The Jeffrika7b in Simulation
The Jeffrika7 is an ATSC 3.0 television antenna of my own
design. It is "open source" and free for anyone to copy, build, or modify.
This is the "Jeffrika7b" variant, that was modeled with 1" support bolts at
50mm separation, allowing it to be built out of commonly available parts with
minimal fabrication steps. This antenna was based on my manually designed
Jeffrika6 "Folded NARODS" antenna, which was in turn based on a modified Gray
Hoverman antenna. The optimization into the Jeffrika7b form was carried out by
a custom simulated annealing program I wrote ("searcher.7.c") specifically for
the task.
The Jeffrika7b is designed for a bi-directional, horizontally polarized
reception patern over the two ATSC bands, VHF 7-13 (174-216 MHz) and UHF 14-36
(470-608 MHz), with an impedance of around 300 Ohms. The "score" that I used
for optimization was the average of the minimum and maximum Net-Gain in dBi in
each band, combined into a single weighted average. Net-Gain was used as the
score because it takes the VSWR into account. The antenna has a (predicted)
average net gain of 6.31 dBi across the VHF band, 10.96 dBi across the UHF
band. The average VSWR is 3.02 for VHF, and 2.48 for UHF, but is below 2.0 for
most of the channels. By this metric, it "scores" a 9.88.
I used Xnec2c to compare the net gains between four
different antennas: the Jeffrika7b; Jeffrika6; the Modified Gray Hoverman with
NAROD Hat that I built but did not design; and the Gray Hoverman UHF model that
ships with Xnec2c, minus the reflector patch. The Jeffrika7b has significant
gain over the other models across both the VHF and UHF bands. The
original Gray Hoverman design was only meant for UHF reception, so it is not
surprising that it shows no gain in the VHF band. The simulation data for the
'Narod Hoverman' that was supposed to pull in the VHF band shows a
clear problem there. While the max gain for channels 7-13 is reasonable and
the net gain on channels 11-13 is fine, the VSWR for channels 7-10 is out of
control. The very high VSWR at those frequencies leads to a non-existent net
gain for channels 7-10. No wonder I couldn't get VHF channel 9 to come in with
that antenna!
The radiation patterns in from the simulation show that the jeffrika7b is bidirectional. As expected, the higher gain in the UHF band leads to a narrower beam width. Xnec2c doesn't let me print out polar plot, or give me an easy beam width measurement, but I believe the -3dB beam width is about 54 degrees for UHF and 76 degrees for VHF if I'm using the software correctly. That seems to work out pretty well for the spread on the stations that are near me, which are mostly grouped NE and S from my location.
The Jeffrika.7b.nec file for use with Xnec2c is available for download, and is listed below. You might need to change some Xnec2c specific things to get it to load into other NEC software. For example, it uses the Xnec2c specific ZO card to set the TX Line Impedence in the frequency plots, Xnec2c's multiple FR cards, and Xnec2c's single quote comment character. Other than that, is should load up into any NEC software, of terrestrial or otherworldly origin.
' Comments
CM *** Jeffrika7 ATSC 3.0 Antenna ***
CM Copyright 2023 J.Jahr
CM This design is Open Source and free for anyone to use.
CM This is the Jeffrika7b variant, with the cost reduced bracket width,
CM and modeled with 1" bracket support bolts.
CM It is a bidirectional antenna, and covers VHF 7-13, UHF 14-36.
CM (This file was created by searcher.j7.c on Jun 29, 2023)
CM Score=9.876461
CE
' UHF
' uhf segment 1 length = 200mm 7+7/8"
' uhf segment 1 height = 58mm 2+5/16"
GW 1 10 0.000000e+00 0.000000e+00 0.000000e+00 1.917520e-01 0.000000e+00 5.840200e-02 1.650000e-03
' uhf segment 2 length = 335mm 13+3/16"
' uhf segment 2 height = 333mm 13+1/8"
GW 2 16 1.917520e-01 0.000000e+00 5.840200e-02 0.000000e+00 0.000000e+00 3.327030e-01 1.650000e-03
' uhf segment 3 length = 202mm 7+15/16"
' uhf segment 3 height = 420mm 16+1/2"
GW 3 10 0.000000e+00 0.000000e+00 3.327030e-01 1.822270e-01 0.000000e+00 4.196800e-01 1.650000e-03
' uhf segment 4 length = 86mm 3+3/8"
' uhf segment 4 height = 420mm 16+1/2"
GW 4 4 1.822270e-01 0.000000e+00 4.196800e-01 2.678070e-01 0.000000e+00 4.196800e-01 1.650000e-03
' UHF side LOA 1645mm 64+3/4"
' VHF narod top height = 432mm 17"
' Top Segment 10 length to wrap 293mm 11+1/2"
GW 10 14 -2.500000e-02 0.000000e+00 4.323800e-01 2.678070e-01 0.000000e+00 4.323800e-01 1.650000e-03
GA 11 15 1.270000e-02 9.000000e+01 -9.000000e+01 1.650000e-03 0 0 0
GM 0 0 0 0 0 2.678070e-01 0 4.196800e-01 11
' Tail Segment after wrap 12 73mm 2+7/8"
GW 12 3 2.678070e-01 0.000000e+00 4.069800e-01 1.949270e-01 0.000000e+00 4.069800e-01 1.650000e-03
' VHF narod length 406mm 15+15/16" with wraparound
' VHF narod LOA 811mm 31+15/16"
' Symmetry
GM 0 0 0 0 0 2.500000e-02 0 0 1
GX 0 101 0 0 0 0 0 0 0
' Support bolts
' Narod Support
' bolt A 25mm 1"
GW 30 1 -2.500000e-02 0.000000e+00 4.323800e-01 -2.500000e-02 -2.540000e-02 4.323800e-01 2.413000e-03
' bolt B 25mm 1"
GW 31 1 2.500000e-02 0.000000e+00 4.323800e-01 2.500000e-02 -2.540000e-02 4.323800e-01 2.413000e-03
' bolt A 25mm 1"
GW 32 1 -2.500000e-02 0.000000e+00 -4.323800e-01 -2.500000e-02 -2.540000e-02 -4.323800e-01 2.413000e-03
' bolt B 25mm 1"
GW 33 1 2.500000e-02 0.000000e+00 -4.323800e-01 2.500000e-02 -2.540000e-02 -4.323800e-01 2.413000e-03
' Middle Support
' bolt A 25mm 1"
GW 34 1 -2.500000e-02 0.000000e+00 3.327030e-01 -2.500000e-02 -2.540000e-02 3.327030e-01 2.413000e-03
' bolt B 25mm 1"
GW 35 1 2.500000e-02 0.000000e+00 3.327030e-01 2.500000e-02 -2.540000e-02 3.327030e-01 2.413000e-03
' bolt A 25mm 1"
GW 36 1 -2.500000e-02 0.000000e+00 -3.327030e-01 -2.500000e-02 -2.540000e-02 -3.327030e-01 2.413000e-03
' bolt B 25mm 1"
GW 37 1 2.500000e-02 0.000000e+00 -3.327030e-01 2.500000e-02 -2.540000e-02 -3.327030e-01 2.413000e-03
' Feed Support
' bolt A 25mm 1"
GW 38 1 -2.500000e-02 0.000000e+00 0.000000e+00 -2.500000e-02 -2.540000e-02 0.000000e+00 2.413000e-03
' bolt B 25mm 1"
GW 39 1 2.500000e-02 0.000000e+00 0.000000e+00 2.500000e-02 -2.540000e-02 0.000000e+00 2.413000e-03
' Feed width 50mm 1+15/16"
GW 20 1 2.500000e-02 0.000000e+00 0.000000e+00 -2.500000e-02 0.000000e+00 0.000000e+00 1.650000e-03
GE 0 0 0 0 0 0 0 0 0
EX 0 20 1 0 0 0 0 0 0
ZO 300 0 0 0 0 0 0 0 0 0
' VHF Scan
FR 0 7 0 0 1.770000e+02 6.000000e+00 2.130000e+02 0 0 0
' UHF Scan
FR 0 23 0 0 4.730000e+02 6.000000e+00 6.050000e+02 0 0 0
RP 0 38 73 0 0 0 5 5 0 0
' End
EN 0 0 0 0 0 0 0 0 0