Vertical Loop Antenna
Consider a Vertical Loop for your next Antenna
Living in a deed restricted community and the confines of those “no antenna” restrictions I still enjoy HF bands. Most of the time I operate on the 20M and 40M bands in CW or digital modes. I found using a vertical full wavelength delta loop for portable operations is a nice improvement over my rather NVIS attic dipole. This lead me to try new loop shapes that would blend into my landscape for long term use. While this loop antenna will not outperform a beam, it is a decent all-around antenna. The main advantage of a loop is the low takeoff angle for DX and the fact that it can be easily matched. The key word is “vertical” as horizontal loops simply do not work very well 10 feet above ground level. In contrast the vertical loop bottom element can be on the ground (but insulated) and still operate with a low take off angle. Do not place the bottom of the loop in the ground. Looking for ways to use a full size vertical loop at home I experiment with any shape that would fit in or around existing structures.
20M Vertical Loop
The length of the loop is always one wavelength and the best shape would be round as a circle has the maximum area for a given perimeter. Knowing loops are constructed in many shapes; round, square, triangles or somewhat irregular depending on the support structures available but there performance improves with more area within the loop. This is why are circular full wavelength loop is preferred but difficult to build. My experience has shown the simple to construct delta loop still produces nice results and became my standard for antenna site selection. The delta is an equilateral triangle with an area approximately 60% of a circle therefore if I can build a loop approaching 60% of the area of a round loop I will have good results.
The criteria for successful vertical loop stealth antennas and related information you should consider are presented with two objectives; the antenna must not be visible from the street and keep the area within the loop big. HOW BIG? The main concern is area so my rational is a delta loop works well at 60% of a perfect circle. So 50% is good and 20% is similar in performance to my attic dipole and not worth the effort. The visibility is a simple issue as smaller is better and limited by RF current and mechanical strength. Using a 100W transceiver #28 AWG is the smallest size before resistance starts to subtract a dB and #20 AWG is mechanically ready for the wind test. You can pick the wire size and color insulation that matches the local environment.
Selecting the shape of the loop will be determined by the location of good supports for the loop. This usually means trees to most people but I have found great success with fences, swimming pool screen enclosures and house walls. The shape of the loop is not fixed by any standard except area inside, my loops have been mostly rectangles or irregular in tall bushes seems work fine. My preference is to loop fed at a corner like a delta. The literature on the feed points indicates the bottom corner of a delta or bottom center of a square/rectangle should produce a lower takeoff angle for better DX. My non-scientific tests of build it and get on the air has not shown any difference with middle, side or 1/3 side feed point. So any irregular looking shape you can construct should work as a real life loop antenna.
When installing a loop around a pool or patio screen enclosure you have some advantages with a large area, small aluminum supports at wide spacing and fiberglass screening. Place the loop inside for low visibility. Any #22 Gauge or heavier wire will handle a 100 Watt transmitter but I recommend #12 AWG THHN to span the 8 to 10 feet between supports and provide high voltage insulation.
Mechanical supports are insulators use for livestock electric fencing painted to match with polymer paint (plastic lawn furniture paint) to ensure dielectric strength. You should have the idea for some locations at your QTH by now. Determine the maximum vertical height available select a loop shape that will work on your site. Next looking at the nine foot example below you can see by quickly scanning the table green is good and red is bad. Invalid just will not fit in the height available.
Vertical Full Wavelength Loop Calculator
The table below is the display from the Full WL Loop Calculator output. The color code is based on my rational that a delta loop works well at 60% of a perfect circle. So 50% is good (GREEN) and 20% (RED) is similar in performance to my attic dipole and not worth the effort. If you had something other than 13 feet available click on;
for a copy of the Microsoft Execel Spreadsheet calculator. Most browswers will open a preview and downlaoad from that window.