VHF Stick Dipoles of various Length Elements (3/8-in Diameter & 1/4-in Rabbit-Ears in Horizontal configuration) analyzed using 4nec2. Overall-Lengths of the longer Stick Dipoles are typical for VHF/UHF Combo Antenna widths.
Note that when matched to the "natural" dipole impedance of 75-ohms, SWR is very narrowband. Better wideband performance is found when terminate into 300-ohms. [Raw Gain is unaffected.]
For Ch2 (57 MHz center freq), it's necessary to match a Total Length of 98.5 inches to 75-ohms, since 300-ohm load yields Excessive SWR. The resultant Antenna has just barely enough low SWR bandwidth for Ch2 and should be located at least several inches away from nearby objects, whether metal or not, to prevent detuning the Antenna. For Ch3, best Total Length would be 86.25-inches, with similar results, when matched into 75-ohms [direct connect Coax to Center of Dipole].
For the Ch2 & Ch3 narrowband antennas, wire as small as AWG12 provided acceptable SWR and same Gain as 3/8-in Aluminum. Twinlead with AWG24 not recommended for Ch2-4 due to poor SWR.
Many/most Rabbit-Ear Antennas can not be extended enough to provide acceptable (under 2.7) SWR on Ch2 & Ch3. "Best" Gain (only 2 dBi) & SWR (Excessive, under 5) for Hi-VHF Band is when Half-Lengths = 14.5-inches. Impedance Matching Networks in the Rabbit-Ears base can improve on this SWR...unfortunately manufacturers' don't want to disclose specs....so don't expect much of an improvement....
EDIT (16Jun2013): Added Total Length = 98.5 inches for Ch2, matched to 75-ohms, including an example 4nec2 File.
ERRATA (16Jun2013): Corrected "Half-Lengths" to "Overall-Length" in labels on all except first image, which correctly uses "Half-Lengths" when describing Rabbit-Ears.
Date(s): 24 Nov 2012. Album by holl_ands. 1 - 21 of 21 Total. 9408 Visits.
enlarge 229KB, 1024x696 1 VHF Stick Dipole - Different Sizes for Rabbit-Ear Half-Lengths (1/4-in Diameter) Raw Gain & SWR (300-ohms)
enlarge 33KB, 1024x884 2 Stick Dipole - 3D View Generic - Same for any Size
enlarge 146KB, 1152x584 4 VHF Stick Dipole Ch2-13 Raw Gain best on Ch7-13 Overall Length = 37.5-in Optimum for Ch7-13.
FYI: Max possible with RCA ANT110 Rabbit Ears when extended in Horizontal position.
enlarge 199KB, 1152x584 5 VHF Stick Dipole Ch2-13 SWR (75-ohms) Overall Length = 37.4-in Optimum for Ch7-13 Low SWR only for a narrow band near resonance.
enlarge 147KB, 1152x584 7 VHF Stick Dipole Ch2-13 Raw Gain Overall Length = 89-in
Gain Loss across Ch7-13
enlarge 197KB, 1152x584 8 VHF Stick Dipole Ch2-13 SWR (75-ohms) Overall Length = 89-in Low SWR only for a narrow band near Ch3 resonance AND near 194 MHz.
enlarge 138KB, 1152x584 10 VHF Stick Dipole Ch2-13 Raw Gain Overall Length = 95-in
Gain Loss across Ch7-13
enlarge 192KB, 1152x584 11 VHF Stick Dipole Ch2-13 SWR (75-ohms) Overall Length = 95-in Low SWR only for a narrow band near resonance AND near 180 MHz.
enlarge 141KB, 1152x584 13 VHF Stick Dipole Ch2-13 Raw Gain Overall Length = 110-in
Gain Loss across Ch7-13
enlarge 191KB, 1152x584 14 VHF Stick Dipole Ch2-13 SWR (75-ohms) Overall Length = 110-in Low SWR only for a narrow band near resonance AND near 156 MHz.
