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.
This ferrrite Multi-Ring/Multi-Snap-On Combo Pack is a convenient solution for troubleshooting RFI/EMI (1-300 MHz) with various diameter cables ranging from 3/8" to 1.4"/35.6mm for use as either single turn or multiple turn RFI filters using ferrite rings and snap ons.
The filters are useful for RF coax, AC/DC power cables, and device interconnection cables.
Always use a snap on or ring with a larger inside diameter than the diameter of the cable and use multiple turns if possible (2 turns through the snap on is the same as 4 snap ons with 1 turn). Included in these combo packs are our most popular snap on sizes as follows:
Combo Pack includes the following:
F240-31 ring – 1.4″/35.6mm ID – 6 pieces
FSB31-3/8 – 3/8″/9.5mm ID – 6 pieces
FSB31-1/2 – 1/2″/12.7mm ID – 5 pieces
Normal Retail price is $112 for these parts
