The higher the radio sensitivity, the better
Sensitivity is not as high as possible
Some people often boast that the higher the sensitivity, the better, but not always "the more sensitive, the better", for example, it is not suitable for listening to high-power radio stations of hundreds of kilowatts (KW), a 0.1uV (microvolt) The radio may not be easier to receive broadcasts than the 0.5uV model. International tests often indicate intelligible, for example: an experienced CW operator can interpret a CW signal that is only 1.4 times (2dB) higher than the background noise , But the voice signal is higher. Broadcasting a signal that is 4 times (12dB) higher than the background noise is also a little difficult. If it is increased to a difference of 10 times (20dB), it can be easily listened to, and the gap is increased to 20 times ( 26dB) to listen to the clear signal without any effort.
When listening to the radio, the receiving antenna not only senses the broadcast signal, but also receives a lot of background noise. These different forms of noise are divided into 3 types:
1. Cosmic noise (galacTIc noise): Among them, the sun is the largest source, and reception below 100MHz will be affected.
2. Atmosphere noise (atmosphere noise): Because there are nearly 30,000 thunderstorms every day, the lightning caused will increase the background noise, especially in the tropical region. The reception is more seriously affected, which is also the tropical frequency band (2.3- 6.3MHz) One of the reasons why it is not easy to receive.
3. Man-made noise: This is everything you use when you receive a letter, such as a washing machine, desk lamp, drilling machine, car start, even if you live in the suburbs, the power line passing through is a super Broadband noise transmitter.
The background noise caused by the interference of all electrical appliances is much higher than the atmospheric noise by 10 times. The intensity of the cosmic noise in the following data can be inferred how serious the man-made noise is.
Suppose you want to listen to a 7.2MHz (7200kHz) broadcast signal. When you reach the radio, the intensity is just 0.90uV. Obviously you ca n’t hear it unless the radio signal needs to be increased to 3.16 times (10dB) or more to overcome the cosmic noise. The receiver's factors are taken into account! The more sensitive radio only obtains a stronger signal index, but compared with the less sensitive radio, the difference between the two (signal / noise ratio) has not changed at all. !
Therefore, it is not helpful for the radio to amplify the signal with a broadband amplifier, but the signal index is higher, but it will make the reception worse. This has not added the factors of man-made noise, it is assumed that the internal circuit of the radio does not produce noise. Premise.
Based on the above description. We have a strong reason to suggest not to look for sensitive radios, but to look at other indicators such as selectivity (selecTIvity), cross-modulation (cross-modulaTIon), inter-modulation (inter-modulaTIon), etc. digital.
After reading this article, do you think a radio with a sensitivity of 0.1uV will be better than a radio with 0.5uV?
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