Broad Band Terminated Dipoles (BBTD), Tilted Terminated Fold Dipoles (T2FD) and Balanced Termination Folded Dipole BTFD) antennas can be designed to cover a large range of frequencies between 1.8 30 MHz. Longer length antennas generally provide better low frequency efficiency but take up a larger footprint of land. One BBTD that has worked well at the AK6R antenna farm is shown below. Many other designs are available and can be found at www.HFLINK.COM as well as other internet sites. Your mileage may vary using this antenna, but as a general coverage antenna for ham and shortwave broadcast, the simplicity can’t be beat even though an individual dipole on a specific band may out perform this broad band dipole. Palomar Engineers has all the parts you need to build this antenna, so why not give it a try?
Depending on the source of the antenna design, different value baluns are specified. Our Bullet(TM) baluns in ratios of 9:1, 12:1 and 16:1 are excellent for this type of antenna as they are broadband from 1.8-61 MHz and will take up to 500 watts PEP.
After many requests we have created a compact, special balun for OCF antennas with vertical radiators. The CB-4-1500ODCV is a CUBE™ enclosure containing a dual core, bifilar wound, voltage balun to force equal voltages on the unequal sides of the off center fed antenna and force current down to the vertical radiator so it acts like a vertical antenna adding to the radiation pattern at low angles for DX.
The vertical radiator is typically 10 feet of 50 ohm coax for the 40 meter long (67 feet at the top) and 22 feet long for the 135 foot OCF.At the bottom of the vertical radiator you should have a line isolator or 1:1 balun (such as the Palomar BA-8E or BA-58E sleeve balun, or CB-1-1500 cube balun) to stop the current on the outside braid of the coax from using the rest of your feedline back to the radio as a long vertical radiator causing RFI and other problems as well as skewing the radiation pattern. The balun can be used with any size.
The balun is rated for full 1500 watts PEP from 1.8Mhz – 61 Mhz and usable to over 150 MHZ! (see graph) The balun can be used with either a 50 or 75 ohm coax vertical radiator and feedline.
The matching line isolator is the MC-1-3000 which should be used at the end of the vertical radiator.
Likewise Termination Resistor values vary from 500-1250 ohms and we have a good selection shown HERE: