In this article I will describe how I built my version of the 6m Delta Loop Antenna for use with a 6m Beacon. But first let's look at some information relating to the Delta Loop Antenna.
- A delta loop antenna is a high-efficiency, full-wavelength, triangular-shaped wire antenna known for low-noise, excellent DX (long-distance) performance, and low-angle radiation. It is typically fed with coaxial cable using a 4:1
balun or a 75 Ohm Quarter-Wave Transformer for impedance matching, configured with one apex up or down, and
can be horizontally or vertically polarized depending on feed point
placement.
- Structure: A full-wave loop (total length in meters = 306 divided by Frequency in Mhz ) formed into a triangle.
- Versatility: It can be configured as apex-up or apex-down, or even laid flat (horizontal) for NVIS (local) communication.
- Polarization: Feeding the antenna at a corner or the bottom side generally results in vertical polarization, ideal for DX. Feeding it at the center of the base can produce horizontal polarization.
- Performance: Offers low-noise reception compared to dipoles, making it ideal for urban environments.
- Impedance: The feed point impedance is roughly 100-200 ohms, often requiring a 4:1 or 2:1 balun or 75 Ohm quarter-wave transformer for a 50-ohm match.
- Multiband Capability: Can be used on harmonics with a tuner, though it is fundamentally a single-band antenna.
A Delta Loop antenna is quieter, providing roughly 2–3 dB more gain than a dipole, and offering excellent, low-angle radiation for DX (long-distance) contacts. They are versatile for mounting, often requiring only one high support point, and are less sensitive to ground quality than vertical antennas.
- Lower Noise Floor: Because they are closed loops, they are much quieter and less susceptible to environmental RF noise compared to open-ended antennas like dipoles or verticals.
- Superior Gain and Performance: Delta loops offer higher gain (roughly 2-3 dB) compared to a standard dipole. They function effectively as stacked, bent dipoles, especially when oriented vertically.
- Excellent for DX (Low-Angle Radiation): When vertically mounted, they produce a low-angle radiation pattern, which is ideal for long-distance communication.
- Easy Installation: They generally only require one high support point (such as a tree limb or mast) to hang, making them easier to deploy than horizontal loops or complex beam antennas.
- Wide Bandwidth: They are typically broad-banded and often allow for operation across a wide SWR range without a tuner.
- Versatile Polarization: Depending on where they are fed (top, bottom, or side), they can provide either horizontal or vertical polarization.
- No Radial System Required: Unlike traditional vertical antennas, a delta loop does not require a complex, extensive ground radial system.
- Multi-band Potential: A single full-wave loop can be used on its fundamental frequency as well as higher harmonics, increasing its versatility.
Key Disadvantages of a Delta Loop if not installed correctly:
Delta loop antennas, while efficient, have several disadvantages, including requiring significant height and complex, multi-point support structures. They are generally limited in multi-band performance and can be very narrow-banded, making them less versatile than other antennas. Additionally, they are highly dependent on ground height for optimal, low-angle performance.
- Complex Installation: They require more involved installation compared to dipoles, demanding a tall, sturdy support structure.
- High-Angle Radiation/Limited DX: If not placed high enough (ideally at least a 1/2 wavelength above ground), they can favor high-angle, NVIS (Near Vertical Incidence Sky-wave) propagation rather than the low-angle radiation needed for long-distance (DX) communication.
- Narrow Bandwidth: They often have high-Q, resulting in a very narrow operating bandwidth, which can limit performance outside of the designed frequency.
- Limited Multi-band Performance: While they can work on harmonics, their performance, impedance, and radiation patterns can become unpredictable, making them less ideal for multi-band use.
- Large Size & Wind Load: They are physically large, increasing wind loading and making them more susceptible to weather damage.
- Impedance Mismatch on Harmonics: Their feed point impedance can swing wildly on frequencies other than the primary design frequency, requiring a good antenna tuner.
In any project one needs a plan, diagram, guidelines and information. At least that is my way of constructing any DIY Project. I research the project thoroughly before I start any work. I did exactly this before I started on this project.
Now the Internet is your friend but can also be your enemy if you just jump in and start constructing the first plan you find. I was looking for the dimensions of a DIY 6m Delta Loop Antenna and ran into an abundance of information which included a calculator.
The dimensions for the antenna was calculated using the free Calculator program available HERE ). I set my frequency to 50.000 MHz as this antenna needs to resonate in the 6m CW beacon frequency allocation section. The resulting calculations is shown in Image 1 and 2 below.
Image 1 and 2 (Click for larger view.)
The calculator was fed with the information to the left of the antenna drawings above. Needless to say my dimensions differ slightly from those provided by the calculator. This is mainly due to several inputs that changed due to the way I constructed the antenna and also the parts I used. The calculator however provides good information when building a Delta Loop Antenna. I decided to use the good old antenna formula to calculate the dimensions of the antenna I constructed.
Image: Final calculator measurements (Click on image for larger view.)
Formula for full-wave loop antenna:
Full-Wave in Meters = 306 / Frequency in MHz
6.12 meter = 306 / 50.000 MHz
6120 mm = 306 / 50.000 MHz
Formula for Impedance Matching Transformer:
Quarter-wave matching section length in Meters = 75* cable's velocity factor / frequency in MHz
99 cm = 75 x 0.66 / 50 000 MHz
990 mm = 75 x 0.66 / 50 000 MHz
Materials that I used:
Building the Antenna:
My final dimensions is listed in the image below:
I am not going to go into detail how I constructed my version of the antenna. I will however describe my findings in constructing and testing the antenna. The images below provide good detail of how I constructed the 6 m Delta Loop Antenna.
My build observations and findings:
Pointing Up or Down: The Delta Loop can be orientated so that it is pointing up or down. The advantage of having the apex at the top is that it may be be more mechanically secure as the antenna hangs from a single point. The advantage of having it pointing down as in the diagram above is that it means the maximum current part of the antenna is slightly higher above ground level.
Mast Material: The support for the Delta Loop should be a PVC or Glass Fiber pipe or a similar material. A metallic mast running through the center of the Delta Loop will probably de-tune it.
Feed point impedance and coaxial matching section: The feed point impedance at the design frequency is about 100 ohms, so full wave loops are often fed with an impedance-matching section made from a piece of 75 ohm RG59 coaxial cable, one quarter wavelength long.
Length of an impedance-matching section with 75 ohm cable with a velocity factor of 0.66: The most important thing with the matching transformer is the length of the shielded part. It must be 990 mm long. Here is how I cut the transformer cable (RG59). Cut a piece with a length of 1050mm and remove 30mm of the PVC-coating from each end. I then wound the braid together and remove the small piece of isolation from the center. I tinned the wires and then constructed the "dummy balun" from 40mm PVC pipe and end caps plus a few screws, washers and bolts. See images below of how I built the matching transformer.
The wire for the loop is simple 2 mm PVC coated wire used in household electrical wiring. Each end of the antenna is fitted with an electrical eye lug that is screwed to the matching transformer.
The antenna is horizontal polarized with a final SWR of 1.15 : 1 @ 50 Ohm Impedance. The antenna wire is adhered to the PVC pipe and top apex by means of cable ties.
The antenna is not yet at it's optimal height. I am waiting for my son to assist me in adding the second mast section to bring the antenna to a height of at least 9 meters. This article will be updated with images when I extended the mast length.
The wooden dowel is kept in place by 3 Stainless Steel Self Tapping Screws while the matching transformer is kept in place by 3 cable ties.
The two nylon lines running downwards towards the mast is to keep the 25 mm PVC pipe secure during strong wind storms. You need not install these but where I live we experience gale force winds from time to time.
Preliminary Tuning Result: 1.37 : 1 SWR @ 49.9 Ohm Impedance
Final Tuning Result: 1.15 : 1 SWR @ 50 Ohm Impedance
Good enough for me!!
Use of the 6m Delta Loop Antenna:
This antenna will be used for the 6m CW Beacon that are in the final stage of construction. More on this in a future article.
Finally:
The 6 m Delta Loop is a pretty easy antenna to construct and most of the material can be obtained at a local hardware store. It's an easy way to get an antenna with a small amount of gain well above ground level.
Images (Click on images for larger view.)
