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.
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This kit will help reduce or eliminate:
1. Radio Frequency Interference (RFI) to electronic devices including instrumentation and GPS systems.
2. RFI from other electronic devices such as switching power supplies, LED instrument and cockpit lights, battery chargers, GPS and computer systems which generate common mode currents on your radio interface or coaxial antenna feed lines.
3. These filters help reduce SWR problems between transceiver and antenna. The DC power line filter helps keep common mode current out of the power line which could cause interference to other devices connected to the same power source.
These chokes use a ferrite core material that is effective in suppressing RFI from transmitters and receivers experiencing a high noise floor in the 1-300 MHz range.
The ferrite split bead filters are easy to use, don’t require modification of the protected equipment and work in almost all cases, even when plug-in filters fail.
Kit Includes 2 noise reduction split bead (they snap on like a clam shell) filters for coax and AC/DC power/ standard 15 Pin connector cable. 3/4" whole ID - just wrap 2-3 turns of coax cable thru 1 bead and 2-3 turns of the DC power/15 Pin cable thru the other split bead. Does not affect signals carried by the cables, only the common mode interference noise is suppressed.
For additional RFI suppression, use a feed line choke at the antenna feed point to suppress common current on the coax feed line during TRANSMIT and a CMNF-500-50 coax noise filter at the radio end of the coax to reduce common mode noise during RECEIVE.
If you use a linear amplifier use a Palomar Engineers amplifier RFI kit for additional RFI interference suppression.
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Note: A120 radio pictured NOT included.
