Mult-band HF portable Inverted L antenna - 7 MHz to 30MHz. October 2025. Under development

Requiring an easily deployable and reliable antenna for portable campsite radio communication, I selected a multi-band inverted L radiator with a 4m counterpoise type radials. This type of antenna offers reliable and predictable performance while maintaining a small set-up footprint. The inverted L antenna uses 13 meter-long elements, covering a frequency range from 7 MHz to 30 MHz with reasonable efficiency and a low radiation angle.

The multi-band inverted L antenna is intentionally designed not to be resonant on any amateur band, resulting in a relatively high feed-point impedance across all intended operating frequencies. The antenna is fed through both a 4:1 balun and a 1:1 choking balun. A length of coaxial cable then connects the system to the antenna matching unit and SWR meter before finally reaching the transceiver.

The 4:1 balun is used to transform the higher antenna feed-point impedance to a level that the matching unit can more easily manage and reduce the higher SWR levels on the connecting coax feed-line. The 1:1 choking balun is employed to suppress common-mode RF currents that might otherwise radiate from the coax and compromise the antenna’s intended radiation pattern and interfere with other equipment..

Fig 1 Shown is the complete portable set up. The antenna's 13m (6m + 7m) Inverted L element (A), the three 6.2m ground-plane radial elements (B), the 4:1 + 1:1 balun hub, 50 Ohm coax cable, antenna matching tuner and the TS-50 radio.

Below is an MMANA-GAL antenna model prediction for antenna load characteristics across the HF band from 7MHz to 30MHz for connection impedance of 200 ohms and by avoiding the high SWR levels for the intended amateur bands the systemis  within the matching range of the antenna matching tuner.  The model shows the load SWR for a direct 1:1 balun, a  4:1 balun and a 9:1 balun match.

Figure 2 MMANA-GAL antenna model prediction of the antenna SWR through a 1:1 Balun (50 Ohm Impedance) and through a 4:1 Balun (200 Ohm Impedance) plus 1:1 balun combination to achieve an easier broadband match and reduce coax cable losses. The vertical axis is the SWR ratio and the horizontal axis is the frequency in MHz. The antenna is mounted to a Squid pole with the feed point being approximately 1.5m above the ground. Also shown is a 9:1 Balun (450 Ohm Impedance) connection that indicates an improved SWR on the coax feed-line for 7 MHz and frequencies above 16 MHz. 

Figure 3 NanoVNA showing the SWR as presented at the 4:1 and 1:1 combination balun. While broadly similar to the MMANA predicted SWR values it appears to be a little better.

Figure 4 Chart shows coax line losses (Vertical axis) for a 10m length of coax at various frequencies at various SWR ratios (Horizontal axis). This chart highlights the importance of a step down balun transformer in reducing the SWR losses on the coax feed-line and where possible in using the minimum length of coax feed-line.

Figure 5 Chart shows coax feedline losses in dB for various lengths of RG58 coax at 7, 14 and 28 MHz. Ideally this should be kept under 2.0 dB. Note that around 3 dB about half the power is lost and this is not including balun and tuner minor losses.

Construction

The Mult-band HF portable inverted L antenna is simply a main radiator 13m in length made from PVC covered 0.75mm2 (AWG 18/19) copper wire. The counterpoise element is 4m in length from the same material. The antenna elements have attachment loops at the ends and all wires have crimp lugs for connection to the balun hub.

The 4:1 Balun Hub is the convenient central hub of the wire ground plane antenna. The dimension are dictated by the the height of the support structure, a 7m Squid pole, not be a resonant length at any amateur band and not being too long at the 10m band as to produce a high angle of radiation.

Photo 1 Shown is the 4:1 Balun Hub for the wire ground plane antenna. The radiator wire element is attached to the left post and the three radiators are attached to the right binding post.

See Balun details: 4:1 Balun Hub that includes a 4:1 transformer plus a 1:1 choke balun to mitigate common mode RF currents from the coax feedline.

Testing and Modelling

Figure 6 MMANA antenna model indicating uniform low angled radiation pattern at 40m.

Figure 6 MMANA 3D antenna model indicating uniform low angled radiation pattern at 40m.

Figure 6 MMANA antenna model indicating uniform low angled radiation pattern at 30m. 

Figure 6 MMANA 3D antenna model indicating uniform low angled radiation pattern at 30m. 

Figure 6 MMANA antenna model indicating uniform low angled radiation pattern at 20m. 

Figure 6 MMANA 3D antenna model indicating uniform low angled radiation pattern at 20m.

Figure 6 MMANA antenna model indicating uniform low angled radiation pattern at 17m. 

Figure 6 MMANA 3D antenna model indicating uniform low angled radiation pattern at 17m.

Figure 6 MMANA antenna model indicating uniform low angled radiation pattern at 15m. 

Figure 6 MMANA 3D antenna model indicating uniform low angled radiation pattern at 15m.

Figure 6 MMANA antenna model indicating uniform low angled radiation pattern at 12m.

Figure 6 MMANA 3D antenna model indicating uniform low angled radiation pattern at 12m.

Figure 6 MMANA antenna model still indicating uniform low angled radiation pattern, however higher angle bulge developing at 10m.

Figure 6 MMANA 3D antenna model still indicating uniform low angled radiation pattern, however higher angle bulge developing at 10m.

Operational notes

The antenna has been set up at several locations and has shown consistent performance, with predictable matching at each site. On the 40m band, the antenna demonstrated meaningful capability by reliably connecting to a Winlink gateway approximately 200 km away.

References  

American Radio Relay League. (1974). The ARRL Antenna Book. Newington, CT: ARRL.

Makoto Mori. (n.d.). MMANA-GAL antenna modelling software. Retrieved from https://hamsoft.ca/pages/mmana-gal.php

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Page initiated 03 September, 2025 

Page last revised 09 December, 2025