Johnny Pedersen (LA3AKA)
2m/70cm Open Sleeve Vertical dipole
I was playing around with the MMANA Antenna analysis software and wanted to design a 2m/70cm vertical antenna. I tried different antenna models, J-pole, half wave dipoles, Ground Planes …. I then remembered a chapter in the 18. edition of the ARRL Antenna Handbook covering Open Sleeve antennas to make Broad band antennas. I thought that this might be useful for making a dual band VHF/UHF antenna.
The Antenna is planned built using 6mm aluminium rods. According to MMANA this will with a distance of 3.2cm between driven element and sleeve elements give an Feedpoint Impdance of 75 ohms on 2 meter and 50 ohms on 70cm. One nice thing with this antenna is that you get a good gain on 70 cm (approximately 3dB over a g Gain:
Band Gain Takeoff Angle
2 m 6.7 dB 3.9o
70 cm 11.0 dB 1.4o
The Centre Frequencies for the antenna shown is 145 MHz and 435 MHz
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