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 holl_ands | Home > Multi-Bay Bowtie Antennas > UHF 4-Bay Bowties with Reflector > 
UHF CM4221HD (Hacked) - 16 ReflRods
UHF (New) CM4221HD 4-Bay with 16 Reflector Rods (23.6-in Wide, Sep=4.25-in) modeled using 4nec2.

UHF Raw Gain=11.2-14.8 dBi. UHF SWR(300) under 2.1.
UHF F/B Ratio=19-33 dB and UHF F/R Ratio=15-18 dB.

NOTE: CM4221HD's PCB Balun ATTENUATES VHF, however if REPLACE Balun then:
Hi-VHF Raw Gain=3-6.6 dBi (FORWARD), but HIGHER Hi-VHF Raw Gain=7.7-5.0 dBi (TOWARDS REAR!).
Hi-VHF SWR(300)=EXCESSIVE, esp. on lower Hi-VHF channels.

CM4221HD measurements per fol. smpowell55 posts:
http://www.digitalhome.ca/forum/showthread.php?p=863127
http://www.digitalhome.ca/forum/showthread.php?p=863559

BowLength = 7.9-in, Inner-Inner Bowtie Spacing = 9.84-in, Outer-Inner Bowtie Spacing = 8.46-in,
Tine Separation = 3.94-in.  Feedline Separation = 1.18-in, with 0.8-in at Crossover (2" from Outer Bowtie).
16 Rod Reflectors: 23.6" Long with 1.93" Spacings for Total Height = 30-in.  Separation from Bowties = 4.25-in.

It is presumed that anyone interested enough to view this webpage will
implement the "Hacked Balun" modifications per photo in fol. rabbit73 post
(flip over the Feedlines going into the Balun plus an additional offset):
http://www.digitalhome.ca/forum/showthread.php?p=1167870

Although NEW, the CM4221HD is still optimized for the OLD UHF Band (up thru Ch69), wasting the Max Gain peak
on channels that are no longer available for DTV.  UHF Raw Gain is about the same as older CM4221 with
improved UHF SWR on the lower channels....and Hi-VHF Raw Gain & SWR, such as it is, has been degraded....

Super-Sized-4-Bays have better Gain on New UHF Band (up thru Ch51) and don't have a Hi-VHF Gain Reversal problem.

EDIT (30Mar2013): Added (Slides 7-12) MOSTLY NORMAL plots versus Bowtie Tine Separation and
Bowtie Forward Sweep, although at more than 1-1/2 inch increase in Tine Separation, a significant
Gain & SWR Glitch was found, which could frustrate finding an "Optimum" set of dimensions.
This may or may not be a 4nec2 Modeling anomaly, and might not be inherent in CM4221HD design.

Note that in 8-Bay Bowtie Antennas significant Gain & SWR glitches were found with very small
(under 0.5-in) changes in Tine Separation and Bowtie Forward Sweep from "As Built" dimensions.

EDIT (26Oct2013): Investigated comment below.  Segmentation in Feedline etc is as it should be.
However, when investigating other Autoseg numbers other than 11, I found that Autoseg(15)
and Autoseg(21) found "sharp angle warnings" and an AGT error resulting in 1 db lower Gain.
Since the Autoseg(11) did not find any "sharp angle warnings" and looks good, I'm sticking with it.

EDIT (26Oct2013): Added Rmax Parameter Sweep Charts (Reflector Rod Length = 2*Rmax) at 3 freqs.
Rmax can only be increased from 11.8 to 12.8-in before there is Gain LOSS on 698 MHz.
This mod would only result in a very minor (0.05 to 0.3 dB) improvement in overall Gain.

EDIT (3Apr2017): Added Elevation Angle Pattern Charts, showing NULLS at about 30-deg.
Date(s): 5 Oct 2011. Album by holl_ands. 1 - 36 of 36 Total. 7550 Visits.
Start SlideshowTo order prints and photo-products: 1. Select photos. 2. Click Order. 3. Select products.Select images and click to download to your computer 
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New CM4221HD 4-Bay w 16 Reflector Rods
3D View


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New CM4221HD 4-Bay w 16 Reflector Rods
Front View
[1 big box = 2.5-inches]


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New CM4221HD 4-Bay w 16 Reflector Rods
Side View
[1 big box = 2.5-inches]


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New CM4221HD 4-Bay w 16 Reflector Rods
UHF Raw Gain, F/B & F/R Ratios


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New CM4221HD 4-Bay w 16 Reflector Rods
UHFSWR (300-ohms) under 2.1


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New CM4221HD 4-Bay w 16 Reflector Rods
UHF Impedance


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New CM4221HD w 16 Reflector Rods
Raw Gain vs Bowtie Tine Separation, 470 MHz
NORMAL, but ANOMALIES 1.5-in away


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New CM4221HD w 16 Reflector Rods
SWR (300-ohms) vs Bowtie Tine Separation
NORMAL, but ANOMALIES 1-1/2 inches away


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New CM4221HD w 16 Reflector Rods
Impedance vs Bowtie Tine Separation
NORMAL, but ANOMALIES 1-1/2 inches away


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New CM4221HD w 16 Reflector Rods
Raw Gain vs Bowtie Forward Sweep
NORMAL RESULTS at 470 MHz


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New CM4221HD w 16 Reflector Rods
SWR (300-ohms) vs Bowtie Forward Sweep
NORMAL RESULTS at 470 MHz


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New CM4221HD w 16 Reflector Rods
Impedance vs Bowtie Forward Sweep
NORMAL RESULTS at 470 MHz


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New CM4221HD 4-Bay w 16 Reflector Rods
Azimuthal Pattern at 470 MHz


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New CM4221HD 4-Bay w 16 Reflector Rods
Azimuthal Pattern at 590 MHz


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New CM4221HD 4-Bay w 16 Reflector Rods
Azimuthal Pattern at 698 MHz


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New CM4221HD 4-Bay w 16 Reflector Rods
Azimuthal Pattern at 758 MHz


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New CM4221HD 4-Bay w 16 Reflector Rods
Azimuthal Pattern at 806 MHz


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New CM4221HD 4-Bay w 16 Reflector Rods
Top View
[1 big box = 2.5-inches]


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New CM4221HD 4-Bay w 16 Reflector Rods
Hi-VHF Raw Gain FORWARD


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New CM4221HD 4-Bay w 16 Reflector Rods
Hi-VHF Raw Gain, F/B & F/R Ratios HIGHER to REAR


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New CM4221HD 4-Bay w 16 Reflector Rods
Hi-VHF SWR (300-ohms) is EXCESSIVE


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New CM4221HD 4-Bay w 16 Reflector Rods
Azimuthal Pattern at 174 MHz


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New CM4221HD 4-Bay w 16 Reflector Rods
Azimuthal Pattern at 186 MHz


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New CM4221HD 4-Bay w 16 Reflector Rods
Azimuthal Pattern at 198 MHz


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New CM4221HD 4-Bay w 16 Reflector Rods
Azimuthal Pattern at 207 MHz


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New CM4221HD 4-Bay w 16 Reflector Rods
Azimuthal Pattern at 216 MHz


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DOC27
New CM4221HD 4-Bay w 16 Reflector Rods
4nec2 File


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New CM4221HD 4-Bay w 16 Reflector Rods
Elevation Pattern at 470 MHz


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New CM4221HD 4-Bay w 16 Reflector Rods
Elevation Pattern at 530 MHz


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New CM4221HD 4-Bay w 16 Reflector Rods
Elevation Pattern at 590 MHz


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New CM4221HD 4-Bay w 16 Reflector Rods
Elevation Pattern at 650 MHz


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New CM4221HD 4-Bay w 16 Reflector Rods
Elevation Pattern at 698 MHz


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New CM4221HD 4-Bay w 16 Reflector Rods
Elevation Pattern at 806 MHz


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New CM4221HD 4-Bay w 16 Reflector Rods
Rmax Parameter Sweep at 470 MHz
[Reflector Rod Length = 2*Rmax]

Gain increases 0.4 dB if Rmax 11.8 to 15.8-in.


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New CM4221HD 4-Bay w 16 Reflector Rods
Rmax Parameter Sweep at 584 MHz
[Reflector Rod Length = 2*Rmax]

Gain increases 0.5 dB if Rmax from 11.8 to 14.8-in.


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New CM4221HD 4-Bay w 16 Reflector Rods
Rmax Parameter Sweep at 698 MHz
[Reflector Rod Length = 2*Rmax]

Gain increases 0.05 dB if Rmax from 11.8 to 12.8-in,
however for larger Rmax, Gain is REDUCED.


 Select All.  
  Sign the Guestbook. Displaying 3 of 3 entries.
Segmentation is CORRECT.  I used 4nec2's Autosegmentation feature.  As shown in the posted 4nec2 File, the longest sections in the Feedline are 7 segments, medium length sections 3 segments and the short segments in the Crossover "Hop" are just 1 segment.
 - 
holl_ands, Fri, 2 Aug 2019 12:15PM
Impressive Work !
 - 
Howard | Http://www.fcc1.biz, Thu, 29 Nov 2018 8:15AM
The file provided has single segments for the feedline, which results in excessively good performance; when changed to normal, the nice performance is gone...

However, I corrected that and changed a few things, now I have something better than the data here shows.
 - 
ohai, Sun, 11 Aug 2013 11:53AM