The environmental pollution caused by the three wastes of life and industry (waste water, exhaust gas, waste residue) is known to all ****. In addition to this, there is light pollution (city lights at night in big cities, neon lights), damage to the human optic nerve, affecting the astronomical optical observation.
Electromagnetic pollution, affecting human survival, causing mechanical and electrical equipment malfunction, affecting radio communications, but also affect our radio enthusiasts radio reception.
The causes of electromagnetic pollution:
1 household appliances: microwave ovens, electronic dimming lighting, equipment, such as switching power supply stray radiation, mainly due to the product of electromagnetic compatibility (radiation) test failed, and the market caused by.
2 industrial equipment: high-frequency (microwave) processing equipment, medical nuclear magnetic **** vibration of medical equipment, such as improper shielding measures.
3 communications equipment: communications transmitters (mainly paging station transmitters, 60% of the transmitter) of the residual sideband (out-of-band) radiation, multiple transmitting equipment, the secondary intermodulation (mainly odd intermodulation) radiation, the transmitter circuit filtering is not good.
4 man-made reasons: electromagnetic confrontation on the battlefield electronic warfare (such as the Gulf War), near-earth high-altitude detonation of nuclear bombs (wacky netizen's tricks), resulting in the paralysis of the enemy's communications equipment.
5 Natural disasters: solar flare outbreaks (high-energy particles disrupt the ionosphere), short-wave communication disruption.
6 Other factors.
The current situation of electromagnetic pollution (limited to the Shenzhen area, other areas can be referred to):
Measured by the spectrometer, the HF section of the background noise level is generally in the -80DB or so, the source of contamination is mainly the power grid power supply lines and power equipment 50HZ, 100HZ radiation, leaving about 30 meters, basically undetectable.
30MHZ - 130MHZ section of the background noise level in -80DB or so, basically no interference.
137MHZ-175MHZ section background noise level in -60DB, individual sections in -35DB, especially in the paging antenna concentrated section (about 300 meters radius), the formation of electronic smoke area (electronic barrier), the outside world is difficult to penetrate radio signals, GSM 900MHZ signal is also affected. The 900MHZ signal of GSM is also affected, and the spectrum analyzer is noisy.
400MHZ - 470MHZ section of the background noise - 75DB, U section of the car and paging station link transmitter spurious radiation is mainly.
500MHZ - 1000MHZ section of the background noise in -85DB or so, basically no interference.
Small Wutong Mountain (Shenzhen's high mountains, 625 meters above sea level), background noise -45DB, 500KHZ-1000MHZ are interference, GSM and analog cell phones (big brother), basically can not call in and out.
Di Wang Building (Shenzhen's tallest building, 320 meters high) and Wutong Mountain, the same, the whole section of interference.
Yinhu Peak (not Penjianshan), about 100 meters high, noise level -90DB, basically no interference.
Near Meilin Reservoir (including Meilin 1 Village), background noise -80DB.