P.S.: On May 12, 2025 at 11:47 AM, the remote station for lactic acid bacteria successfully completed the first 144 MHz DX communication of the year 2025.
Most enthusiasts have some familiarity with UV DX, and typical communication ranges are around 100km. Achieving a connection over 200km is already quite impressive. If you suddenly manage to connect with a signal from that distance, it's likely due to DX (distant) communication. UHF long-distance communication within China is less common, while VHF long-distance communication is more prevalent. VHF includes the 2m and 6m bands. With 2m, you can typically communicate with most regions in China and Japan, while 6m allows for communication with nearby Asian countries, and occasionally even Europe. This raises a question:
How did dx 通联 come about, and what are its characteristics in terms of dissemination?
How do I know when to activate broadcasting and at what frequency should it be activated?
What equipment and antenna do I need to achieve long-distance DX communication?
1. The propagation paths and characteristics of DX communication, particularly in the 6m band, primarily rely on sporadic-E layer propagation and F-layer ionospheric propagation, as well as annual meteor reflection and aurora reflection communications.
1.1.1 The most common summer propagation mode is a sudden E-layer reflection. Most of China falls within the Northern Hemisphere, and this typically occurs between May and August. However, occasional occurrences can also happen in January and February. This propagation primarily takes place during the daytime, with a range of up to 2000 km per hop. We often experience successful communication with Australia and New Zealand during the early months of the year using this mode. During the summer months, we can also achieve continuous communication with Japan and within China throughout the day. In the transition period between summer and autumn, communication is possible with Europe south of the 4th region. Furthermore, this propagation mode exhibits strong bursts and QSB (signal fading) effects.
1.1.2 For F-layer reflection, as long as the year relies on the solar cycle (11-year period), specifically during peak periods, stable communication between domestic and Japan is possible.
1.1.3 Meteor Scatter: This occurs annually, but the success rate varies each year. In 2023, most people were successful in using meteor scatter (which relies on the ionization of the atmosphere caused by meteor friction). Meteor scatter has a short availability window (during meteor transit and for a period after), with very unstable signal conditions (the signal may disappear suddenly). We use the MSK144 mode for meteor scatter.（WSJT-X), 50.260 MHz(USB)。
1.4 Aurora reflection, primarily occurring in Russia and northern border regions of China, was observed with a large number of Russian radio stations communicating on the 6m band during its establishment.
1.2 For DX communication in the 2 MHz band, it primarily relies on sporadic E layer ionization, meteor debris scattering, aurora reflection, and equatorial disturbance propagation.
1.2.1 For DX communication in the 2 MHz band, sporadic E-layer propagation is an important method. The propagation period is typically from April to August (summer months), but the exact opening times are unpredictable and can vary significantly (ranging from a few minutes to several hours, or even disappearing within a minute). Sporadic E-layer propagation requires a radio station and ground system that can operate 24/7 to ensure continuous communication of sporadic signals. Once this type of propagation is established, it typically covers distances of over 1500 km, such as the recent connections with Japan and various regions within China.>! (A particularly interesting experience in 2024, when the 144MHz band was opened in Area 2, was that after comparing spot reports and maps, it became clear that there was a reflective surface above the Bohai Sea and Yellow Sea, which initially connected Areas 4/5 and Japan. Over time, this "cloud" moved north, gradually allowing Area 2 to connect with Japan, and the signal strength gradually increased.)
1.2.2 The scattering of meteor debris in the 2m wavelength band presents a significant challenge, requiring high antenna system and equipment power requirements.
1.2.3 Access to the Aurora launch is a privilege reserved for our Russian friends.
1.2.4 Equatorial disturbances also apply to Brazilian and Indian friends.
2. Regarding the timing and frequency of activation.
2.1 The propagation period is typically from April to August, coinciding with the transition between winter and spring. During this time, we can gradually start communicating with friends in Australia and New Zealand, and around May, we can establish stable communication with Japan. In late July and early August, we can also connect remotely to Southern European regions. The propagation period for 2m typically begins in April or May. We use FM DX (FM broadcast signals across cities) and stable communication at 50.31 MHz (a large number of stable Japanese radio stations) to assess the possibility of opening communication on 144 MHz. Domestic HAMs also monitor the situation, waiting for propagation to begin. Additionally, we can use observation software to monitor the propagation conditions.https://pskreporter.info/pskmap.html This website is a well-known reporting site for radio signals, allowing users to monitor and report on the status of transmissions in specific areas at specified frequencies and times.
2.2 6/2m Most domestic enthusiasts use the FT8 digital mode, so the frequency is 50.313 MHz.(USB)144.46 MHz（USB)If the communication channel can be stably established, it will be possible to communicate with other frequencies using SSB, CW, and FM.
3. To achieve DX communication, I need specific equipment and antennas. For the 6-meter band, once a reliable connection is established, standard Yagi antennas like the V750 and GP antennas, along with support for 50 MHz full-mode radios, can be used to communicate effectively. However, if you require communication with more stations, I recommend using the BG7XWF-designed shortwave Yagi antenna (with a main boom that is one wavelength – approximately 6 meters) for optimal performance. Southern friends can use this antenna to easily connect with European stations.
Regarding the 2m band, we need a radio that supports UV full mode. The following shows a list of UV radios that support full mode (excluding the uvk6, as the k6's SSB mode actually has a bandwidth equivalent to FM and pollutes the spectrum). For beginners, the Yaesu FT-897 or FT-817nd offer the best value.
For the 2-meter band, most good Southern propagation results use Yagi antennas. Some also use GP antennas. In May 2023, I achieved my first remote communication on 144 MHz. At that time, I didn't have the conditions to install a rooftop Yagi antenna (on the 34th floor of a 16-story building), so I installed a 5-element Yagi antenna made by JYR indoors. The equipment was an IC-9700 with 25W power. The signal strength was very strong when the communication was first established. The first 2-meter connection occurred in the afternoon, and I only realized that there were many signals from Southern China and Japan after waking up.
A VHF Yagi antenna installed indoors provides good results, and many domestic enthusiasts have also achieved DX on the 144 frequency using this mounting method (the image shows a BH6KWC antenna).
After the 144MHz transmission was opened, power wasn't a critical factor. During the summer of 2024, I forgot to adjust the power before leaving home, and only realized that the actual transmitting power was 1% (less than 1W) when I tried to connect. However, I successfully connected with many Japanese and Taiwanese radio stations. Please remember to comply with all applicable laws and regulations when connecting.
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