05 January 2014

YO9IRF station updates

Giving the fact that I had enough spare time the last two weeks, inbetween the little Christmas trip I took back to my home town of Ploiesti and the New Year's Eve party, I had the change to propery get my station back up on the air. Since I moved to the new location in June I didn't really have a proper setup and the few times I got on the air was with some modest balcony antennas.


Click to enlarge

The image above is a Google Earth mock-up of my current antenna setup. The red one is the HF dipole, the blue one is the VHF/UHF vertical and the green lines are the two feedlines.

The HF antenna is a an off-center fed dipole (OCFD) 41.8 meters long; this makes it resonate - when properly installed - on 3.5MHz, but on all it's harmonics also (7MHz, 10.5MHz, 14MHz, 17.5MHz, 21Mhz, 24.5Mhz, 28MHz etc). We usually feed dipoles at the center but due to the current/voltage distribution across the resonant wire, it will present a low (close to 50ohm) impedance only at the uneven harmonics (3.5Mhz, 10.5Mhz, 17.5Mhz, 24.5Mhz etc), while at the even harmonics (7MHz, 14Mhz, 21Mhz, 28Mhz etc) it will present a very large (theoretically infinite, practically a few thousand ohms) feed impedance, wich is very far from out 50ohm feedlines making the antenna unusable due to high feed mismatch.