CB RADIO LOOP ANTENNA
- MATERIALS NEEDED -
50 OHM COAX
6 FEET OF 75 OHM COAX
40 FEET OF WIRE
11 METER FULL WAVE LOOP ANTENNA FOR BASE STATION OPERATION
To calculate the length of wire needed for a Full Wave 11 Meter Loop Antenna, we divide 1005 by Frequency in Mhz, giving us the length in feet. i.e. 27.555 Mhz - 1005 / 27.555 = 36.47 feet.
THE LENGTH OF THE WIRE LOOP IS 36 FEET, 6 INCHES
Install a matching section of RG-59 (75 ohm) coax between the loop and the RG-58 (50 ohm) coax. The length of the matching section will be a quarter wavelength of the operating frequency or 246 divided by frequency. In this case it's 246 / 27.555 = 8.93 feet. Next we need to calculate the "velocity factor" of the piece of 75 ohm coax. Most 75 ohm RG-59U coax has a velocity factor of .66. We take that 8.93 feet and multiply by .66, giving us 5.89. Or 5 feet 10 inches.
THE MATCHING SECTION OF RG-59U COAX IS 5 FEET, 10 INCHES
PUTTING IT TOGETHER
Attach the 36ft, 6 inch loop wire to one end of the 5 foot 10 inch piece of 75 ohm coax. Solder one end of the loop to the outer shield of the coax. Solder the other end of the loop to the center conductor of the coax. Insulate these connections to prevent them from touching.
Attach the other end of the 75 ohm coax to the 50 ohm coax that goes to your radio. The 50 ohm coaxial cable can be any length needed to reach the radio.
Hang the loop horizontally between some structures. It will work fine as a square, odd shaped rectangle or even a triangle.
Make sure the wire used for the loop is hanging in free air, insulted from everything except the string it is hanging on. Mount the loop away from metal objects.
NEVER INSTALL AN ANTENNA NEAR POWER LINES!
I used 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 was virtually invisible.
I seem to remember a textbook suggesting that a full wave loop should be at least one wavelength above the ground. (27Mhz = 36 feet) However, you will be impressed by the DX performance of this antenna if you are only able to hang it 10-20 feet above the ground.
PERFORMANCE - THE 11 METER FULL WAVE HORIZONTAL LOOP IS A DX ONLY ANTENNA
The local transmit and receive performance of the full wave loop antenna is very poor. The local noise floor of the antenna is so low, it nearly sounds as if the antenna is unplugged.
When 'skip' / DX conditions are present the antenna comes alive with strong signals, without the pops, squeaks and high noise floor associated with a vertical antenna.
The nature of the horizontal loop antenna on 11 meters transforms the entire listening experience, making CB radio sound more like a military aircraft / shortwave radio like application. It's lack of static and other unwanted noise drastically improves the audio fidelity of all DX stations. Weaker DX stations sound much more more clear, simply because the noise floor is very quiet.
One of the most interesting aspects of the full wave horizontal loop antenna is it's surreal sounding 5,000+ mile noise floor. For example, when a vertical antenna reception produces a S5 noise floor with seemingly no DX activity, switching over to the loop antenna produces a much lower S1 noise floor, allowing you to hear faint voices from stations that are thousands of miles away.
FULL WAVE HORIZONTAL LOOP VS ANTRON 99
Antron 99 at 30 feet vs full wave horizontal loop at 15 feet. I simply connected both antennas to an antenna switch-box and switched antennas when comparing DX signals.
During instances of short DX, (less than 2000 miles) the performance between the two antennas was fairly equal. Both antennas would show the occasional advantage over the other.
During instances of long DX, (2000+ miles) the full wave loop made the Antron 99 seem like a 'rubber ducky' antenna. Hawaii and Australia were booming in to the loop with S9+ signals, while the same signals were often caught in the high noise floor of the Antron 99.
The loop was the overall winner, specifically because it's signal to noise ratio was always better. For example, if the loop receives a signal at S5, the audio sounds very clear, because the noise floor beneath the signal is only S1. If the Antron 99 receives the same signal at S6, the signal can be hard to copy, because the noise floor beneath the signal is S5.
With the above stated, signal to noise ratio trumps overall signal strength. The better the signal to noise ratio, the more pleasurable the listening experience.
The full wave 11 meter loop antenna is quite broadband. Low SWR from 26 - 28.5 MHz
Back when the last DX cycle was on it's way out, I used this loop to make contacts to Australia, Hawaii, Europe etc. (12 watts SSB)
HORIZONTAL LOOP = POWERFUL INTERFERENCE FILTER
Severe power line noise and other local interference destroys the listening experience. The full wave horizontal loop is very resistant to this type of interference, as well as 'vertical noise' and 'local noise' in general.
The full wave horizontal loop is a great long DX antenna, with good short DX performance.
EVERY HORIZONTAL LOOP ANTENNA IS COMING DOWN SOONER OR LATER
Over the years many of us have learned the hard way, when you install a big loop as if it's never coming down, it will severely damage the antenna and / or mounting points when it inevitably comes down. Wet snow, ice, falling branches etc will bring a loop down, no matter how tough you make it. The tougher you make it, the more ice it gathers.
Thus why I deem it logical to install the antenna in a 'set to fail' manner. Place a weak link in the relative chain of each mounting point, allowing the antenna to fall down in an undamaged state. For example, a piece of sewing yarn will break before 18 gauge wire.
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