UHF Stick Dipole analyzed using 4nec2. Characteristic Impedance of 75-ohms resulted in low SWR near 569 MHz, but Excessive SWR at high and low freqs in UHF Band. [Note that Folded Dipole has much better SWR vs Frequency.]
Three additional images illustrate a Fair to Good 300-ohms match results if the Dipole Length is 20-percent longer: Each Whisker=5.27-in with Gap=0.75in for Total WIDTH of 11.29-in, which is a HALF-Wavelength at 523 MHz (just below middle of the band).
Note that very FAT sticks are needed to minimize SWR throughout the entire UHF Band. Quarter-Inch-Copper-Tubing (QICT) is analyzed here. (Half-Inch was difficult to model in 4nec2.)
======================================= Very Wide Band Frequency Sweeps shows FORWARD Gain continues to INCREASE up to about 4.6 dBi at 1425 MHz, at which point the DIAGONAL Gain in the Clover Leaf Azimuthal Pattern takes over, providing about 2 to 4 dBi up through about 2700 MHz, at which point a SIX-LOBE Pattern results in Diagonal Gain (varies from 35-deg to 45-deg) of about 3-4 dBi PLUS Forward Gain of up to about 2 dBi from 3000 to 3500 MHz.
Note that with Characteristic Impedance of 75-ohms, the Stick Dipole is "Resonant" (i.e. Zimag=0) at about 630 MHz and reaches lowest SWR at not only near 569 MHz in middle of UHF Band, but ALSO near 1775 MHz (3X Higher) and near 3000 MHz (5.2X Higher). This behavior is how a single set of Elements, e.g. R-S VU Series, can be designed to cover both Lo-VHF and Hi-VHF Bands.
Date(s): 14 Feb 2011. Album by holl_ands. 1 - 34 of 34 Total. 9102 Visits.