I'm a new member and this is my first post, but I've been following the GH and modeling/analysis discussions here for some time... so let me say "Thank you!" to everyone for being so willing to share your knowledge and efforts. And special thanks to nikiml; your site has been of tremendous help.

Here's my situation: I have available an assortment of digital and low-power analog stations with noise margins ranging from 10.5 to 46.6 dB (10' open-air elevation -- but the antenna's in an attic). All are UHF except for one on channel 12 at 42.6 dB.

As a first test, I cobbled together a crude GH0n3 (because it was simple and quick to construct) using 1/2" copper tape on styrofoam insulation board. It was able to snag all hoped-for stations, though 12 didn't have a lot of signal to spare. Since I want to allow for atmospheric variances, snow on the roof, etc., my actual build will be a GH6n3 (which has the highest channel 12 gain of the versions I studied).

Additionally, I've been tinkering with the design in an attempt to maximize channel 12 gain without unduly compromising the UHF band. At this point I seem to have a model that boosts 12 by about 2 dB over a GH6n3 with less than a half decibel damage to the UHF band, worst case. At this point it's a bit unwieldy -- the center reflector's over two meters wide for example, and the top-hat NAROD spacing looks disturbingly tight -- but I'm hopeful such things can be tweaked.

Before I spend any more time on it though, I'd really like someone with a practiced eye to take a look. I'm new to 4nec2 you see, plus it's been a LONG time since I earned my First Class license and most of my antenna knowledge is rusty from lack of use. The output seems reasonable, but I could easily have overlooked something or misused the program in some way. So, I'd love a sanity check just to make sure I'm on the right track.

Here's the nec file (this is with copper versus T6 aluminum, and #4 wire for the driven element and top hats, by the way):

Code:

```
CM CH12 OPTIMIZED COPPER #4 DRIVEN AND NARODS
CM Based on GH6n3 optimized by nikiml
CE
SY radius=0.003175
SY narod_surf_spacing=7.884e-3
SY narod_spacing=6.76e-3
SY feed=0.05417 '0.02, 0.07
SY b=0.1247179 '0.075, 0.25
SY a1=0.1518191 '0.07, 0.22
SY _G3=0.05551477 '0.006, 0.1
SY a2=a1+feed-_G3 'this is to avoid self intersection since _G3 is to be > radius+2.5mm
SY a3=0.123689 '0.07, 0.22
SY x=-0.08082828 '-0.06, -0.1
SY g1=0.01437272 '0.002, 0.045
SY g2=0.045
SY g3=0.04499394
SY l1=0.3186459 '0.1, 0.6
SY l2=0.3773999 '0.1, 0.65
SY l3=0.6086331 '0.1, 0.65
SY n_h=0.103995 '0.05, 0.14
SY n_f_dx=0
SY n_top_dy=-0.03689449 '-0.06, 0.04
SY n_b_taper=0
SY n_top=_G3+a3+n_top_dy- n_b_taper/2 'hat head size
SY n_f=x + n_f_dx 'so the hat does not tilt behind the reflectors
SY narod_top = a1+a2+a3+narod_spacing+n_h 'want to put 3 reflectors between z=very_small and z=narod_top +/- very_small, 1 reflectors around narod_top and 1 above it
SY dz3=0.1106235 '0.017, 0.15
SY above_below=-2
SY sign = abs(above_below)/above_below 'may fail at 0
SY z3 = sign*dz3+narod_top
SY dz = z3/5
SY dz1=1.116735 '0.2, 2
SY z1 = (1+(dz1-1))*dz
SY dz2=1.020749 '0.2, 2
SY z2 = (3+(dz2-1))*dz
SY ay1=feed+a1
SY ay2=feed+a1-a2
SY ay3=feed+a1-a2+a3
SY ay4=feed+a1-a2+a3+b
SY az2=a1+a2
SY az3=a1+a2+a3
SY n_b_z=az3+narod_spacing
SY n_b_y1=n_top+n_b_taper
SY n_b_y2=n_b_y1+b
SY n_z_coef=0.792873 '0.5, 1.4
SY n_zsz=0.361459 '0.3, 0.55
SY n_0sz=1.046914 '0.3, 0.6
SY n_x_diff=0.256792 '0.15, 0.4
SY n_x = x-n_x_diff
SY n_z = narod_top*n_z_coef
GW 1 11 0 feed 0 0 ay1 a1 #4 '#00f
GW 2 11 0 ay1 a1 0 ay2 az2 #4 '#00f
GW 3 9 0 ay2 az2 0 ay3 az3 #4 '#00f
GW 4 7 0 ay3 az3 0 ay4 az3 #4 '#00f
GW 5 17 x g1 z1 x l1+g1 z1 radius '#0f0
GW 6 20 x g2 z2 x l2+g2 z2 radius '#0f0
GW 7 32 x g3 z3 x l3+g3 z3 radius '#0f0
GW 11 8 n_f n_top n_b_z+n_h 0 n_b_y1 n_b_z #4 '#000
GW 12 7 0 n_b_y1 n_b_z 0 n_b_y2 n_b_z #4 '#000
GX 20 010
GW 13 15 n_f -n_top n_b_z+n_h n_f n_top n_b_z+n_h #4 '#000
GW 15 43 n_x -n_zsz n_z n_x n_zsz n_z radius '#D00
GX 40 001
GW 16 56 n_x -n_0sz 0 n_x n_0sz 0 radius '#D00
GW 100 9 0 -feed 0 0 feed 0 radius*.8675 '#f40
GE 0
LD 5 0 0 0 58000000
GN -1
EK
EX 0 100 5 0 1 0 0
FR 0 0 0 0 800 0
EN
```

Here are the SWR graphs, again plotted against a reference:

As you can see, it's surprisingly good (well, to me as a newbie modeler anyway), which is why I assume I've done something wrong or overlooked something.

Here's a render as a visual aid; you'll see what I mean about the wide center reflector and tight top hat spacing:

I pretty much have no idea what I'm doing (grin), so I'm open to any and all input.

Thanks,

Rick