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HF PORTABLE INVERTED L ANTENNA

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 consist of a simple long wire antenna, counterpoise arrangement, a 1:9 Voltage Unun or 1:9 Voltage Balun and an auto-tuner provides access to all HF bands.

The portable supporting mast is a 7m squid-pole and the antenna is a simple 18.7m length of light weight wire. Several other wire lengths are also used including but not restricted to a 25m and 38m lengths in this configuration. The lengths are determined by lengths that avoid 1/4 wavelengths and multiples of this length for al intended operational bands with particular attention of maximum avoidance of 1/4 wavelengths and multiples for the lower bands to be used.

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

Figure 1 shows a typical 1:9 Unun connection with the inverted 'L' antenna and this works fine however having a common ground as part of the antenna is difficult to block common mode currents even with an additional choking Balun. When using this arrangement with my camping trailer of which the ground is the frame of the trailer there is a lot of noise picked 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 that performs as well as the figure 1 arrangement and has the additional advantage of better isolation of the antenna and feed-line particularly when a chocking balun is also included in the feed-line before the connection with the 1:9 balun. The only draw back is that a longer counterpoise may/will be required on the lower bands. It is recommended that the addition of a common mode choke is used to achieve the best results with this antenna arrangement.

The figure 1 arrangements main advantage is that it can be set up quicker and the trailer frame is a sufficient ground when running out a separate counter poise wire is not practical. 

Figure 4 and 5 show SWR and impedance measurements made 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

 

Antenna Length (m)

Counter poise (m)

Note
18.7M 5MCP 18.7 5.0
25M 8MCP 25.0 8.0
25M 8MCP FN 25.0 8.0 Counter poise also grounded to a long steel fence
38M 18.7MCP  38.0 18.7

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

 

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

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

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.

  

BAND
FREQUENCY MHz

SWR for various Inverted L antenna

18.7M 5MCP 25M 8MCP 25M 8MCP FN 38M 18.7MCP 
1.85 21.0 15.5 3.2 6.6
3.60 11.9 1.6 7.8 4.4
5.4 8.5 2.6 11.2 2.7
7.15 4.8 1.8 6.0 2.0
10.10 3.3 6.4 1.9 3.8
14.15 4.8 1.9 1.4 2.2
18.1 2.4 2.4 4.6 1.5
21.2 1.6 2.6 2.8 2.3
24.95 3.3 1.5 1.8 1.6
28.5 1.9 2.5 3.0 1.3
29.5 2.4 2.1 2.2 1.5
50.50 1.5 1.4 1.6 2.7
53.00 2.8 3.0 3.3 2.8

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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Page last revised 31 January, 2022
 

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