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” End Fed OCF Antenna Matcher - 100/500/1500 Watts PEP/Digital
The key to end fed OCF antenna success is the matching network interface between the wire antenna and the feed line choke on the coax. Palomar Engineers employs a dual port ferrite matching system that offers wide bandwidth (1.8-61 MHz), and a 100 watt PEP power rating.
The antenna can be used as a sloper, “L” with a vertical section and a longer horizontal section, or as a horizontal or sloper antenna between two trees or supports. Great antenna for portable operations like NPOTA, SOTA, Field Day, etc., or for permanent installations like installing in an attic, under the eaves of a house, along a fence, etc. This is a short, effective and easy-to-hide antenna which gives a good account of itself on -80-6 (95' wire), 40-6 (55' wire) or 20-6 (25' wire) meter bands.
We sell the Bullet-4U-100 separately so you can add you own wire type and length (see table of suggested lengths below) or you can purchase a complete antenna system including wire and end insulator. Remember you also need a feed line choke like the easy adjustable snap on SOFLC.
Use a good quality 50 ohm cable such as RG-8X or similar as that size allows multiple (5-6 recommended) turns thru the feed line choke. The Bullet-4U-100 matching unit is rated for 100 watts PEP for SSB and 100 watts for CW/FT8. If the matching unit becomes warm to the touch after transmitting at high power, reduce the power output or the internal matching unit may become damaged.
NOTE: We rate our Bullet baluns (and ununs) VERY conservatively with a 50% duty cycle as used with digital (FT8) modes. 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 products to theirs and you will know we put much more into our products so you don't have to worry about power saturation failure at a critical moment.
