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.
50:250 ohm (5:1) CUBE™ Unun™, 1.8-61 Mz, 1500 Watts, end fed, vertical
Model CU-5-1500EB- 5 to 1 Unun
(SO-239 in/Eye bolt hoist with output connector on top, side stud for ground/counterpoise)
Purpose. This unun is designed to match 250 ohms unbalanced to 50 ohms unbalanced up to 1500 watts PEP power from 1.8-61 MHz. It provides conversion from unbalanced 50 ohm coax to an unbalanced 250 ohm load/antenna feed point and gives a 5:1 impedance step-up to reduce VSWR on the coax feed line. The unun is housed in a 4” x 4” X “2 NEMA weather resistant box with SO-239 coaxial input and a ¼” stud terminal with wing nut on the top for output and another on the side for ground or counterpoise connection.
This unun is DC grounded and will bleed off static electricity but it is NOT A LIGHTNING ARRESTOR.
Model CU-5-1500 is a 50 ohm to 250 ohm (5:1) voltage unun used to translate a 50 ohm input up to 250 ohms at RF power levels up to 1500 watts PEP (30% duty cycle) when used with a matched load. With a matched 250 ohm unbalanced load SWR should not exceed 2.0 over the frequency range 1.8-61 MHz.
Application. For traveling wave, end fed or portable 20-31 foot vertical antennas the 5:1 balun makes a good transformer for converting 50 ohm coax to a 250 ohm feed point. If you use the antenna on multiple bands, the feed point impedance may not always be 250 ohms and use of the unun at high (>350 ohms) or low (<100 ohms) will require reduced power input or the unun may have its power ratings exceeded and damage to the unun may occur. The (5:1 conversion ratio will change for loads other than 250 ohms unbalanced.
Typical Antenna System Using CU-5-1500
Use a coax noise filter to reduce noise from any vertical antenna or a line isolator to suppress coax cable braid radiation on transmit.
Likewise Termination Resistor values vary from 500-1250 ohms and we have a good selection shown HERE: