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.
Simple AC Power Cord Noise Filter Choke+ Power Cord included
The simplest, most cost effective AC power cord noise filter is a ferrite ring installed as shown in the picture (at the appliance AC input) to stop feed line appliance radiation back into the AC power line or into the radio/appliance to suppress common mode power line noise current on the AC power cord or to suppress common mode noise present on the power lines from degrading the performance of the attached device.
Keeps RFI out of appliances like TV, radios, computers, etc and like wise keeps noise generated by electronic devices from feeding the noise back into the AC power line and affecting other devices plugged into the same lines.
These chokes are cheap, easy solution for RFI issues. Just replace your existing power cord with these pre-wound cables and enjoy interference free operation.
Got your own AC power cable that needs a ferrite ring only? The use ACCF-1.4 ring. This ring also works well on switching power supplies (use 1 on AC input and another on the DC output or just order kit RFI-SMPS).
