Hmm, just knocking the top and bottom pairs of uhf reflectors off the GH6 above, making it an unoptimized GH4, looks pretty darn good, and the uhf net gain very close to the GH4 optimized, vhf-hi about the same as above. A DBGH of it would be about 75 inches tall.
"Top Hat" GH with NARODs for VHF-HI: Major GH Improvement
this is a modification of the JED's GH10 (rev2),
with bent NARODs and 3 narod reflectors.
Chart:
![]()
Numerical gain data (VHF-hi):
Numerical gain data (UHF):
nec code
with bent NARODs and 3 narod reflectors.
Chart:
Numerical gain data (VHF-hi):
Code:
Ch 7 8 9 10 11 12 13
swr 1.63 1.69 2.24 2.2 1.84 1.34 1.17
Net Gain 9.06 9.33 8.9 8.78 8.83 8.81 8.29
Code:
Ch 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54
swr 1.22 1.27 1.36 1.45 1.52 1.55 1.47 1.38 1.35 1.35 1.36 1.37 1.38 1.38 1.39 1.39 1.4 1.4 1.41 1.42 1.44 1.48 1.53 1.57 1.6 1.62 1.64 1.67 1.69 1.72 1.75 1.78 1.8 1.83 1.85 1.87 1.91 1.95 2.01 2.09 2.18
Net Gain 13.59 13.9 14.14 14.29 14.35 14.33 14.43 14.59 14.65 14.66 14.65 14.61 14.58 14.55 14.51 14.5 14.49 14.47 14.43 14.38 14.27 14.13 14.05 14.1 14.27 14.46 14.61 14.76 14.88 14.99 15.11 15.22 15.32 15.41 15.47 15.47 15.39 15.18 14.86 14.39 13.74
Code:
CE
SY radius=0.003175
SY hat_rad=0.003175 '0.0010265
SY l1=0.381
SY g1=0.019
SY z1=0.037
SY l2=0.280
SY g2=0.009
SY z2=0.137
SY l3=0.556
SY g3=0.0055
SY z3=0.262
SY l4=0.511
SY g4=4e-3
SY z4=0.414
SY l5=0.270
SY g5=4e-3
SY z5=0.592
SY x=-0.081
SY a1=0.196
SY a2=0.192
SY a3=0.190
SY b=0.120
SY feed=0.0548348
SY a1ma2=a1-a2
SY a1pa2=a1+a2
SY a1ma2pa3=a1ma2+a3
SY a1pa2pa3=a1pa2+a3
SY n_l=0.449369
SY n_top_l=0.223443
SY n_b_l=(n_l - n_top_l)/2
SY n_z_sp=0.012
SY n_h=0.04795
SY n_b_z=a1pa2pa3*.7071+n_z_sp+hat_rad-radius
SY n_top_z=n_b_z+n_h
SY n_back=-0.25325
SY n_refl_size=0.404294
SY n_refl_z=0.367714
SY n_refl_size1=0.447082
GW 1 23 0 -feed 0 0 -feed-0.70711*a1 0.70711*a1 radius
GW 2 23 0 -feed-0.70711*a1 0.70711*a1 0 -feed-0.70711*a1ma2 0.70711*a1pa2 radius
GW 3 23 0 -feed-0.70711*a1ma2 0.70711*a1pa2 0 -feed-0.70711*a1ma2pa3 0.70711*a1pa2pa3 radius
GW 4 15 0 -feed-0.70711*a1ma2pa3 0.70711*a1pa2pa3 0 -feed-0.70711*a1ma2pa3-b 0.70711*a1pa2pa3 radius
GW 5 45 x g1 z1 x l1+g1 z1 radius
GW 6 33 x g2 z2 x l2+g2 z2 radius
GW 7 65 x g3 z3 x l3+g3 z3 radius
GW 8 61 x g4 z4 x l4+g4 z4 radius
GW 8 33 x g5 z5 x l5+g5 z5 radius
GW 13 7 0 -n_top_l n_top_z 0 -n_top_l n_b_z hat_rad
GW 14 13 0 -n_top_l n_b_z 0 -n_top_l-n_b_l n_b_z hat_rad
GX 20 010
GW 10 53 0 n_top_l n_top_z 0 -n_top_l n_top_z hat_rad
GW 15 95 n_back -n_refl_size n_refl_z n_back n_refl_size n_refl_z radius
GX 40 001
GW 100 13 0 -feed 0 0 feed 0 radius*.8675
GW 16 105 n_back -n_refl_size1 0 n_back n_refl_size1 0 radius
GE 0
LD 5 0 0 0 24900000
GN -1
EK
EX 0 100 7 0 1
FR 0 0 0 0 800 0
RP 0 60 73 1001 0 0 3 5
EN21 - 40 of 940 Posts
Never mind, its perfect as is. I did a longer frequency sweep and I see whats going on. It naturally falls that way if you want the entire vhf-high band (and SWR is starting to rise on the high channels now). Optimizing for the high channels would send the SWR sky high for the low channels. You have the best compromise for the entire vhf-high band as is now.
That would be great if you would.
The original GH6 has the reflector rods only as high as the stubs, making it more compact than JEDs models. A DBGH version of that would be about 70 inches tall, with a uhf gain of 16.5+ dbi and a vhf-hi gain of about 12 dbi net, if all goes well.The vhf-hi gain on all 3 of your models above has been very consistant. The GH10 actually has the lowest vhf-hi gain of the bunch.
A long time ago, it was determined the wider feed point in the 80 - 110 mm range gave a bit better gain on that model. Since the distance across one of my tees is 89mm, that makes a very convenient stop for the edge of the driven element. While maybe an even wider gap would give a tiny bit more gain, the tiny increase in gain isnt worth sacrificing the great benefit of that stop point. Its always a compromise, heh.
Ill need to do more work on the double bay version of the orig GH6 with top hat NARODs and 6 NAROD reflectors. So far, Ive only gotten it to peak at 11.59 dbi with a SWR of 2.23. Not an improvement in peak gain over what I originally had here on post #20: http://www.digitalhome.ca/forum/showthread.php?t=99907&page=2
I was hoping for more with the 2 extra NAROD reflectors because the single bay version looked so promising.
The law of marginal utility of NAROD reflectors kicking in ??
The gain and SWR curves are smoother though, and the channel 13 gain is up about a db.
I was hoping for more with the 2 extra NAROD reflectors because the single bay version looked so promising.
The law of marginal utility of NAROD reflectors kicking in ??
The gain and SWR curves are smoother though, and the channel 13 gain is up about a db.
300Ohm,300Ohm said:
Thanks for the link re the discussion on auto-seg. I have only quickly scanned from post #422 to 432, but I'm not at all sure, I can identify any clear consensus. It appears that there was agreement to use auto-segmentation, but I am left wondering if the original cause of different modeling results was clearly understood.
A modeler gives up control of his model to this auto-segmentation algorithm that Arie has coded for 4nec2. I'm from the old school, where you manually set the segmentation. Then as I said before, besides running an AGT test at the mid designed bandwidth freq, (or at the band limits, if required) you also run convergence tests by increasing the manually set segmentation to ensure there is no significant change in the gain/swr results if more segments are defined in your model. Now for TV UHF, you also run up against that wire diam /seg_len problem, so you do have to be careful and really understand what these tests do and what you are doing as well ... life is not always simple and blind accepance on automatic computer segmentation may have some unexpected consequences.
I would refer folks to the ARRL Antenna Book Chp 4 "Antenna Modeling & System Planing ( I have 21st edition). It discusses the Accuracy Tests for nec models. There are only two: The Convergence test and the Average gain test (AGT)
Here is an important quote from pg 4-16: Like the convergence test, the average gain test is a necessary but not a sufficient condition of model reliability. Pass both tests, however and you can be pretty well sure that your model represents reality.
For any modeler that posts on this forum, that does not understand this quote, I highly recommend that you beg, borrow or steal a copy of the ARRL Antenna Book and start reading. I don't really advise breaking the law
.... It should be available in just about any public library in North America.You should also read all 4 parts of "A Beginner's Guide to Modeling with NEC". Part 4 has good discussion on the convergence and AGT tests under the heading "Testing Models". These guides are available on Arie's site. http://home.ict.nl/~arivoors/
I hope this helps.
OK, 1 1/4 dbi, I exaggerated a bit,heh.
Yes, you do. Some of us are eagerly awaiting that, as well as your Rev 3 GH10 antennas... back to work!
21 - 40 of 940 Posts
