The classification and application method of Hengaode analytical field strength meter The field strength meter, as the name suggests, is an instrument for measuring field strength. The value of the field strength meter is μV / m, and it has a length unit m. In principle, the voltage value measured by the level meter (or voltmeter) is at the input port of the meter, and the voltage (or potential) measured by the field strength meter is the voltage induced by the antenna at a certain point in the air. Strictly speaking, the field strength meter is composed of a level meter and an antenna. distinguish As we all know, the level meter is in units of decibel (dB), such as dBμV, dBmV, dBm, and the voltmeter is in units of volts (V), such as V, mV, μV, KV, etc. In fact, the level and voltage are the same physical quantity. Therefore, in many cases, these two units are marked at the same time in an instrument. In a sense, the voltmeter is also a level meter, and the level meter is also a level voltage. The watch is just used to call it separately. In terms of field strength on the market, they also separate the technical indicators of the level meter from the antenna. For example, Japan Anritsu ’s ML524 field strength meter host provides technical indicators according to a level meter, frequency range, sensitivity, level measurement range, level test accuracy, and antennas MP534A, MP666A as options, technical indicators are given by frequency band And antenna coefficients. At present, the PTK3201 field strength meter commonly used in the domestic wireless field is produced according to the level meter. The frequency range is 0.1 ~ 2000MHz, and the sensitivity is 0.3mV. It is given by the instrument input port. There is a whip antenna, no The antenna coefficient can only measure the signal field strength qualitatively. If you want to determine the field strength in dBμV / m, you need to choose a measurement antenna. This shows that the level and field strength, level meter and field strength meter are very different. However, it is often confused in some occasions, especially in the scope of China's cable TV industry. The cable TV signal is measured by measuring the level of the sync head in dBμV. It should be called a TV signal level meter, or level meter. However, starting with the use of public antennas in China, somehow they are called field strength meters. The earliest cable field strength meter in the world is LFC944 produced by Japan's Lida company. Lida's original text is a TV signal level meter. Since then, many people have called it a field strength meter. I have been in the CATV industry many times. It was suggested that it should be called a level meter, perhaps because there are too many people called it, and it is still called a field strength meter. Even foreigners have to recognize this name when they communicate in China. That is only wrong by mistake. Regarding the "misnamed" field strength meter in the scope of cable TV, the author has classified it as a TV field strength meter, a TV spectrum image field strength meter, a CATV analyzer, and a spectrum analyzer, which have been recognized by peers and experts. Narrate. Features Field strength meter As far as the field strength meter is concerned, it is very closely related to the antenna. If a certain measurement accuracy is required, then from equation (1), it is directly related to the antenna gain Ga, and then to the antenna's operating frequency range, which is At the very least, it cannot be said that it is enough to just find an antenna and connect it to the level meter. Therefore, in practice, this kind of antenna is called a test antenna, and it has strict technical specifications, such as frequency range, antenna gain and impedance, standing wave ratio, front-to-back ratio, and so on. In order to adapt to its frequency range, its shape is very different, there are whip antenna, half-wave dipole antenna, log period antenna, loop antenna, etc. The test antenna with high requirements is also quite expensive. For example, the test antenna of Anritsu in Japan is about 1/4 of the main unit. In the past, the field strength meter always supplied the antenna. That is to say, a field strength meter must be the host (level meter) equipped with the antenna. With the development of electronic technology and electronic measurement technology, especially since the 1980s, a large number of spectrum analyzers have been used, there are fewer and fewer single field strength meters, and even a single level meter is also less and less (Unless highly professional use), because its function can be replaced by a spectrum analyzer agent. In principle, the basic principle blocks of the spectrum analyzer, level meter, and field strength meter (host) are the same. The spectrum analyzer itself measures the signal level within the spectrum range. If "zero transconductance" is used, it is a frequency selection level meter. If the standard test antenna is added to the spectrum analyzer, is it not the measurable field strength? A better spectrum analyzer can store the antenna coefficient in the machine and directly display the field strength value μV / m when used. For example, Agilent and Anritsu spectrum analyzers have antenna coefficient storage function. As far as Anritsu in Japan is concerned, the field strength meters ML518, HM650, MH649 produced in the 1980s have a relatively large sales volume, and China has also bought a lot of them. At the same time, spectrum analyzers MS610, MS2601, etc. were produced, and the field strength meter and spectrum analyzer can use the same antennas MP534, MP651, MP663, etc. to measure the field strength. They have similar indicators and similar prices. Of course, users choose powerful spectrum analyzers. My domestic field strength meter is also rarely produced. The main reason is also due to the replacement of the spectrum meter. Instructions ①Connect the cable correctly, and the connecting cable should not be too long. If it is not necessary to use a long cable, the loss of the cable must be added to the reading of the instrument, especially in the high frequency band. ②The field strength meter should not only measure the image carrier level, but also the carrier level of the FM sound broadcasting signal. Therefore, the signal level used should include the sound carrier level and the image carrier level. The sound carrier level is defined as the effective value of the unmodulated sound carrier voltage at the 75 Ω terminal, expressed in dBμV. The image carrier level is defined as the effective value of the image carrier voltage at the modulation envelope peak (synchronization header) on the 75 Ω terminal, expressed in dBμV. Therefore, the measurement detector of the image carrier level should be a peak detector, and care should be taken when using it. ③ Use the ambient temperature. In winter in the north, attention should be paid to heat preservation measures. In the south of midsummer, try to avoid placing the instrument directly under the sun, otherwise the reading error will greatly exceed the range of technical indicators. ④The field strength meter should be moved frequently, and be careful not to collide, so as not to damage the shell of the instrument and the accuracy of descent. ⑤ The field strength meter must be periodically measured or compared with the field strength meter that has been specially measured to avoid inaccurate judgment of the instrument
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