About Off-Center-Fed Dipoles
The Off-Center-Fed Dilemma
Few antennas are so controversial as the Off-Center-Fed Dipole
For sure, the OCFD is a 'Wonder' Antenna.
- Some hams find it 'Wonder'ful, claiming good performance on many bands.
- Other hams find it a 'Wonder' that anyone would use this "lousy" antenna.
In other words, some hams swear by it, others swear at it.
Why are the opinions of this antenna so different?
There are, of course, a couple of reasons for the different opinions of this antenna.
First of all, we must realizethat not all OCFD antennas were created equal. There are significant differences in their behavior and performance. This is primarily caused by differences in their BALUN, resulting in Common Mode Current problems. Common Mode Current (CMC) typically causes a multitude of problems. See Next Page: CMC & OCFD .
Second, the OCFD antenna is prone to strong Common Mode Current (CMC) problems. And CMC problems are highly influenced by the environment surrounding the antenna. Some installations are high and in the clear, with nothing near them for 100 meters . . . while others may be erected near the ground and in-between houses. Worse yet, some may have one leg of the antenna running over the house or garage. How heavily the OCFD is affected by all of this depends on the characteristics of its balun. (Most commercial ODFD antennas are pathetic in these cases).
Finally, CMC problems are highly dependent on the output power of the transmitter. When running QRP or even 20 or 30 Watts, the antenna may seem to be perfectly 'clean', but when running 100 Watts and especially high power, it may become a Common Mode Contaminator!
The key to obtaining satisfactory results with this antenna is understanding all of the parameters affecting its performance and optimizing them for your specific and unique situation.
Unless environmental, ("Ugly" above), or impractical ("Bad" above),
CMC problems are almost always due to a poor choice of Balun.
BEFORE continuing with OCFD, it is important to first understand what Common Mode Current is and how it effects all antennas, but ESPECIALLY OCFD antennas.
To: Common Mode Current Page
Continue with Alternatives to OCFD