Sloping 40 Meter Delta Loop

Having reached the point where I want to make a serious effort to work DX on 40 meters since the higher bands at this point in the 11 year solar cycle are in such poor condition I decided to upgrade the antenna used for 40 from an elevated Hustler 6BTV about 15 feet above ground level to a self contained vertical – a Delta loop. I had used the Hustler for many years at the current and previous QTHs and was satisfied with it’s performance suiting my needs. When I installed it at the current QTH it was impossible to get a symmetric elevated radial field beneath  it because of our lot dimensions and lay out yet still for occasional contesting and DXpedition work it did OK, also the higher bands were in much better shape plus a tower with tribander Yagi had just been installed allowing for plenty of DX.

After reading some research done by L. B. Cebik, W4RNL SCVs: A Family Album and Doug De Maw W1FB and Lee Aurick W1SE The Full Wave Delta Loop at Low Height October 1984 QST available to ARRL members at the arrl.org website I decided on installing a sloping delta loop to be my 40 meter antenna.

Loops are self contained verticals – class of antennas is noted for its ability to provide low-angle, vertically polarized radiation without need for a ground plane. Having only one good antenna support on the property a tower I chose to use a delta loop with the apex mounted to the top of the tower standoff arm and to produce vertical low angle polarization to feed the antenna in one of the base corners. Delta loops can come in two forms, the equilateral and the right angle delta the equilateral having all side sides the same length while the right angle’s base is longer than it’s two sides. The type of Delta loop I am going to talk about here is a right angle Delta which is somewhat shorter than the equilateral being approximately 32 feet tall while the equilateral is around 42 feet tall. The right angle delta generates slight more gain than it’s equilateral cousin and the shorter height makes it an easier install for those amateur operators with limited height supports. In modeling the right angle delta over average conductive soil with the base at approximately 5 ft above ground the radiation take off angle peaks at 25 degrees above ground – a very nice take off angle indeed for working 40 meter DX from such a simple antenna! To get the same signal take off angle using a horizontal dipole or doublet that antenna would need to be at least 65 feet above ground.

Prior to my having the brain surgery I always built my own wire antennas but now with my construction abilities especially soldering limited I chose to buy a commercially built delta loop. After researching it was determined that Hypower Antenna Company offered delta loop antennas in their product line up and the review ratings on eham.net for their products were very good. I was surprised to learn that Hypower Antenna Company only accepts orders and payment for products by USPS mail, so the order form was printed out, a check written and mailed to the company another pleasant surprise was receiving a call from Dean from Hypower inquiring how I wanted the loop’s feed point set up – balun, coax, ladder line, etc. A few days later the antenna arrived via USPS, inspecting the product it is a very well built antenna – something I would be proud to build.

Full wave loops have a feed point impedance of around 100 ohms on their fundamental frequency (it does vary somewhat in installations) so some form of feed point matching is required for best results. Often that match is a quarter wave matching transformer made from 75 ohm coax that is inserted inline between the coax feed line from station and the antenna feed point but due to my vision impairment I was not able to build one. Though I initially intended to feed my loop with ladder line I ran into issues supporting a low to ground horizontal run of the line so instead I opted for a 2:1 balun made by Balun Design for matching to loops.

Once everything was prepared the apex of the loop was hoisted to the top section of the tower at approximately 30 feet above ground then the base corners were walked out to a point in the yard along the fence line where the base is approximately 6 ft above ground so humans and pets can pass beneath it unimpeded resulting in the loop being at about a 60 degree angle to the ground. The easiest solution for permanently anchoring the base corners was to have two metal T posts driven into the ground then the corner insulators tied off. A piece of PVC pipe was used to further support the midsection of the 56 foot long base keeping it above head height.

I have been using the sloping delta on 40 meter FT8 for several weeks now mainly for working DX near sunrise and sunset, the results have been very pleasing with several new countries worked, something that I would not have been able to achieve using the 102 ft doublet at 30 feet. Working JAs and Asia are a regular morning happening, the early evening hours brings regular European, Russian and South American QSOs.  The loop does have about 5db  nulls in it’s azimuth radiation pattern off to the sides of the antenna sort of a broad oval. I have not noticed any ill effect from them in my operations perhaps because the nulls are broad and also the deepest part of the nulls lay along a 90 – 270 degree azimuth, from my QTH there is not much DX from those headings. An operator with the space available can rotate the ends of the antenna so that the nulls face the directions to where there is little DX activity.

I recommend a vertical polarized delta loop for anyone wanting to work DX on 40 meters and below, seemingly a loop cut for the fundamental frequency should also be a good performer on 30 meters though verticals aren’t that great a performers on 20 meters up, usually a horizontal dipole or doublet will win on those bands.

Good DX!

UPDATE:

For several years now I have been wanting an effective 30 Meter antenna something besides a 102 FT doublet at 35 feet. So satisfied with the results gotten with the 40 meter loop I opted to add a 30 Meters Delta loop manufactured by Hy Power Antenna hanging it from an angle aluminum arm attached to the top of the Hazer. It is too soon yet to give a performance evaluation but it does seem very promising have already worked Argentina and Chile on FT8 running 50 watts to the antenna. Stay tuned!