Dr. FB

Even if there are days when we can't hear DX on CW or SSB, we can hear the FT8 sounds for DX stations every day. It's amazing, and is a wonderful mode! FT8 is widely used not only in the HF band but also in VHF and UHF, but even if I provide the topic of the super-high frequency band of 2400 MHz, it may not be useful for daily amateur radio activities and it may be meaningless because most of hams do not have such super-high frequency radios. Even so, with the trend of 5G (5th Generation) in the world, I dismantled the 802.11b/g compatible (2.4 GHz band) wireless LAN antenna, thinking that the era of millimeter waves would come to amateur radio.

2.4 GHz band of wireless LAN and 2400 MHz band of amateur radio

Wi-Fi peripherals are assigned two frequency bands, 2.4 GHz and 5 GHz. In addition to communication with a relatively short distance such as the connection between a cellular-phone and peripheral devices in the 2.4 GHz band, it is possible to perform communications between two points that are quite far apart by connecting an external antenna. Data communications between two points using this 2.4 GHz band is performed in areas and places where wired LAN connection is not possible. This is also called inter-building communications, and this is where we amateur radio operators are interested in. Figure 1 shows the 2.4 GHz band antenna used for the inter-building communications.

Figure 1. Installation example of wireless LAN antenna for 2.4 GHz (802.11b/g)

13 channels are allocated for the 2.4 GHz band wireless LAN in Japan. Allocated frequencies are between 2.412 GHz (2412 MHz) as channel 1 and 2.472 GHz (2472 MHz) as channel 13 in 0.005 GHz (5 MHz) increments. On the other hand, the frequency of the 2400 MHz band assigned to amateur radio is 2400 to 2450 MHz, so there is a part that overlaps with the frequency of wireless LAN and I think we can use the Wi-Fi antenna in the amateur 2400 MHz band.

The wavelength of the 2400 MHz band is as short as 12.5 cm, and although advanced technology is required for building such super-high frequency antenna, it can be said that it is a reasonable size for making your own antenna. The 2400 MHz band radio is also used only by some enthusiasts, and even if I provide the topic of antennas here, I cannot measure or experiment, but as a technology to enjoy watching, I dismantle the antenna in Figure 1. The contents are shown in Figures 2 and 3.

Antenna dismantling

The antenna I got is an antenna for outdoor installation for the wireless LAN (Wi-Fi) using the 2.4 GHz band. Figure 2 shows the appearance of the antenna. As you can see in the photos, it is covered with plastic case and it is designed as weather-proof.

Figure 2. The antenna is covered with plastic case.

Figure 3 shows a photo of the inside with the antenna cover removed. It was a Yagi antenna as I had imagined. The composition is an 8-element Yagi beam antenna, and the radiator part is formed a folded dipole probably because it takes a broadband. The wavelength of 2400 MHz is calculated to be 0.125 m (= 12.5 cm), and the left and right length of the radiator is λ/2, so it should be 6.25 cm (= 62.5 mm). The actual measurement is 53 mm, which is nearly 10 mm shorter than the calculation.

Figure 3. Inside view of the antenna

The matching section is designed as hairpin matching that is often seen in HF band multi-band and multi-element Yagi antennas. Figure 3 shows the length or size of the matching part and other elements. Figure 4 shows an enlarged photo of the matching section.

Figure 4. Structure of hairpin matching section

Antenna radiation pattern

Figure 5 shows a characteristic diagram of an antenna equivalent to the disassembled antenna.

Figure 5. Radiation patterns of disassembled antenna (quoted from Icom website)

FBDX

<Reference>
In the part that explains the frequency of wireless LAN in the text, it is expressed as "GHz" according to the explanation of IEEE 802.11b/g, and in the part that explains the frequency band of amateur radio, it is expressed as "MHz" according to the US frequency allocation. The standard name of IEEE is omitted in the text as an abbreviation.