G7FEK Nested Marconi Antenna

G7FEK Nested Marconi Antenna
The G7FEK Nested Marconi Antenna was first designed in 1988 by Mike G7FEK for fundamental frequencies of 3.95 and 6.25 at the request of a friend. The requirement at the time was for a small, efficient, stealthy antenna without the need for an ATU (need I say more!). The designer, now a licensed radio ham, also made a version for himself for the Amateur Bands and it was his mainstay SWL antenna. After the lifting of the Morse Code requirement in the late 1990s, the antenna was used regularly to transmit on the Amateur Bands. Mike had also published the original design on the packet radio bulletin board network in the mid 1990's, generating some minor interest.
The need for small HF antennas has grown since the lifting of the Amateur Radio Morse Code requirement. Mike noticed that most Hams with small gardens were restricting themselves to 7 MHz and higher, using mostly the "1/2 sized" G5RV or Windom-40 antennas. These antennas take up 15 to 20 meters (50 to 66 feet) of space of space respectively, and do not work well on the 80 Meter Amateur Band.
Mike is known for putting out a consistently strong signal on HF using small antennas, and several Amateurs wanted to know more. He decided to make some improvements and run tests to provide an easy to build version, with a view to publishing it on the Internet so that everyone can benefit.
Now there are several versions of this antenna in use. Most of the users are pleased with the results and the ability to use the 80m band with an antenna shorter than a 1/2 sized G5RV. The antenna has proved itself during the sunspot minimum, where some other small antennas have failed to perform well enough. This has recently led to an increase in interest in the design. The antenna has recently been tested with a transatlantic contact, using the same antenna at both ends, between Canada and the UK, on 80 meters and evaluated by the Royal Signals Amateur Radio Society .
The antenna uses two Marconi quarter-wave elements in which the interaction is used to good effect to improve the radiation pattern and provide a radiation resistance averaging 50 ohms. The radiation pattern of the antenna provides both low angle and high angle properties with low angle being dominant. The low angle properties of the antenna provide good DX performance, especially from elevated locations.
How it works
For coupling power, the antenna works on the principle that quarter-wave wire elements are low impedance on their odd harmonics. Thus it is possible to automatically select elements without traps. This principle is also used on the Cobweb and Nested Dipole antennas. The dimensions of the antenna create a small amount of interaction between elements so that the horizontal portion contributes to the radiation. For instance on 7MHz the 3.7MHz element also achieves a small amount of RF current and radiation which combines with the 7MHz vertical. This is because the 3.7MHz section is effectively floating and resonant as a 1/2 wave on 7MHz. This appears to provide a performance improvement over a simple 1/4 wave inverted-L antenna and effective multi-band operation.
Some people confuse the antenna with a Windom Antenna, or off centre fed dipole. These antennas tend to take advantage of the impedance coincidence point on even harmonics of a horizontal dipole antenna and are therefore essentially dipoles. The Nested Marconi antenna is not a dipole, it combines several antenna types depending on the band in use: an unbalanced vertical on low bands; a long-wire antenna on high bands; and on 10MHz it works similar to a Zeppelin antenna as an end fed dipole.
The benefits of the G7FEK Nested Marconi Antenna are as follows:
* Only 46 feet (14 meters) long
* Multi-band operation (Works well on most amateur bands including 80m)
* Can work without an ATU on at least two amateur bands including 80m.
* Unbalanced antenna is ideal for coax feed
* Radiation Resistance is between 25 and 200 ohms on all bands, thus providing easy matching and good efficiency
* Low angle of radiation is dominant (ideal for DX working)
* A Simple counterpoise ground can be used effectively
* Easy to build and install
The official construction guide is available from here: PDF Construction Guide. It is freely distributable within the Amateur Radio community.
There is no known commercial version officially available, as the designer wishes to encourage Radio Amateurs to build their own antennas. It is easily constructed using a standard ribbon dipole centre at the top and a standard coaxial dipole centre at the feed point. 300 or 450 ohm ribbon is used for the vertical section and standard 1.5mm wire is used for the elements.

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