11 METER HORIZONTAL LOOP ANTENNA
- MATERIALS NEEDED -
50 ohm coax
75 ohm coax
40 feet of wire
To calculate the length of wire needed for a 11 meter loop antenna, we must use a formula. Divide 1005 by Frequency in Mhz will give you length in feet. For example, if we wanted our loop to receive on 27.555 Mhz we would divide 1005 / 27.555 = 36.47 feet or 36 feet, 6 inches.
Before we attach the wire loop, we need to put a matching section of 75 ohm RG-59 coax, between the loop and the 50 ohm coax. The matching section of coax will be a quarter wavelength of the operating frequency. To get this we calculate 246 divided by frequency. In this case it's 246 / 27.555 = 8.93 feet. 9ft. Now we need to figure the "Velocity Factor" of the 75 ohm piece of coax. The velocity factor of your coax is .66 or .80. Most 75 ohm RG-59u coax is .66, so we will use that. Now take that 8.93 feet from above and multiply that by .66. For this purpose the answer is 5.89. Or 5 feet ten inches. The matching section of 75ohm coax is five feet ten inches.
PUTTING IT TOGETHER
Attach 36ft, 6 inch loop wire to one end of 5 foot ten inch piece of 75ohm coax. Put one end of the wire on the shield (braid) of the coax and the other end of the loop on the center conductor of the coax. Insulate connections so they do not touch each other.
Now attach the other end of the 75 ohm coax to the 50ohm coax that goes to your radio. Attach the two ends together as you would repair a cut coax. The 50 ohm coax can be any length.
Now hang the loop horizontally between some structures. Hang it flat / parallel with the earth. Put it as close to a circle you can get it, although it will work fine as a square, odd shaped rectangle or even a triangle. Just getting it up in the air 15 feet will produce significant results no matter what shape is used. Make sure the wire used for the loop is hanging in free air, insulted from everything except the string it is hanging on. Never hang a loop near power lines.
I used thin thread 22-28 gauge wire for the loop and 15 pound fishing line, to hang to loop between 2 trees and one side of my house. It's virtually invisible.
PERFORMANCE - DX stations key on local stations down the street. The SWR is flat, but there is very little noise floor. It sounds like the antenna is unplugged, until a DX station sounds in with full quieting audio. Unlike noisy vertical cb antenna operation, this is static free listening. There is no hash and trash with this horizontal loop. There is little or no DX signal noise floor. This transforms the sound of the DX cb radio traffic, in to a classic 'WW2 military radio' like atmosphere. Everything is quiet unless someone important speaks. The distant heterodyne has that classic, surreal, air raid like sound. One might describe it as sounding like aircraft radio with louder microphones. It's a completely different world of radio. Very pleasing to the ear. Old school sound.
Putting antennas higher in the air is always good, but, in the case of using this horizontal loop antenna, it's performance is amazing when mounted 20 feet or less above the ground. It's performance was amazing when it was laying on the ground. Terrible local reception / amazing DX reception. Hands down this is the best 11 meter omni DX antenna, for SWL only use.
WARNING - Every loop antenna is coming down sooner or later. Most sooner than later. They come down every year or two. This why I deem it logical to build this loop - set to fail. Use light materials that can easily be replaced every year or two.
Special thanks to Matt 26SD782, who introduced me to this antenna years ago.