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.
1/2″/12.7mm max Cable Size Chokes
Model SLO-1/2 family of chokes are for use with ½” coax cable like RG-8, RG-213, 9913, LMR-400 and similar cables up to ½” diameter – works on all cable impedances (50, 62, 75, 90 ohms etc). 80-6 meters.Choose SLO-1/2 (5 beads) or for extended choking, choose SLO-1/2E (10 beads) or for super extended choking choose SLO-1/2SE (15 beads).
Each additional 5 beads is approximately 6 dB of common mode rejection (also 1 “S” unit of noise reduction).
Select chokes with minimum of 500 ohms at your frequency of interest for best results or upgrade to our CUBE(TM), or MC-1-3000 Maxi-Choker(TM) chokes up to 10,000 ohms choking.
Select 5 bead version for 80-2 meters use; 10 bead version for 160-6 meter use, 15 and 20 bead version for even higher choking power on 160-20 meter frequencies. Power rating is same as coax cable used power rating.
Snap On and Slip on Feed line chokes available in sizes to fix cables with outside diameters of 1/4", 3/8", 1/2", 3/4", 1" - check website for other size options.
The 5 bead, 1/2" model was previously part # BA-8
Testimonial:
KI7AY
Wanted to let you know that I was having a problem with RFI on 40m, but immediately after installing your Slip On Coax Feed Line Choke -1/2"/12.7mm cable, 1.8-300 MHz on a new RG-213 jumper between the IC-9100 and tuner, IT WENT COMPLETELY AWAY!
