New CM4228HD (As Shipped) analyzed using 4nec2. I obtained measurements directly from a recently delivered antenna. Note that Ken Nist (of HDTVPrimer) determined that the Printed Circuit Board (PCB) Balun ATTENUATED Hi-VHF Gain by 3 dB, which is NOT included in below results. This can be avoided if the PCB Balun is replaced by a conventional 4:1 Balun Transformer.
Choice of AutoSegmentation value (typ. 7 or 11) was very critical to finding a "workable" solution and was different for UHF & Hi-VHF.
BowLength = 8.0-in, Bowtie Spacing = 8.0-in, Tine Separation = 4.75-in. Approx. AWG6 wire size (0.157" O.D.). Feedline Separation = 1.3-in, with 0.5-in Hop at Crossover. AWG9 wire size (0.118" O.D.). Center of Crossovers 1.5-in from Center of Outer Bowties. Left to Right Bay Separation = 20-in. 16 each AWG4 (0.2-in O.D.), 40-in long Reflector Rods, at 4-in separation (32-in Total Height). Separation from Bowties = 4.4-in.
UHF Gain is about 14 dBi on most channels, dropping to 10.5 dBi on Ch14. Excellent SWR under 2.0. Hi-VHF Gain is very uneven with Excessive SWR on most channels, but remains pointed in the Forward direction.
Charts are included comparing CM4228HD (As Shipped) to older CM4228, as well as comparisons to mclapp's M4 Super-Sized 4-Bay and CM4228/CM4228HD with & w/o RF Combiner Mod.
New CM4228HD (As Shipped) was much better than old CM4228 on the (problematic) lowest channels, but had 1-2 dB lower Gain above Ch30. New CM4228HD was actually somewhat worst than mclapp M4 Super-4-Bay, esp on lowest channels.
Sweeping the TIPS of the Bowties directly forward by (optimum) 1-inch provided only up to 1 dB of Gain improvement at the expense of up to 2 dB of reduction in F_B and F_R Ratios. So might not be worth it.
Modifying the vertical Tine Separation between the TIPS of the Bowties by (optimum) of 2-inch separation resulted in only up to 1 dB Gain increase at mid and high channels and up to 3 dB on lowest channels. On-Air Tests are needed to verify.
Combiner Mod for New CM4228HD compared to "As Shipped" to illustrate how much is lost in the horizontal interconnect. If a low loss RF Combiner Module is used (not an easy task), more than 2 dB of improvement MIGHT be possible.... Bear in mind that an RF Combiner Module will have AT LEAST 0.5 dB Loss (and likely more on higher freqs) not shown in the charts, see actual RF Splitter/Combiner measurements at www.antennahacks.com (back-to-back tests, so divide by 2).
NOTE: The Autosegment feature of 4nec2 was used to determine how many wire segments to use when modeling each wire element. The choice of Autosegment=11 was very critical in getting the CM-4228HD Gain and SWR calculations to work AT ALL. And small changes to Autosegment resulted in large changes in Hi-VHF Gain & SWR....so Hi-VHF results might not be all that accurate.
EDIT (29Mar2013): Added (Slides 16-21) ANOMALOUS plots versus Bowtie Tine Separation and Bowtie Forward Sweep, which can frustrate finding an "Optimum" set of dimensions. I believe that this is a 4nec2 Modeling anomaly, rather than inherent in CM4228HD design. There's NO WAY Whisker movements of a couple thousandths of an inch result in BIG Gain changes.
Also added (Slide 39) ANOMALOUS Small Perturbation Test Results showing Raw Gain varies as much as +/- 1.0 dB when Bowtie Tine Separation and Bowtie Forward Sweep are Randomly Perturbed by up to +/- 0.25-in, using EXCEL's 0.0001*RANDBETWEEN(-2500,2500) function to generate variables. Indicates that Raw Gain at 470 MHz may actually be closer to 13.0 dBi than 10.5 dBi found in "unperturbed" 4nec2 Model.
Date(s): 28 Aug 2010. Album by holl_ands. 1 - 45 of 45 Total. 17084 Visits.
enlarge 226KB, 1024x696 1 Comparing CM4228HD vs older CM4228 vs mclapp M4 UHF Raw Gain & Net Gain
enlarge 279KB, 1024x696 2 Comparing CM4228HD vs older CM4228 vs mclapp M4 With and without RF Combiner Mod UHF Raw Gain & Net Gain
enlarge 272KB, 1024x696 3 Comparing CM4228HD vs older CM4228 vs mclapp M4 With and without RF Combiner Mod UHF Front/Rear and Front/Back Ratios
enlarge 233KB, 1024x696 4 CM4228HD: If Sweep Bows FORWARD or BACK UHF Raw Gain & Net Gain
Sweeping FORWARD 1-in improves lowest channels and highest channels by about 1 dB.
enlarge 266KB, 1024x696 5 CM4228HD: If Sweep Bows FORWARD or BACK UHF F/R & F/B Ratios
Sweeping FORWARD 1-in results in small degradation to F/R & F/B Ratios.
enlarge 414KB, 1024x768 6 CM4228HD Hanging From Pergola NOTE re Horizontal Interconnect Harness: Rivets drilled out and replaced by 1-in #8 Screws in preparation for connecting RF Combiner Mod.
enlarge 243KB, 1024x696 7 CM4228HD: If Modify Whisker Tine Separation UHF Raw Gain & Net Gain
Closing Tine Separation to 2.0-in improves Gain on mid and high channels by up to 1 dB and up to 3 dB on the lowest channels.
Closing Tine Separation to 2.0-in reduces F_B by 1-3 dB on lowest channels, and F_R by up to 1 dB.
enlarge 320KB, 664x1024 9 CM4228HD Hanging From Pergola With RF Combiner Mod (note two Baluns). Rivets drilled out and replaced by 1-in #8 Screws.
enlarge 236KB, 917x1024 10 New CM4228HD - As Shipped 3D View
enlarge 257KB, 1024x729 11 New CM4228HD - As Shipped Front View [1 small box = 1-inch]
enlarge 70KB, 290x1024 12 New CM4228HD - As Shipped Top View [1 small box = 1-inch]
enlarge 158KB, 1024x648 13 New CM4228HD - As Shipped UHF Raw Gain, F/B and F/R Ratios Drops off several dB on lowest channels.
enlarge 149KB, 1024x648 14 New CM4228HD - As Shipped UHF SWR (300-ohm) is Excellent.
enlarge 145KB, 1024x648 15 New CM4228HD - As Shipped UHF Impedance
enlarge 202KB, 1152x678 16 New CM4228HD - As Shipped Raw Gain vs Bowtie Tine Separation ANOMALOUS RESULTS at 470 MHz
enlarge 211KB, 1152x678 17 New CM4228HD - As Shipped SWR (300-ohms) vs Bowtie Tine Separation ANOMALOUS RESULTS at 470 MHz
enlarge 255KB, 1152x678 18 New CM4228HD - As Shipped Impedance vs Bowtie Tine Separation ANOMALOUS RESULTS at 470 MHz
enlarge 192KB, 1152x678 19 New CM4228HD - As Shipped Raw Gain vs Bowtie Forward Sweep ANOMALOUS RESULTS at 470 MHz
enlarge 208KB, 1152x678 20 New CM4228HD - As Shipped SWR (300-ohms) vs Bowtie Forward Sweep ANOMALOUS BLIPS
enlarge 245KB, 1152x678 21 New CM4228HD - As Shipped Impedance vs Bowtie Forward Sweep ANOMALOUS RESULTS at 470 MHz
enlarge 307KB, 1024x1024 22 New CM4228HD - As Shipped UHF Azimuthal Pattern at 470 MHz
enlarge 306KB, 1024x1024 23 New CM4228HD - As Shipped UHF Azimuthal Pattern at 590 MHz
enlarge 307KB, 1024x1024 24 New CM4228HD - As Shipped UHF Azimuthal Pattern at 698 MHz
enlarge 309KB, 1024x1024 25 New CM4228HD - As Shipped UHF Azimuthal Pattern at 758 MHz
enlarge 310KB, 1024x1024 26 New CM4228HD - As Shipped UHF Azimuthal Pattern at 806 MHz
enlarge 82KB, 369x1024 27 New CM4228HD - As Shipped Side View [1 small box = 1-inch]
enlarge 137KB, 1024x648 28 New CM4228HD - As Shipped Hi-VHF Raw Gain is very uneven. Peaky 10 dBi Gain on part of Ch10, but drops below 0 dBi on Ch9.
enlarge 163KB, 1024x648 29 New CM4228HD - As Shipped Hi-VHF SWR (300-ohm) Excessive except on problematic Ch9/10.
enlarge 143KB, 1024x648 30 New CM4228HD - As Shipped Hi-VHF Impedance
enlarge 310KB, 1024x1024 31 New CM4228HD - As Shipped Hi-VHF Azimuthal Pattern at 174 MHz
enlarge 307KB, 1024x1024 32 New CM4228HD - As Shipped Hi-VHF Azimuthal Pattern at 183 MHz
enlarge 304KB, 1024x1024 33 New CM4228HD - As Shipped Hi-VHF Azimuthal Pattern at 187.5 MHz
enlarge 316KB, 1024x1024 34 New CM4228HD - As Shipped Hi-VHF Azimuthal Pattern at 196.5 MHz
enlarge 306KB, 1024x1024 35 New CM4228HD - As Shipped Hi-VHF Azimuthal Pattern at 207 MHz
enlarge 305KB, 1024x1024 36 New CM4228HD - As Shipped Hi-VHF Azimuthal Pattern at 216 MHz
enlarge 76KB, 548x1024 37 New CM4228HD - As Shipped 3D View Reflector Rods Removed for Clarity In HHH, 2-in Space between Top/Bottom Wires
enlarge 335KB, 1024x959 38 New CM4228HD - As Shipped Front View Reflector Rods Removed for Clarity [1 large square = 2.5 inches] In HHH, all Long wires = 4.1875-in and all Short wires = 1-in.
enlarge 87KB, 279x1024 39 New CM4228HD - As Shipped Top View Reflector Rods Removed for Clarity [1 large square = 2.5 inches] HHH about 5/16-in behind Bowties
enlarge 46KB, 791x1024 40 New CM4228HD - As Shipped 4nec2 File - UHF Band ONLY See below for Hi-VHF version.
enlarge 46KB, 791x1024 41 New CM4228HD - As Shipped 4nec2 File - Hi-VHF Band ONLY See above for UHF version.
enlarge 50KB, 791x1024 42 New CM4228HD - As Shipped 4nec2 File - Example for Perturbation Test
enlarge 275KB, 1024x696 43 New CM4228HD - As Shipped Raw Gain Perturbation Test
enlarge 101KB, 1152x249 44 New CM4228HD - As Shipped Original Horizontal Interconnect Harness FRONT - Click to see Med-Rez and TWICE MORE for Hi-Rez
enlarge 116KB, 1152x281 45 New CM4228HD - As Shipped Original Horizontal Interconnect Harness BACK - Click to see Med-Rez and TWICE MORE for Hi-Rez
Hello. I note on the page at back-to-back tests, so divide by 2, and on this page I'm commenting on, you've cited my combiner comparison with the comment "back-to-back tests, so divide by 2". Would you please contact me? I'd like to understand what you mean by this. Thanks. - Tom | antennahacks.com, Mon, 8 Feb 2016 1:20PM
