By Remo – IM0JZJ
For some time, I had been considering the possibility of building a wire antenna for the 40-meter band that would not take up too much space.
An inverted V seemed like a good solution, provided it was installed in the following way, which I have already tested: the driven (hot) element would be horizontal, while the other end would slope down toward the ground, acting like a sloper. The horizontal element would occupy approximately 10 meters, plus another 6 meters running diagonally toward the ground at an angle of about 120 degrees relative to the horizontal section. The resulting installation would occupy approximately 12 × 6 meters.
This arrangement is not bad, but it did not satisfy my desire to develop something more interesting, especially for installations where space is limited, such as a house in a city, a small town, an apartment building, or a property with very close boundaries.
After experimenting with several antenna designs, I returned to the idea of testing and studying the Morgain antenna, exploring alternative construction methods and installation configurations.
The best solution, in terms of shape and footprint, is to shorten its physical length without compromising its electrical design and functionality. This makes it possible to transmit and receive not only on 40 meters but also on 80 meters, since the Morgain is designed as a dual-band antenna.
Performance and SWR Measurements
During my tests, I measured SWR values ranging from 1.2:1 to 1.4:1 on 40 meters.
On 80 meters, the SWR was approximately 1.5:1 at 3620 kHz, decreasing to 1.1:1 at 3640 kHz, a shift of just 20 kHz. It then remained within the measured range up to 3700 kHz, rising again to 1.5:1 at 3720 kHz.
Under these conditions, it is advisable to insert an antenna tuner between the transmitter and the antenna.
For balanced feeding, the antenna should ideally be fed with a balanced two-wire line. When using coaxial cable, the feed is unbalanced, so a 1:1 current balun should be used. The Morgain has a feed-point impedance of approximately 50 ohms.
Installation Setup
My installation consisted of two galvanized steel poles, each extending 11.50 meters above ground, so that the antenna was approximately 10 meters above ground level.
Each pole was assembled from the following sections:
- One 6-meter length of 1¼-inch-diameter pipe.
- One 3-meter length of 1-inch-diameter pipe.
- One 3-meter length of ¾-inch-diameter pipe.
Approximately 30 cm of each section was inserted into the next section. The joints were bolted together, and the assembly was secured in a 2-inch-diameter pipe section partially buried in the ground.
The coaxial cable was RG-8X, 50 ohms, approximately 14 meters long.
The completed antenna occupies approximately 10 × 0.5 meters. The wire required is 32 meters per arm, using 1.5 mm² insulated electrical wire, for a total of 64 meters.
Tests were conducted from my home on the island of Sant’Antioco, southwest of Sardinia, Italy. In both transmission and reception, I obtained signal reports of 59, 59+10 dB, and 59+20 dB across Italy, using only 90 watts of transmitter power.
Antenna Design and Tuning
The antenna described here is a dual-band design for 40 and 80 meters, with a physical footprint of only about 10 meters.
The wire is ordinary vinyl-insulated electrical wire with a cross-sectional area of 1.5 mm², commonly used in domestic electrical installations.
Refer to the accompanying drawings for the construction details, shape, and dimensions.
The dipole consists of two arms, each made from 32 meters of wire. The wire length has been designed to eliminate the two jumpers previously used to tune the 40-meter band.
For operation on 80 meters, however, two jumpers must be installed approximately 1.45 meters from the ends of the antenna, as shown in the drawing.
Before making the permanent connections, use two temporary jumpers approximately 12 cm long, with pins soldered to their ends so they can pierce the wire insulation.
Once the desired resonance frequency has been obtained, solder the jumpers permanently in place.
Materials and Construction
Prepare three wooden boards, each 8 cm wide and 50 cm long. They should be as thin as possible and made from a hard type of wood.
Drill the required holes and protect the boards with marine varnish. I used iroko wood; beech would also be suitable. Spruce is not recommended, even though it is lighter.
The total weight of the three boards in my installation was 400 grams.
You will also need sixteen fiberglass laminate spacers, one approximately every meter. This is the material commonly used for printed circuit boards. If the material still has copper cladding, remove it before use.
Assembling the Antenna
Assembly is not particularly difficult compared with a conventional antenna, but it is important to route the wire correctly through the wooden boards and fiberglass spacers.
Proceed as follows:
- Take one 32-meter wire and attach it to the lower side of the central wooden board. Strip the insulation, tie a knot, and solder the connection. The knot and solder joint provide mechanical security and a connection point for the matching device and coaxial cable, preventing the wire from slipping out of the board.
- Thread four fiberglass spacers onto the wire.
- After approximately 5 meters, route the wire through the lower side of one of the lateral wooden boards, then bring it back through the upper side. Insert another four fiberglass spacers.
- After a further approximately 5 meters, route the wire through the upper side of the central board and continue following the path shown in the drawing.
- Once the first arm is complete, arrange the wire so that all parallel wire sections follow the correct path, as illustrated in the drawing.
- Position the spacers approximately one meter apart and secure them in place.
- Build the second 32-meter arm in exactly the same way, starting again from the central board.
Finally, seal all exposed parts with silicone sealant.
I have nothing more to add. I repeat: follow the drawings carefully.
Good luck with the construction, and best wishes for many enjoyable contacts.
73,
Remo – IM0JZJ