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.
The Bullet-6B-500 and SBullet-6B-1500 are multi-core core baluns with a compact enclosure (looks like a bullet) enclosure that is physically lightweight but electrically robust and easy to transport for your portable loop antenna solution or permanent installation. Halyard hoist at top of balun for convenient attachment point. Input is via SO-239 coax connector and output with side eye bolt output. Choose your model rated 500 or 1500 Watts PEP from 1.8-61 MHz.
This transformer requires a feed line choke (see related products) to isolate the coax feed line from the antenna. A coax noise filter at the radio end of the coax is also recommended for best results.
Note" Picture shows 4:1 bullet but 6:1 is identical in size, shape with a different label and impedance level is 300 ohms output. N connector option is custom make for each order - please allow 2 weeks manufacturing time before shipment.
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.
