80 METER HORIZONTAL FULL WAVE LOOP ANTENNA
Article and Website By KN4LF (Now NZ4O) in 2008
I decided to publish this website in order to pass on some insights about this antenna that I've garnered through extensive experimentation. A warning though, some of the combined design aspects of the antenna may be unique and unorthodox, a think out of the box antenna design. Note! I do not have a B.S. or M.S. in EE, which makes me a true amateur radio operator not a "professional" amateur radio operator, so some of my antenna theory explanations may be incorrect.
Fortunately I live in a nice quiet subdivision on 1/3 of an acre at an elevation of 218 feet, on the NW slope of a 260 foot hill overlooking a good sized lake with no HOA/CC&R nonsense. Though I'm on a hill I have wetlands on the east and west side of my property, with the surface soil type consisting of black muck underlain by red clay, with a high water table. So this QTH is a pretty good location for vertical antennas.
That was the good news, now the bad. I have seven oak trees on the property and of course there is the house which sit's in the middle of the property. So there is no room for individual antennas on all bands between 160 and two meters. Initially I put up a fan doublet for 80-10 meters and it worked okay but it was nothing to write home to mom about.
So that led to the 80-10 meter horizontal full wave loop. I used the formula of 1005 divided by frequency in mc and chose 3350.000 kc. That makes the single wire element 300 feet in length, with four legs of 75 feet set out in a square and made out of black UV resistant double coated plastic stranded #14 wire. It is fed with 40 feet of high quality #18 gauge stranded hard drawn copper 450 ohm window/ladder feed line and is tuned by a link coupled balanced Johnson Viking Match Box (275 watt carrier/1100 watt PEP). This allows for multi band operation between 80 and 10 meters.
Originally the length of the antenna was 288 feet (3496.527 kc) but the bandwidth was very narrow and tuning on the Johnson Viking Matchbox critical. By lengthening the antenna to 300 feet that solved the critical tuning issue.
Each of the four corners of the antenna are up at 35 feet in oak trees, with each corner pointing NE, SE, SW, NW. The feed point of the antenna is in the middle of the leg that is broadside N-S and up on a Rohn telescoping push up pole. I let the antenna wire float through the four porcelain antenna insulators as the oak trees that they are attached to move around quite a bit on my windy hill.
It is not necessary for the antenna to be perfectly square for good performance. Actually round is best followed by square and then triangular. The four corners of the antenna also need not be at exactly the same height for good performance.
In theory the antenna should be a high angle radiator only on 80 meters with local and regional coverage out to approximately 500 miles. However I have discovered that the antenna also hears and works DX quite well into Europe and Oceania.
Modeling the antenna with EZNEC 5.0 tells the secret. Though the takeoff angle of the highest current point is 90 degrees, at 3 db down the take off angle is 52 degrees, which is low enough for DX operation out to approximately 5000 miles.
On 60 meters performance is similar to 80 meters. On 40 and 30 meters the take off angle is considerably lower. On 20-10 meters the take off angle is very low and there are many lobes that for all intents and purposes makes the antenna omnidirectional.
Per my EZNEC 5.0 modeling, as follows are take off angles of the lobe with the highest current point for each band as well as feed point impedance
80 meters- 90 degrees, 3db down 45 degrees. 65 ohms
60 meters- 90 degrees, 3 db down 44 degrees. 3663 ohms
40 meters- 44 degrees. 275 ohms
30 meters- 35 degrees. 285 ohms
20 meters- 27 degrees. 265 ohms
17 meters- 21 degrees. 400 ohms
15 meters- 18 degrees. 400 ohms
12 Meters- 15 degrees. 370 ohms
10 meters- 11 degrees. 250 ohms
At my QTH does the antenna have nice clean multiple lobes and take off angles as low as modeling says? With three other antennas pretty close by as well as seven oak trees it's doubtful. But I can attest to the fact that the antenna works very well.
On DX, in an A-B comparison between the old 80-10 meter fan doublet antenna and the new 80-10 meter horizontal loop, the loop was always more quiet and most of the time yielded stronger signals both on receive and transmit.
By the way I use the Ladder Lock center support insulator on my ladder/window line fed antenna. It can be seen and purchased at http://www.radiobooks.com/products/llock.htm .
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Visits Since
10/05/2008