HF Low Band DX propagation status
Generally, above 10MHz is suitable for intercommunication between half of the earth in a thousand kilometers away or in the sunshine area, while below 10MHz is very suitable for intercommunication within 24 hours within 1000 kilometers or between half of the earth in the dark area, so there are two main periods of communication with Europe :
1. Locally use the frequency above 10MHz from 2 noon (European sunrise) to midnight (European noon) in the evening.
2. Local intercommunication between 2:00 midnight (European sunset) and 7:00 am before using the band below 10MHz.
Generally, the ionospheric reflection is within a distance of about 3000 kilometers, the path loss is about 100 ～ 120db (1010 ～ 1012 power ratio 105 ～ 106 voltage ratio), and then the power drops about 3 ～ 6db (100.3 ～ 100.6 or 2 ～ 4) Times), the farthest call in the earth is about 20,000 kilometers, and it is estimated that 100 ～ 120db plus 6db × 7 (20000km / 3000km = 7 times) = 100 ～ 120 + 42db (21db) = 121 ～ 141 → 142 ～ 168 The power required for 20,000 kilometers in South America is about 20mW ~ 2W → 200W, it is possible to reach. The probability of high power is high, and the low power may be less than a few throughout the year. The general frequency is high and the power is low. In the summer, 2W power can be connected to the Netherlands and Germany with 29MHz FM. In the morning, it can be connected to the United States and California. (In the evening, 2W power can be used to connect South America and Brazil to 7MHz); then 50W to Japan, Taiwan 14MHz, 28MHz USB And 29MHz FM, 50MHz SSB is not difficult, but the time limit is not available throughout the year.
For intercommunication within 500 kilometers, the frequency band below 10MHz reflected by the ionosphere should be used. The following practical frequencies have been confirmed for decades: Fuzhou, Fujian broadcast to Taiwan 2340KHz, 3900KHz, 4900KHz, 5040KHz, Shanghai Pujiang Voice Pair Taiwan 3280KHz, 5075KHz, (4950KHz, 7280KHz), Taipei International Voice built in the central 6040, 6085, 6180, 7105, 7130, 7280, 7445, 6300, 9280, 9610, 9630, 9690KHz, all-day Taiwan Fisheries Station 4649.5KHz USB, domestic NSB (Shortwave Broadcasting in Japan) 3925, 6055, 9595KHz, North Korea to South Korea pointer station 2850KHz, South Korea 5975KHz, and East Asia Airway Meteorological Station 2863, 6679, 8828, 13282KHz are radio propagation characteristics for more than 20 years Check the beacon station. Broadcasted 24 hours in Darwin, Northern Australia. The three stations use a high frequency in the daytime at a distance of about 500 kilometers. At night, they fear that they will not be able to reflect in the near distance in winter to reduce the frequency. KATHERINE 5025 daytime, 2485KHz nighttime, TENNANT Greek 4910KHz daytime, 2325KHz nighttime, ALICE springs 4835KHz during the day and 2310KHz at night, the frequency generally decreases near the poles at high latitudes.
From September to Darwin, the signal below 12MHz in Taiwan ’s radio stations will gradually increase after 4pm every day. The signal at 6040 is strong after sunset, and the small radio is clear without antennas. After 9pm, the 738KHz / 1143KHz and 548KHz signals from Zhongbo Fisheries It is clear and good that it subsides at 5 o'clock in the morning, and there is no signal until 15 MHz after 9 o'clock in the morning. It is almost not easy for DX to be below 15 MHz at noon. The E / Es layer reflects radio waves within 2,000 kilometers. It is not easy to reach 300 kilometers. Remote reflection intercom.
The frequency of rescue and listening in Japan is 4630KHz CW.
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