My 40 Meter NVIS Square Loop Antenna
By NA4L Dave Newman
This is a full wavelength horizontal loop antenna, "a skywire",
with a parasitic reflector for the southcars frequency.
These pictures above are only showing the feed corners.
As an NVIS experiment, I constructed a 40 meter full wavelength loop antenna with a parasitic reflector cut for the SouthCars frequency, using number 12 insulated copper wire.
Both square loops are horizontal to the ground.
The driven loop has a total wire length of 134 feet, 33 feet and 6 inches on a side, and 27 feet off the ground.
This loop is fed at one of the corners with a coaxial matching transformer made from 21 feet and 10 inches of 75 ohm coax (RG-59 with .66 velocity factor).
The reflector loop has a total wire length of 140 feet and 6 inches, 35 feet and 2 inches on a side, and 10 feet off the ground.
As you can see this makes the spacing .125 wavelength or 17 feet apart, which is spacing for PEAK antenna gain for a two element loop system.
(This array is beaming straight up with about 5 to 6 DB of antenna gain.)
Take a moment and THINK about this...(about one S unit of gain!!).
This antenna system is supported by trees at the corners and is under the canopy of the trees (by arslan at tforge) . However, at this frequency the "tree canopy" does NOT seem to effect the performance of the antenna system.
This antenna will be tested for short distance communication (50 to 400 miles).
This antenna has an omni-directional pattern and being a closed loop antenna circuit, it is very quiet. The tests so far have been very positive.
NOTES: With this feed system, this antenna is a ONE band antenna!
10-29-11: I have found this antenna system to be a super system for day time coverage on 40 meters !!
For questions email Dave at imna4l AT embarqmail.com
(Remove the "AT" and add @ no spaces)