen to UHF gain?

I am asking since this is how the CM4228 achieves VHF-high gain.

The following is a quote from HDTVprimer:
"This antenna (CM4228) is advertised solely as a UHF antenna. But, as many people have discovered, it has strong gain for VHF-high, especially channel 9-13. What gives it this ability is the continuous screen. Other 8-bays have a reflector that is not continuous across the right and left halves. Those antennas have little usefulness for VHF channels.
The continuous screen is not simply a reflector for these channels, but rather it becomes the primary radiating element. As a result, radiation out the back is very strong, nearly bi-directional for some channels."

If there is the possibily of VHF-high gain, is anyone interested in modelling it?
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What would happen if you ganged two SBGHs horizontally with the mesh reflectors touching? Would it result in any VHF-high gain? What would happen to UHF gain?

I am asking since this is how the CM4228 achieves VHF-high gain.
Click to expand...
Nope, the GH behaves differently than the bowties. The NARODs are the only way found so far to give positive VHF-Hi net gain.
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H
Using 4nec2, I calculated performance charts for 300ohm's DBGH (with 28 NARODs):
http://imageevent.com/holl_ands/grayhoverman

I used the Combo Hi-VHF & UHF capability to investigate what happens if insulated
AWG10 wire is used instead of Bare wire....it wasn't very pretty....(NARODS were left Bare).

FYI: In NEC, fol. Loading card adds 24 mil PVC coating on top of AWG10 for each GW#:
LD 7 GW# 0 0 4.5 0.075
Repeat as necessary for all affected wires....
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M
PoppaDigital said:
I thought the Oroginsl DBGH had only 1 set of coliner reflectors at the stack joint insread of the 2 shown, 11 pair total.
Click to expand...
That is correct. The link tvmonkey posted does not show an original DBGH.

-ml
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holl_ands,

I need to clarify my terminology for you. The NARODS are only the 4 wires directly above the stubs. (I have them split into 2 pieces each on the model to investate the effects of slanting them). The term NAROD stands for Not A Reflector Or Director. I coined the term because I dont know what else to call them. NARODS are interesting little animals. They are having some kind of a drastic capacitance or current effect on the GH driven elements.

The rest of the wires are reflectors or driven elements. (the wires 10 or so inches behind the NARODs could be called NAROD reflectors). So in the model you link to, there are only 4 NARODs and 4 NAROD reflectors, installed on DBGH gen 1 co-linear rod 12 pair model.

The vhf-hi bandwidth is narrow, hence the need for 3 different models. And if youll notice, the max vhf-hi forward gain can flip direction 180 degrees on some of the off channels.

From my actual builds in the past (other designs) Ive always noticed that bare wire performs better, so Im not surprised by your results. Bare wire also gives the antenna more of an antenna look, instead of a bunch of (different colored in my case) house wire thrown together, heh.
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I have added vertical wires (alligator clips with 18 gauge) to NARODS (29.5"). This makes a loop around the driven element. It seems to reduce analog ghosts on the weak Ch. (NM -8). I'm running gen. 2 GH fractal with Al.-foil reflector (15") and NARODS reflectors at 11.5" spacing.
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D
holl_hands, you wrote:
LD 7 GW# 0 0 4.5 0.075

Is your nec file mistakenly back in meters?
See the GS instruction, if you have any.
The nec files of 300ohms earlier are in inches and show a GS scale of 0.0254.

I set a DB4 model to add the
LD 7 0 0 0 4.5 0.075
(GW# of 0 means all wires)
and when I clicked on a wire, the popup box showed me I had 75mm of coating!

So be sure you have the right units.
In a metric file, (no GS scale), I have
LD 7 0 0 0 4.5 0.001905

that is 1.905 mm outer radius.
The simulation show no noticeable change. Coating has no visible effect.
Sorry.
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The simulation show no noticeable change. Coating has no visible effect.
Click to expand...
Im still gonna use bare wire, heh.
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