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 audio/video systems, computers, telephones, garage door openers, alarm systems, and home appliances, in your house or your neighbor’s house.
2. RFI from other electronic devices such as switching power supplies, LED and fluorescent lights, battery chargers, Ethernet cables, solar systems, kitchen appliances, and cable/satellite TV systems which generate common mode currents on your radio cables.
3. These filters help cure SWR problems between transceiver and a linear amp and between transceiver and antenna tuner or direct to 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 filters 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. DC filter effective for .15-10 MHZ and CMNF-500-50 effective from 1-60 MHz range. Snap on filters effective from 1-300 MHz.
The ferrite split beads and ring 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 a low frequency noise reduction ring filter (works great on DC switching power supplies too!) for AC/DC power, 4 snap on filters (1/2" ID) for I/O cables and the CMNF-500-50 coax noise filter and double male barrel connector for direct attachment to your radio antenna connector. The CMNF-500-50 provides up to 38 dB (6 "S" units) of common mode noise attenuation. Snap on ferrites may be either 4 or 6 sided depending on inventory - they have identical electrical properties..
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For additional RFI suppression, use a feed line choke (like the MC-1-500 for 500 watts or the MC-1-3000 for powers up to 3KW PEP) at the antenna feed point to suppress common current on the coax feed line during TRANSMIT.
If you use a linear amplifier use a Palomar Engineers Amplifier RFI kit (part# RFI-LA-GAC) for additional RFI interference suppression.
Icom 7300 RFI Kit Flyer Download (not available on eBay)
