Loop antennas may be constructed in many forms including horizontal full wave loops in square, rectangle or triangle (delta) shapes. They can also be in the vertical plane and are most often in the same shapes with the delta being very popular as it has both vertical and horizontal polarization. The impedance at the loop resonant frequency is approximately 100 ohms but will very slightly on harmonics. Loops are “quiet” antennas compared to verticals and dipoles and are omni-directional. The also exhibit gain on harmonic bands. Once you try a loop antenna you will know why they are so popular with old timers but still a secret to newcomers. Shown below are some typical designs:
Full Wave Horizontal Loop Antenna (a.k.a Skyloop)
This antenna is horizontally polarized and should be mounted as high as possible but works well at low heights of 10-30 feet. They are quieter than a dipole or a vertical, have a broader bandwidth and will usually out perform a dipole antenna.To determine the approximate circumference in feet of a full wave loop antenna use the formula:
1005/Freq in Mhz = length in feet.
The feed point impedance of a full wave loop antenna is theoretically in the vicinity of 120 ohms and requires a 2:1 impedance transformer (for single band loops or a 4:1 balun to match on multiple bands) with 50 ohm line. You will also need a feed line choke or better yet, just get the Hybrid 4:1+1:1 in a single box.
Vertical Delta Loops
Vertical delta loops can be oriented several way but the most popular is to have the “pointy” end at the top (usually a single support) and the lower horizontal ends just out of reach of humans and animals. Best feed point is 1/4 wavelength (246/f(mhz)) from the top point down one side. Vertical delta loops use the same 2:1 baluns as the horizontal loops or 4:1 for multi-band operation.
The CB-4-1500 balun is a multi-core current balun with an enclosure box. Input is via SO-239 coax connector and output can be top studs (for ladder line) or side eye hooks (2) and top eye hook used as a halyard hoist for supporting your wire antenna. Rated 1500 Watts PEP Watts from 1.8-61 MHz (see SWR graph).
This transformer requires a feed line choke to isolate the coax feed line from the antenna. A coax noise filter at the radio end of the coax is also recommended to reduce coax cable common mode noise.is also recommended.
Useful on these type of antennas:
Dipole, double extended
Dipole, linear load, ladder line fed
Dipole, long, non-resonant
Dipole, off-center fed (OCF)
Dipole, snake type, ladder line fed
Long wire with ground system
Multi-band, remote balun
Useful out to 200 MHZ under 2:1 SWR (see swr graph)
Need a 4:1 and 1:1 HYBRID balun? Check out our CB-4-1-1500/5000 with feedline choke built into same box as impedance transformer for ease of installation!
