UHF Vertically Stacked Channel Master (old) CM4221 analyzed using 4nec2.
Two versions are presented here, after using nikiml's Python Optimization Scripts to determine "best" Stacking Distance and Interconnection Parameters.
In both versions, Antennas are separated by a Fixed amount (Metal-Metal Between Screens = 4.05-inches) so that distance between Lower Bowtie on Upper Antenna and Upper Bowtie on Upper Antenna is 1.5 times the individual Bowtie-Bowtie Separation. This ANTI-MULTIPATH feature ensures that when Multipath conditions result in peaks and nulls varying with height, at least one Antenna will see mostly peaks when the other sees mostly nulls:
a) Two Equal Length 300-ohm Transmission Lines (aka "Twinlead") connect to a common Feedpoint for connection to a Balun (NO RF Combiner). This provides highest Raw Gain on higher channels, but is susceptible to increased loss when Twinlead gets wet.
UHF Raw Gain = 15.0 to 17.7 dBi, F/B & F/R Ratio Min = 11.9 dB & SWR (300-ohms) under 2.8. [With 440 or 450-ohm Ladderline SWR improves to under 2.4 & NO Change to Raw Gain, F/B or F/R Ratio.] Hi-VHF Raw Gain = 9.2 to 10.3 dBi REARWARD, with 4.9 to 7.7 dBi FORWARD and SWR (300-ohms) is EXCESSIVE except on Ch11. MORE HI-VHF GAIN TO REAR THAN FORWARD.
Note that Hi-VHF Pattern can be turned around to the FRONT by using a much wider Reflector, as was analyzed using M4 Super-4-Bay ("best" value T.B.D. for CM4221): http://imageevent.com/holl_ands/multibay/4bayrefl/m49590gridrefl55
More info re "Windowed" and "Open" Balanced Transmission Lines (latter is weather resistant): http://thewireman.com/antennap.html http://www.arrg.us/pages/Loss-Calc.htm [Note Wet Loss for WM-551, 552, 553 & 554]
####################################################### b) The second was Optimized using a Vertical Harness between the two CM4221's, where the distance between the Harness conductors and the Total Length was searched to find the "best" values.
UHF Raw Gain = 14.9 to 17.1 dBi, F/B & F/R Ratio Min = 11.2 dB and SWR (300-ohms) under 2.4. Hi-VHF Raw Gain = 8.6 to 10.5 dBi REARWARD, F/B & F/R Ratio Min = 5 to 3 dB and SWR (300-ohms) is EXCESSIVE except on Ch10. MORE HI-VHF GAIN TO REAR THAN FORWARD.
####################################################### Two other Optimizations were conducted where the Stacking Distance was one of the variables, but are not presented here since they had somewhat lower performance with Stacking Distance nearly the SAME as for versions above, so were essentially the same versions. One of these used Equal-Length Transmission Lines and the other a Vertical Harness similar to above.
Date(s): 25 Nov 2013. Album by holl_ands. 1 - 45 of 45 Total. 3515 Visits.
enlarge 138KB, 427x1024 1 V-Stack CM4221 4-Bay - Anti-MP Two TL's 3D View Metal-Metal Between Screens = 4.05-inches
enlarge 184KB, 359x1024 2 V-Stack CM4221 4-Bay - Anti-MP Two TL's Front View [1 large square = 5 inches]
enlarge 229KB, 954x1024 3 V-Stack CM4221 4-Bay - Anti-MP Two TL's Top View [1 large square = 2.5 inches]
enlarge 194KB, 1152x689 4 V-Stack CM4221 4-Bay - Anti-MP Two TL's UHF Raw Gain = 15.0 to 17.7 dBi UHF F/B & F/R Ratio Min = 11.9 dB
enlarge 199KB, 1152x689 5 V-Stack CM4221 4-Bay - Anti-MP Two TL's UHF SWR (300-ohms) Under 2.8 for Zfl = 300-ohms
enlarge 206KB, 1152x689 6 V-Stack CM4221 4-Bay - Anti-MP Two TL's UHF SWR (300-ohms) Under 2.3 for Zfl = 450-ohms [With NO Change to Raw Gain]
enlarge 205KB, 1152x689 7 V-Stack CM4221 4-Bay - Anti-MP Two TL's UHF SWR (300-ohms) Under 2.3 for Zfl = 600-ohms [With NO Change to Raw Gain]
enlarge 188KB, 1152x689 37 V-Stack CM4221 4-Bay - Anti-MP UHF Raw Gain = 8.6 to 10.5 dBi REARWARD UHF F/B & F/R Ratio Min = 5 to 3 dB MORE GAIN TO REAR THAN FORWARD
enlarge 176KB, 1152x689 38 V-Stack CM4221 4-Bay - Anti-MP UHF Raw Gain = 3.7 to 7.2 dBi FORWARD
enlarge 217KB, 1152x689 39 V-Stack CM4221 4-Bay - Anti-MP Harness UHF SWR (300-ohms) is EXCESSIVE except on Ch10
