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 holl_ands | Home > Multi-Bay Bowtie Antennas > UHF 8-Bay Bowtie with Reflector > 
New CM4228HD (As Shipped)
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. 13090 Visits.
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Comparing CM4228HD vs older CM4228 vs mclapp M4
UHF Raw Gain & Net Gain


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Comparing CM4228HD vs older CM4228 vs mclapp M4
With and without RF Combiner Mod
UHF Raw Gain & Net Gain


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Comparing CM4228HD vs older CM4228 vs mclapp M4
With and without RF Combiner Mod
UHF Front/Rear and Front/Back Ratios


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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.


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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.


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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.


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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.


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CM4228HD: If Modify Whisker Tine Separation
UHF F/R & F/B Ratios

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.


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CM4228HD Hanging From Pergola
With RF Combiner Mod (note two Baluns).
Rivets drilled out and replaced by 1-in #8 Screws.


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New CM4228HD - As Shipped
3D View


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New CM4228HD - As Shipped
Front View
[1 small box = 1-inch]


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New CM4228HD - As Shipped
Top View
[1 small box = 1-inch]


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New CM4228HD - As Shipped
UHF Raw Gain, F/B and F/R Ratios
Drops off several dB on lowest channels.


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New CM4228HD - As Shipped
UHF SWR (300-ohm) is Excellent.


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New CM4228HD - As Shipped
UHF Impedance


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New CM4228HD - As Shipped
Raw Gain vs Bowtie Tine Separation
ANOMALOUS RESULTS at 470 MHz


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New CM4228HD - As Shipped
SWR (300-ohms) vs Bowtie Tine Separation
ANOMALOUS RESULTS at 470 MHz


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New CM4228HD - As Shipped
Impedance vs Bowtie Tine Separation
ANOMALOUS RESULTS at 470 MHz


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New CM4228HD - As Shipped
Raw Gain vs Bowtie Forward Sweep
ANOMALOUS RESULTS at 470 MHz


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New CM4228HD - As Shipped
SWR (300-ohms) vs Bowtie Forward Sweep
ANOMALOUS BLIPS


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New CM4228HD - As Shipped
Impedance vs Bowtie Forward Sweep
ANOMALOUS RESULTS at 470 MHz


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New CM4228HD - As Shipped
UHF Azimuthal Pattern at 470 MHz


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New CM4228HD - As Shipped
UHF Azimuthal Pattern at 590 MHz


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New CM4228HD - As Shipped
UHF Azimuthal Pattern at 698 MHz


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New CM4228HD - As Shipped
UHF Azimuthal Pattern at 758 MHz


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New CM4228HD - As Shipped
UHF Azimuthal Pattern at 806 MHz


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New CM4228HD - As Shipped
Side View
[1 small box = 1-inch]


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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.


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New CM4228HD - As Shipped
Hi-VHF SWR (300-ohm)
Excessive except on problematic Ch9/10.


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New CM4228HD - As Shipped
Hi-VHF Impedance


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New CM4228HD - As Shipped
Hi-VHF Azimuthal Pattern at 174 MHz


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New CM4228HD - As Shipped
Hi-VHF Azimuthal Pattern at 183 MHz


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New CM4228HD - As Shipped
Hi-VHF Azimuthal Pattern at 187.5 MHz


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New CM4228HD - As Shipped
Hi-VHF Azimuthal Pattern at 196.5 MHz


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New CM4228HD - As Shipped
Hi-VHF Azimuthal Pattern at 207 MHz


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New CM4228HD - As Shipped
Hi-VHF Azimuthal Pattern at 216 MHz


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New CM4228HD - As Shipped
3D View
Reflector Rods Removed for Clarity
In HHH, 2-in Space between Top/Bottom Wires


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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.


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New CM4228HD - As Shipped
Top View
Reflector Rods Removed for Clarity
[1 large square = 2.5 inches]
HHH about 5/16-in behind Bowties


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DOC40
New CM4228HD - As Shipped
4nec2 File - UHF Band ONLY
See below for Hi-VHF version.


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DOC41
New CM4228HD - As Shipped
4nec2 File - Hi-VHF Band ONLY
See above for UHF version.


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DOC42
New CM4228HD - As Shipped
4nec2 File - Example for Perturbation Test


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New CM4228HD - As Shipped
Raw Gain Perturbation Test


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New CM4228HD - As Shipped
Original Horizontal Interconnect Harness
FRONT - Click to see Med-Rez and TWICE MORE for Hi-Rez


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New CM4228HD - As Shipped
Original Horizontal Interconnect Harness
BACK - Click to see Med-Rez and TWICE MORE for Hi-Rez


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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