CM4221a.ez EZNEC file 4-Bay Antenna with Reflector removed. Illustrates one of the BETTER 4-Bay Antenna designs. Dimensions from Ken Nist's cm4221a.ez NEC file are SAME as HALF of cm4228a.ez (Demi-CM4228). Long feed (simulating twin-lead?) was changed to simple Balun Source (BS) or simple Wire Source (WS) to fix VHF AvgGainTest.
BowLength = 7.8-in, Bowtie Spacing = 8-in, Tine Separation = 5.5-in. Feedline Separation = 1.25-in, with 0.8-in at Crossover. In fol. 4nec2 simulation, per Ken Nist's EZNEC file, a simple 1.25-in SOURCE wire (SW) interconnects the feedlines. Runs with a Simulated Balun SOURCE (BS) feed yield very similar results.
UHF Raw Gain increases with frequency from 6.5 dBi to 12 dBi. SWR under 5.0 at low freqs, decreasing at highest freqs to 1.5.
VHF Raw Gain is constant 4.1 dBi. EXCESSIVE SWR decreases with frequency. Ch13 may be usable but ineffective on Ch7-12.
Date(s): 26 Feb 2009. Album by holl_ands. 1 - 16 of 16 Total. 9540 Visits.
enlarge 0KB, 768x1024 1 CM4221 Hung from the Rafters
Note Reflector Screen flare is to the Rear for slightly wider Beamwidth.
enlarge 0KB, 527x1024 2 CM4221a with No Reflector - 3D View
enlarge 0KB, 584x1024 3 CM4221a with No Reflector - Front View
Each small box = 0.5 inch
enlarge 0KB, 296x1024 4 CM4221a with No Reflector - Side View
Note wires maintain 0.8-in separation at crossovers
enlarge 0KB, 445x1024 5 CM4221a with No Reflector - Top View
Each small box = 0.5 inch
enlarge 28KB, 791x1024 6 4nec2 file for CM4221a 4-Bay with No Reflector
Use Wordpad to "Save As" *.txt file, then change *.txt to *.nec
enlarge 0KB, 1024x819 7 CM4221a with No Reflector - UHF Raw Gain
Increases with frequency from 6.5 to 12 dBi.
enlarge 0KB, 1024x819 8 CM4221a with No Reflector - UHF SWR
Decreases from 5.0 at low freqs to 1.5 at highest. 300-ohm is best overall load impedance.
enlarge 0KB, 1024x819 9 CM4221a with No Reflector - UHF Impedance
enlarge 0KB, 1024x819 10 CM4221a with No Reflector - UHF SWR
150-ohm is slightly better at Hi-Freqs, but worse for Low and Mid-Freqs.
enlarge 0KB, 1024x819 11 CM4221a with No Reflector - UHF SWR
600-ohm better Mid-band, but worse for Low and Hi Freqs.
enlarge 0KB, 1024x819 12 Average Gain Test for UHF Frequency
Keep clicking on image to see higher resolutions. Click on "X" as usual to exit Windows.
enlarge 0KB, 1024x819 13 CM4221a with No Reflector - Hi-VHF Raw Gain
Constant 4.1 dBi across all channels.
enlarge 0KB, 1024x819 14 CM4221a with No Reflector - Hi-VHF SWR
EXCESSIVE on low channels, dropping to moderate on Ch13.
SWR Reduces Net Gain.
enlarge 0KB, 1024x819 15 CM4221a with No Reflector - Hi-VHF Impedance
enlarge 0KB, 1024x819 16 Average Gain Test for Hi-VHF Frequency
