Sunday, February 13, 2011



11 Meter Loop CB Radio Base Station Wire Antenna

Easy 11meter horizontal loop antenna. DX only. Performance close to 1/2 wave vertical.
Materials needed:
50 ohm coax any length
75 ohm coax
37 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 this loop to our 50 ohm coax we need to put a matching section in between the loop of wire and the 50 ohm coax. This matching section is a section of 75ohm coax.(cable tv coax) To figure the length of this 75 ohm coax This 75ohm section 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 or approximate. 9ft. Now we need to figure the "Velocity Factor" before we cut this 75 ohm piece. The velocity factor of your coax is .66 or .80. Most RG-59u is .66 so we will use that. Now take that 8.93 feet from above and multiply that by .66. For this the answer is 5.89. Or 5 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 that 75ohm coax to the 50ohm coax that goes to your radio. Attach them together just as you would repair a cut coax.

Now hang the loop horizontally between some structures. Meaning flat and 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 strange shape. Make sure the bare wire used for the loop is hanging in free air and insulted from everything accept the string it is hanging on.

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