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.
Model CB-9-1500 is a 9:1 multi-core, balanced output balun housed in a water resistant enclosure with top stud/wingnuts (TS) or Eye bolts (halyard top hoist, side eye bolts/outputs) used to translate a 50 ohm input up to 450 ohms at RF power levels up to 1500 watts PEP when used with a matched load. With matched 450 ohm load the SWR over the frequency range 1.8 to 61 MHz is less than 2:1 on the coax feed side. Actual SWR is under 1.25:1 from 1.8-180 MHz so very useful for 30-150 MHz also - see graphs for specific details
Features
* Wide Frequency Range 1.8-161 MHz, usable to 180 MHz < 1.25:1 into resistive load
* High Power, 1500 watts PEP (up to 61 MHz)
* Convenient side tab mounting feet
Many designs for BBTD antennas using 9:1 baluns at HFLINK.COM
We also have the 9:1 with the built-in 1:1 choke/balun in part# CB-9-1-1500EB