40m Delta Loop

This is my 40m Band Delta Loop design that I used when I lived in France (F5VKM). Like all my other Delta Loop antenna designs it’s super quiet on receive, has a relatively low angle of radiation and presents a 50 Ohm impedance at the feed point. Being easy to build, easy to erect and very easy to connect to any transceiver, this antenna is great for the home-brew radio enthusiast.

40m Delta Loop Wire View

The antenna consists of a single piece of wire 44.4958m long that’s arranged into a flattened triangle. Wire 1 (Long horizontal wire) is 20.2m long and exactly 1m above the ground. Wires 2 & 3 are 12.1479m long with the peak being at 7.75m above the ground.

The antenna is fed in one of the lower corners via a 1:1 Balun. This gives the best balanced feed and provides a great impedance match to 50 Ohm coax. No ATU is required with this antenna making it ideal for portable operations. The antenna can be fed directly by coax if you don’t have a balun but, I highly recommend you make a balun yourself as they are really simple to put together.

With the antenna arranged as detailed above it presents a very usable SWR curve.

40m Delta Loop SWR Plot

If you want to move the SWR curve lower in frequency then all that is required is to lower the entire antenna by 25cm. This will move the point of resonance down in frequency. The same applies if you want to move the point of resonance up in frequency, just raise the antenna by 25cm or more depending how far up the 40m you want to go. The bottom wire must always be horizontal regardless of distance from the ground.

Moving the antenna up and down will alter the maximum radiation angle slightly but, not enough to worry about.

40m Delta Loop 3d Field Plot

The 3d Field Plot is very similar to all the other Delta Loop antennas I’ve designed with the deep null in the centre. Once again if you’re looking to work local stations then use a dipole as it will be much better for NVIS radiation, this antenna design is aimed more at the DXer.

40m Delta Loop Elevation Field Plot

A maximum gain of 1.5dBi at 26 Deg is available with this antenna. It’s not a huge amount of gain but, with the antenna being so quiet on receive it’s great for weak signal operations.

40m Delta Loop Azimuth Field Plot

The azimuth field plot shows the bulk of the radiation is through the loop so it’s important to think about direction when erecting the antenna. This antenna is great for working ZL/VK if setup to beam north/south from Europe.

Summary:

Total Wire Length: 44.4958m
Horizontal Wire Length: 20.2m @ 1m above ground
Diagonal Wire Lengths: 12.1479m
Wire Dia: 2.5mm
Height at Centre: 7.75m
Feed Type: 1:1 Balun in bottom corner (Can use coax if necessary)
Impedance: 50 Ohm
SWR: <1.5:1