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 holl_ands | Home > Stacked Antennas > Horizontally Stacked UHF Antennas > 
Horiz-Stck 2xCM4221HD Hacked - NULL BEAM
UHF Horizontally Stacked 2xCM4221HD (Hacked), connected Out-Of-Phase for a NULL on-axis,
with 2 or more Beams on either side, described on HDTVPrimer as the "Two-Antenna Trick":
http://www.hdtvprimer.com/antennas/ganging.html

Since the original CM4221's are no longer available, the replacement CM4221HD was analyzed.

As shown in the charts for five different Horizontal Stacking Distances, a fairly deep Null can
be formed directly on-axis, with Narrow Beams formed on either side of the Null.  For some
combinations of Frequency and Stacking Distance, an additional pair of usable Beams may or
may not be formed at angles even further away.
BTW: Horiz. Stacking Distance is between the Centers of each 4-Bay.

Note that for this CM4221HD example (which has a fairly wide Beamwidth), the third pair of
Beams has very little usable Gain.  Different Antennas will likely exhibit different performance.

The Chart at the bottom plots the Angle between the forward Null and the Adjacent Beams,
as well as the Secondary Beams (if usable Gain) versus the Horizontal Stacking Distance.

Using CM4221HD's, (without modifications), the Reflector Rods limit how close the 4-Bays
can be mounted.  With modifications, the Null-to-Beam Angle could be increased a bit more.

To receive a weak station separated by a very small Angle from a strong local station,
the two Antennas need to have a fairly large Stacking Distance...far more than would be
feasible mounted on a typical Rotator, which is limited in it's ability to tolerate strong
twisting in the wind.  If using fixed locations for the two Antennas, their location(s)
would need to be carefully adjusted while monitoring how well the strong local station
is nulled out.  In similar Antenna sidelobe nulling adjustments, I had to add a Variable
RF Attenuator to reduce the tuner signals levels closer to threshold to "see" the null.

Per the Azimuthal Pattern Charts, strong signals should be attenuated at least 10-15 dB
relative to the weak desired signal.  Actual On-Air tests would need to be conducted
to verify this prediction and see if even deeper Nulls are possible given "real world"
inaccuracies in pointing the Array and matching the Antennas [doublecheck dimensions].
Date(s): 20 Dec 2013. Album by holl_ands. 1 - 76 of 76 Total. 3513 Visits.
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H-Stk CM4221HD NULL BEAM D = 24-in
3D View


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H-Stk CM4221HD NULL BEAM D = 24-in
Front View
[1 large square = 12.5 inches]


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H-Stk CM4221HD NULL BEAM D = 24-in
Top View
[1 large square = 12.5 inches]


Enlarge photo 4
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4
H-Stk CM4221HD NULL BEAM D = 24-in
UHF Raw Gain = 11.4 to 15.0 dBi
for Azimuth = 71 & 109-deg


Enlarge photo 5
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5
H-Stk CM4221HD NULL BEAM D = 24-in
UHF SWR (300-ohms) Under 4.3 is a Bit High


Enlarge photo 6
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6
H-Stk CM4221HD NULL BEAM D = 24-in
UHF Impedance


Enlarge photo 7
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7
H-Stk CM4221HD NULL BEAM D = 24-in
Azimuthal Pattern at 470 MHz


Enlarge photo 8
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8
H-Stk CM4221HD NULL BEAM D = 24-in
Azimuthal Pattern at 530 MHz


Enlarge photo 9
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9
H-Stk CM4221HD NULL BEAM D = 24-in
Azimuthal Pattern at 590 MHz


Enlarge photo 10
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10
H-Stk CM4221HD NULL BEAM D = 24-in
Azimuthal Pattern at 650 MHz


Enlarge photo 11
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11
H-Stk CM4221HD NULL BEAM D = 24-in
Azimuthal Pattern at 698 MHz


Enlarge photo 12
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H-Stk CM4221HD NULL BEAM D = 24-in
Azimuthal Pattern at 758 MHz


Enlarge photo 13
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13
H-Stk CM4221HD NULL BEAM D = 24-in
Azimuthal Pattern at 806 MHz


Enlarge Microsoft Word Document 14
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DOC14
H-Stk CM4221HD NULL BEAM D = 24-in
4nec2 File


Enlarge photo 15
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15
H-Stk CM4221HD NULL BEAM D = 24-in
Side View
[1 large square = 2.5 inches]


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16
H-Stk CM4221HD NULL BEAM D = 40-in
3D View


Enlarge photo 17
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17
H-Stk CM4221HD NULL BEAM D = 40-in
Front View
[1 large square = 12.5 inches]


Enlarge photo 18
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H-Stk CM4221HD NULL BEAM D = 40-in
Top View
[1 large square = 12.5 inches]


Enlarge photo 19
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19
H-Stk CM4221HD NULL BEAM D = 40-in
UHF Raw Gain = 12.8 to 16.5 dBi
for Azimuth = 77 & 103-deg


Enlarge photo 20
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20
H-Stk CM4221HD NULL BEAM D = 40-in
UHF SWR (300-ohms) Under 4.2 is a Bit High


Enlarge photo 21
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21
H-Stk CM4221HD NULL BEAM D = 40-in
UHF Impedance


Enlarge photo 22
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22
H-Stk CM4221HD NULL BEAM D = 40-in
Azimuthal Pattern at 470 MHz


Enlarge photo 23
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23
H-Stk CM4221HD NULL BEAM D = 40-in
Azimuthal Pattern at 530 MHz


Enlarge photo 24
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24
H-Stk CM4221HD NULL BEAM D = 40-in
Azimuthal Pattern at 590 MHz


Enlarge photo 25
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25
H-Stk CM4221HD NULL BEAM D = 40-in
Azimuthal Pattern at 650 MHz


Enlarge photo 26
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26
H-Stk CM4221HD NULL BEAM D = 40-in
Azimuthal Pattern at 698 MHz


Enlarge photo 27
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27
H-Stk CM4221HD NULL BEAM D = 40-in
Azimuthal Pattern at 758 MHz


Enlarge photo 28
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28
H-Stk CM4221HD NULL BEAM D = 40-in
Azimuthal Pattern at 806 MHz


Enlarge Microsoft Word Document 29
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DOC29
H-Stk CM4221HD NULL BEAM D = 40-in
4nec2 File


Enlarge photo 30
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30
H-Stk CM4221HD NULL BEAM D = 40-in
Side View
[1 large square = 2.5 inches]


Enlarge photo 31
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31
H-Stk CM4221HD NULL BEAM D = 60-in
3D View


Enlarge photo 32
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32
H-Stk CM4221HD NULL BEAM D = 60-in
Front View
[1 large square = 12.5 inches]


Enlarge photo 33
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33
H-Stk CM4221HD NULL BEAM D = 60-in
Top View
[1 large square = 12.5 inches]


Enlarge photo 34
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34
H-Stk CM4221HD NULL BEAM D = 60-in
UHF Raw Gain = 13.3 to 17.1 dBi
for Azimuth = 81 & 99-deg


Enlarge photo 35
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35
H-Stk CM4221HD NULL BEAM D = 60-in
UHF SWR (300-ohms) Under 4.2


Enlarge photo 36
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36
H-Stk CM4221HD NULL BEAM D = 60-in
UHF Impedance


Enlarge photo 37
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37
H-Stk CM4221HD NULL BEAM D = 60-in
Azimuthal Pattern at 470 MHz


Enlarge photo 38
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38
H-Stk CM4221HD NULL BEAM D = 60-in
Azimuthal Pattern at 530 MHz


Enlarge photo 39
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39
H-Stk CM4221HD NULL BEAM D = 60-in
Azimuthal Pattern at 590 MHz


Enlarge photo 40
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40
H-Stk CM4221HD NULL BEAM D = 60-in
Azimuthal Pattern at 650 MHz


Enlarge photo 41
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41
H-Stk CM4221HD NULL BEAM D = 60-in
Azimuthal Pattern at 698 MHz


Enlarge photo 42
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42
H-Stk CM4221HD NULL BEAM D = 60-in
Azimuthal Pattern at 758 MHz


Enlarge photo 43
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43
H-Stk CM4221HD NULL BEAM D = 60-in
Azimuthal Pattern at 806 MHz


Enlarge Microsoft Word Document 44
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DOC44
H-Stk CM4221HD NULL BEAM D = 60-in
4nec2 File


Enlarge photo 45
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45
H-Stk CM4221HD NULL BEAM D = 60-in
Side View
[1 large square = 2.5 inches]


Enlarge photo 46
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46
H-Stk CM4221HD NULL BEAM D = 60-in
3D View


Enlarge photo 47
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47
H-Stk CM4221HD NULL BEAM D = 80-in
Front View
[1 large square = 12.5 inches]


Enlarge photo 48
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48
H-Stk CM4221HD NULL BEAM D = 80-in
Top View
[1 large square = 12.5 inches]


Enlarge photo 49
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49
H-Stk CM4221HD NULL BEAM D = 80-in
UHF Raw Gain = 13.6 to 17.1 dBi
for Azimuth = 83 & 97-deg


Enlarge photo 50
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50
H-Stk CM4221HD NULL BEAM D = 80-in
UHF SWR (300-ohms) Under 4.2


Enlarge photo 51
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51
H-Stk CM4221HD NULL BEAM D = 80-in
UHF Impedance


Enlarge photo 52
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52
H-Stk CM4221HD NULL BEAM D = 80-in
Azimuthal Pattern at 470 MHz


Enlarge photo 53
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53
H-Stk CM4221HD NULL BEAM D = 80-in
Azimuthal Pattern at 530 MHz


Enlarge photo 54
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54
H-Stk CM4221HD NULL BEAM D = 80-in
Azimuthal Pattern at 590 MHz


Enlarge photo 55
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55
H-Stk CM4221HD NULL BEAM D = 80-in
Azimuthal Pattern at 650 MHz


Enlarge photo 56
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56
H-Stk CM4221HD NULL BEAM D = 80-in
Azimuthal Pattern at 698 MHz


Enlarge photo 57
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57
H-Stk CM4221HD NULL BEAM D = 80-in
Azimuthal Pattern at 758 MHz


Enlarge photo 58
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58
H-Stk CM4221HD NULL BEAM D = 80-in
Azimuthal Pattern at 806 MHz


Enlarge Microsoft Word Document 59
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DOC59
H-Stk CM4221HD NULL BEAM D = 80-in
4nec2 File


Enlarge photo 60
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60
H-Stk CM4221HD NULL BEAM D = 80-in
Side View
[1 large square = 2.5 inches]


Enlarge photo 61
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61
H-Stk CM4221HD NULL BEAM D = 120-in
3D View


Enlarge photo 62
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62
H-Stk CM4221HD NULL BEAM D = 120-in
Front View
[1 large square = 12.5 inches]


Enlarge photo 63
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63
H-Stk CM4221HD NULL BEAM D = 120-in
Top View
[1 large square = 12.5 inches]


Enlarge photo 64
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64
H-Stk CM4221HD NULL BEAM D = 120-in
UHF Raw Gain = 14.1 to 15.4 to 14.7 dBi
for Azimuth = 84 & 96-deg


Enlarge photo 65
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65
H-Stk CM4221HD NULL BEAM D = 120-in
UHF SWR (300-ohms) Under 4.1


Enlarge photo 66
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66
H-Stk CM4221HD NULL BEAM D = 120-in
UHF Impedance


Enlarge photo 67
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67
H-Stk CM4221HD NULL BEAM D = 120-in
Azimuthal Pattern at 470 MHz


Enlarge photo 68
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68
H-Stk CM4221HD NULL BEAM D = 120-in
Azimuthal Pattern at 530 MHz


Enlarge photo 69
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69
H-Stk CM4221HD NULL BEAM D = 120-in
Azimuthal Pattern at 590 MHz


Enlarge photo 70
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70
H-Stk CM4221HD NULL BEAM D = 120-in
Azimuthal Pattern at 650 MHz


Enlarge photo 71
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71
H-Stk CM4221HD NULL BEAM D = 120-in
Azimuthal Pattern at 698 MHz


Enlarge photo 72
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72
H-Stk CM4221HD NULL BEAM D = 120-in
Azimuthal Pattern at 758 MHz


Enlarge photo 73
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73
H-Stk CM4221HD NULL BEAM D = 120-in
Azimuthal Pattern at 806 MHz


Enlarge Microsoft Word Document 74
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DOC74
H-Stk CM4221HD NULL BEAM D = 120-in
4nec2 File


Enlarge photo 75
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75
H-Stk CM4221HD NULL BEAM D = 120-in
Side View
[1 large square = 2.5 inches]


Enlarge photo 76
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76
Horiz-Stack CM4221HD NULL BEAM
Angle Between Null and Beams (degrees)


 
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