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.
1500 Watt PEP Rated 1:1 CUBE™ Balun for dipoles
* Help keep RF out of the shack.
* Provides maximum transfer of RF to the antenna.
* Suppress radiation from the feeder cable
* Makes the antenna radiation pattern predictable.
* Outperforms the competition by 24 dB common mode rejection! (see graphs)
* Reduces QRN and TVI to the neighbors.
The CB-1-1500 balun is useful as common mode feed line chokes or unbalanced coax to balanced antenna interface. SO-239 input to side terminal/eyebolt output. . Rated 1500 Watts PEP from 1-61 MHz. Common mode rejection up to -38dB over the frequency range. The CB-1-1500 is the balun version and the CU-1-1500 is the unun version (coax in and coax out).
Use as line isolator, antenna interface, or as a common mode choke to keep RF on the antenna and off the outside of the coax braid. Much more effective then our snap on ferrite beads as this balun which provides a higher choking impedance over a broad frequency range.
For most effective results, use another feed line choke (coax noise filter) at the radio. Helps reduce noise floor too by choking off common mode neighborhood noise picked up on outside of coax braid acting as secondary receive antenna
