6-way antenna switch using a common rotary switch

Created: Sep. 2025

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Introduction

To compare different aerials, we previously used a simple toggle switch but the SPDT configuration limits the comparison to two aerials only [1]. This project arises from a need to compare more than 2 aerials.

Material & method

This project is based on a DP6T rotary switch but, uses 1 pole only (fig. 1-2). The switch's 6 "Throws" terminals are arranged in a semi-circle around the Common "pole" (fig. 2). These terminals are connected to BNC females using RG-174 coax cables.

Fig. 1: Circuit of 6-way aerial switch (top) and the COMMON cable's braid arrangement (bottom)

Fig. 2: The switch's 6 "Throws" terminals are arranged in a semi-circle around the Common "pole" (top). These terminals are connected to their respective BNC females using RG-174 coax cables (bottom)

Experiments revealed that the switch's matching / Return Loss (RL) can be improved by two things:

1. Minimize unshielded ends of coax cable connections to BNC and switch. In practice, the coax jackets were stripped ~7 mm from the ends.

2. At switch end, connect all coax braids / shields directly to COM shield using STAR connection (fig. 3). To enable the STAR connection, the COM braid has to be divided into 6 parts (fig. 1, bottom). When the braids are STAR connected, the 100 MHz Return Loss (RL) is 17 dB versus the Daisy connected's 13 dB. We speculate that the STAR connection improves matching by minimizing the length between braids.

Fig. 3: Compared to Daisy connection of the braids (top), STAR connection (bottom) can improve the Return Loss.

The switch is built into a recycled die-cast casing measuring 15 x 7.5 x4 cm (fig. 4).

Fig. 4: The switch is built into a recycled die-cast box measuring 15 x 7.5 x4 cm

For competitor analysis, a commercial product containing the same rotary switch is used for comparison (fig. 5). This product is marketed as MJ or Opex CX-3 [2]. Measurements of this product was performed by an independent party [3].

Fig. 5: A commercial product, MJ or Opex CX-3, is used for competitor analysis

Results

The prototype achieves good impedance match and insertion loss over HF and low VHF. The RL is better than 27 dB (SWR <1.1) up to 30 MHz (fig. 6). Extending upward to 100 MHz, RL is better than 17 dB (SWR <1.4). Insertion loss is <0.1 dB and <0.2 dB to 30 MHz and 100 MHz, respectively.

Fig. 6: The prototype achieves good impedance match and insertion loss over HF and low VHF. The RL is >27 dB (SWR <1.1) and >17 dB (SWR <1.4) up to 30 MHz & 100 MHz, respectively. Insertion loss is <0.1 dB and <0.2 dB to 30 MHz and 100 MHz, respectively.

The prototype exhibits good isolation (ISO) over HF and low VHF. The ISO is better than 47 dB and 37 dB to 30 MHz and 100 MHz, respectively (fig. 7).

Fig. 7: Isolation (ISO) is good over HF and low VHF; i.e. >47 dB and >37 dB to 30 MHz and 100 MHz, respectively

The prototype can outperforming commercial products; i.e. the former has superior loss and isolation performances compared to the MJ / Opek CX-3R switch (fig. 8). We were unable to compare RL / SWR because the latter lacked trustworthy measurement.

Fig. 8: Performance table showing the prototype outperforms the compared commercial switch MJ / Opex CX-3R

Conclusion

A 6-way antenna switch for HF has been built using a common rotary DP6T switch. The prototype outperforms a commercially available antenna switch.

To further extend the frequency range is desired, a possible solution is to shorten the switch terminals to minimize parasitic inductance. Another solution is to mount the switch on a microstrip PCB in order to eliminate the parasitics at the coax ends.

References

[1] 9M2LCL, "DC-1GHz switch from a common toggle switch", https://sites.google.com/site/randomwok/Home/electronic-projects/test-equipment-accessories/dc-1ghz-switch-with-a-common-toggle-switch

[2] Autotek Limited, “CX-3”. https://www.opekantenna.com/CX-3.htm

[3] KP4MD, “CX-3 Coaxial Antenna Switch”, Aug. 2016. https://photos.google.com/share/AF1QipPMoi52i38Q-a2T-TQuvT7T32403F5q1uTrj-7pDuzJP6CyYzzasJiueNpTFCXr2g?

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