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.
New improved version now goes down to 100 KHz and up to 61 MHz < 2:1 SWR!
The Bullet-2B is a multi-core balun with a compact enclosure (looks like a bullet) enclosure that is lightweight and easy to transport for your portable loop antenna solution. Halyard hoist at top of balun for convenient attachment point. Input is via SO-239 coax connector and output with side eye bolt output. Rated 500 Watts PEP Watts from .1-61 MHz. DC grounded to coax shield for static bleed off.
This transformer requires a feed line choke at the balun to isolate the coax feed line from the antenna. A coax noise filter is also recommended at the radio end of the coax..
Loop Antennas
Loop antennas are some of the best radiating and receiving antennas you can make. They can be in a triangle (called a delta loop), square or rectangle or even a circle. Horizontal loops can be fed anywhere that is convenient. Vertical delta loops(circumference length=1005/f(Mhz) are best fed 1/4 wavelength (length=246/f(Mhz)) from the top point down one side.
We offer pre-configured loop wire kits for your antenna building convenience. Just choose the band you need - see related products.
Want multiple bands from a loop antenna, consider the 4;1 Bullet (Bullet-4BEB in 500 or 1500 watts versions).
NOTE: We rate our Bullet baluns (and ununs) VERY conservatively at 500 watts PEP with a 50% duty cycle. Some manufacturers selling low cost baluns may use a 5% duty cycle for their PEP rating to make it appear you get a higher rated balun for a lower price, but you may in fact be getting be getting less. Their 1500 watts PEP really means 75 watts continuous or 150 watts at a 50% duty cycle compared to our 250 watts at 50% duty cycle. Our baluns typically cover a larger frequency range under 2:1 SWR which make your transceiver happy and probably will last longer with less electrical stress.
Remember we over engineer our products, to out perform our competition - just compare the weight of our baluns to theirs and you will know we put much more into our products so you don't have to worry about failure at a critical moment.
