Hi-VHF Offset-Crossed FD's

			• Public Gallery • Help

		• Join Now! • Log In • Feature Tour

Hi-VHF Offset-Crossed FD's - 2TL=3QWL

Hi-VHF Offset-Crossed Folded Dipoles (FD's) at Quarter-Wavelength Separation fed by two Transmission Lines,
each 3/4-Wavelength long. This results in an imperfect amplitude and phase difference in
signals arriving from each Folded Dipole, degrading RHCP (Right Hand Circular Polarization).
[NOTE: Included for illustration purposes only, TL=Half-Wavelength is correct length.]

Optimum TL is 600-ohm Impedance, although 450-ohm may also be used with minor degradation
to Gain and SWR. [In diagrams below, Feedlines are NOT TO SCALE.]

With Quarter-Inch Copper Tubing (QICT), 2-in FD "Width" (distance between FD Elements)
and Quarter-Wavelength Separation between the Crossed FD's, a large Gain and SWR GLITCH
was found in the middle of the Hi-VHF Band, the placement depending on the overall FD Length:
202 MHz if 28-in, etc.

If the length of the Cross-FDs are much longer or shorter than when used alone, the GLITCHES
can be moved out-of-band. The longer 34-in FD was better with good RHCP Gain, Fair to Good
LHCP suppression characteristics and good SWR.

Note that Right Hand Circular Polarization is strong both FORWARD and REVERSE, but Left Hand
suppression is stronger FORWARD. Reversing one interconnection reverses Polarization, so
VERY CAREFULLY check antenna connections and alignment.
Note Left Hand Circular Polarized (LHCP) signals are suppressed LESS THAN 10 dB relative to Right Hand (RHCP).

Date(s): 21 Jan 2012. Album by holl_ands. 1 - 22 of 22 Total. 1090 Visits.

enlarge 69KB, 853x1024 1 Hi-VHF Offset-Cross FD's - 2TL=3QWL Length = 34-in, Width=2-in 3D View	enlarge 302KB, 1024x976 2 Hi-VHF Offset-Cross FD's - 2TL=3QWL Length = 34-in, Width=2-in Front View [1 small box = 2.5-inches]	enlarge 162KB, 550x1024 3 Hi-VHF Offset-Cross FD's - 2TL=3QWL Length = 34-in, Width=2-in Top View [1 small box = 2.5-inches]
enlarge 162KB, 1024x686 4 Hi-VHF Offset-Cross FD's - 2TL=3QWL Hi-VHF Raw Gain ~ 2.85 to 3.05 dBi	enlarge 173KB, 1024x686 5 Hi-VHF Offset-Cross FD's - 2TL=3QWL Hi-VHF SWR (300-ohms) Under 2.3	enlarge 156KB, 1024x686 6 Hi-VHF Offset-Cross FD's - 2TL=3QWL Hi-VHF Impedance
enlarge 339KB, 1024x1024 7 Hi-VHF Offset-Cross FD's - 2TL=3QWL Azimuthal Patterns at 174 MHz	enlarge 337KB, 1024x1024 8 Hi-VHF Offset-Cross FD's - 2TL=3QWL Azimuthal Patterns at 186 MHz	enlarge 335KB, 1024x1024 9 Hi-VHF Offset-Cross FD's - 2TL=3QWL Azimuthal Patterns at 198 MHz
enlarge 339KB, 1024x1024 10 Hi-VHF Offset-Cross FD's - 2TL=3QWL Azimuthal Patterns at 207 MHz	enlarge 332KB, 1024x1024 11 Hi-VHF Offset-Cross FD's - 2TL=3QWL Azimuthal Patterns at 216 MHz	enlarge 161KB, 534x1024 12 Hi-VHF Offset-Cross FD's - 2TL=3QWL Length = 34-in, Width=2-in Side View [1 small box = 2.5-inches]
enlarge 343KB, 1024x1024 13 Hi-VHF Offset-Cross FD's - 2TL=3QWL Circular Polarization Patterns at 174 MHz	enlarge 350KB, 1024x1024 14 Hi-VHF Offset-Cross FD's - 2TL=3QWL Circular Polarization Patterns at 180 MHz	enlarge 343KB, 1024x1024 15 Hi-VHF Offset-Cross FD's - 2TL=3QWL Circular Polarization Patterns at 186 MHz
enlarge 340KB, 1024x1024 16 Hi-VHF Offset-Cross FD's - 2TL=3QWL Circular Polarization Patterns at 192 MHz	enlarge 341KB, 1024x1024 17 Hi-VHF Offset-Cross FD's - 2TL=3QWL Circular Polarization Patterns at 198 MHz	enlarge 345KB, 1024x1024 18 Hi-VHF Offset-Cross FD's - 2TL=3QWL Circular Polarization Patterns at 204 MHz
enlarge 345KB, 1024x1024 19 Hi-VHF Offset-Cross FD's - 2TL=3QWL Circular Polarization Patterns at 210 MHz	enlarge 342KB, 1024x1024 20 Hi-VHF Offset-Cross FD's - 2TL=3QWL Circular Polarization Patterns at 216 MHz	enlarge 436KB, 1024x1024 21 Hi-VHF Offset-Cross FD's - 2TL=3QWL Circular Polarization Patterns - Ani-Gif
enlarge 30KB, 791x1024 22 Hi-VHF Offset-Cross FD's - 2TL=3QWL Length = 34-in, Width=2-in 4nec2 File

Select All.

Sign the Guestbook. There are no entries.