Fast deployable HF portable end fed inverted L antenna (1.8 - 54MHz).

This quick and easy-to-set-up multi-band antenna for portable operations consists of a simple long wire antenna, a counterpoise arrangement, a 1:9 Voltage Unun or 1:9 Voltage Balun, and an auto-tuner, providing access to all HF bands.

The portable supporting mast is a 7m squid pole, and the antenna is a simple 18.7m length of lightweight wire. Other wire lengths, such as 25m and 38m, can also be used in this configuration, as long as they avoid 1/4 wavelengths and multiples of this length for all intended operational bands. Special attention is given to avoiding 1/4 wavelengths and multiples for the lower bands being used.

The use of a 1:9 Voltage Unun or 1:9 Voltage Balun presents a range of impedances to the auto-tuner that are more easily matched than when the tuner is used on its own. I am using a Kenwood AT-50 auto-tuner, which, in combination with the 1:9 unun or 1:9 balun, can easily match all HF bands.

Figure 1 depicts a typical 1:9 unun connection with the inverted 'L' antenna, which works fine. However, having a common ground as part of the antenna makes it difficult to block common-mode currents, even with an additional choking balun. When using this arrangement with my camping trailer, where the ground is the frame of the trailer, a lot of noise is picked up from the portable refrigerator, and the transmitter interferes with the dimmable LED lights.

Figure 2 shows an alternate arrangement using a 1:9 balun with the inverted 'L' antenna. This arrangement performs as well as the figure 1 arrangement and has the additional advantage of better isolation of the antenna and feedline, especially when a choking balun is included in the feedline before the connection with the 1:9 balun. The only drawback is that a longer counterpoise may be required, especially on the lower bands. It is recommended to use a common-mode choke for optimal results with this antenna arrangement.

The main advantage of the figure 1 arrangement is that it can be set up quickly, and the trailer frame serves as a sufficient ground when running a separate counterpoise wire is not practical.

Figures 4 and 5 depict SWR and impedance measurements for various antenna configurations. 

Figure 1  Typical 9:1 voltage Unun with inverted L wire antenna configuration and counterpoise wire. 

Figure 2  Typical 9:1 voltage Balun with inverted L wire antenna configuration and counterpoise wire

Figure 3  Table showing various Inverted L antenna dimensions and general arrangements that have been trialed. 

The 18.7m wire length has been successfully used on all HF bands, although its efficiency is low for the 80m band. The 25m and 38m lengths provide better coverage of the lower HF bands, with the 38m length being well suited for operations on the 160m band.

While the 18.7m wire length antenna in the above arrangements can achieve a match for the 160m band, no attempts to make contact have been attempted.

Figure 4  Table showing SWR presented to the auto tuner. SWR in the vertical axis and frequency in MHz in the horizontal axis for the various antenna configurations.

Figure 5  Table showing SWR recorded per antenna configuration per band. The yellow highlights in the table are indication of the better suited antenna length per band based on efficiency and radiation patterns.

Figure 6  Table showing Impedance presented to the auto tuner, Impedance, Resistance and Reactance in the vertical axis and frequency in MHz in the horizontal axis for the 18.7m wire antenna with a 1:9 Balun.   

Figure 7 MMANA antenna modelling for the 18.7m inverted 'L' antenna showing the radiation pattern for 28.5MHz

Figure 8 MMANA antenna modelling for the 18.7m inverted 'L' antenna showing the 3D radiation pattern for 28.5MHz

Also see  1:9 Unun:  1:9 Voltage Unun

               1:9 Balin: 1:9 Voltage Balun

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