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.
After many requests we have created a compact, special balun for single band loop (Sky loop or Delta loop) antennas. The CB-2.25-1500 is a CUBE(TM) enclosure containing a multi-core, broadband 2:25 impedance transformer (50 ohm coax input to 112.5 ohm balanced output) in series with a 1:1 current balun for extra common mode current choking to keep RF current off the outside of the coax braid and on the antenna where it belongs. The extra choking action also means that the coax feed line will not act as a radiator causing unnecessary RF interference (RFI). Rated for full 1500 watts PEP and 450 watts CW (ICAS). 1.8Mhz – 61 MHz.
CB-2.25-1-1500EB is housed in a 4” x 4” x 2” waterproof housing with SO-239 input and stainless steel eye bolts on the side for ease of connection to your wire antenna. Top eye bolt acts as an antenna hoist. Also available with top studs for post or wall mounting (Model # CB-2.25-1-1500TS)
Loop antennas should be cut for 1005/F(MHz) in total length, where F (MHz) is the lowest frequency to be used. For 3.5MHz this equates to 288 foot perimeter (square, delta, multi-side ok).
Production Note: These hybrid baluns are special order and made to order for each customer. Please note that shipping will be approximately 2-3 weeks after order placed depending upon our existing production schedule.
Pictures show 2-1 balun but you will receive the 2.25:1 balun with 1:1 hybrid in a single enclosure.
