AM radio

The circuit of Fig. 4 can also be used as a detector of amplitude-modulated (AM) radio waves. Fig. 5(a) illustrates the components of an AM wave. If this is applied to the input of Fig. 4, the wave is rectified and the output appears as shown in Fig. 5(b). Placing a small-valued capacitor across Rl filters out the carrier frequency and the desired modulating signal is obtained, as shown in Fig. 5(c). 

Although there is no interference from other NQR signals, other types of signals may interfere with NQR explosives detection. For unshielded detector coils, the primary culprit is RF interference (RFI). Most NQR frequencies of interest for explosives detection fall in the frequency range of 0.5-5 MHz. The biggest problem in this range is the amplitude modulation (AM) radio band, from 0.5 to 1.5 MHz. Besides radio transmissions, other sources of RFI can include nearby electrical equipment, power transmission lines and lightning strikes. 

Compare the energy (in joules) carried by an x-ray photon (wavelength A = 0.20 nm) with that carried by an AM radio wave photon (A = 200 m). Calculate the energy of 1.00 mol of each type of photon. What effect do you expect each type of radiation to have for inducing chemical reactions in the substances through which it passes ... 

Nonionizing radiation consists of parts of the electromagnetic spectrum that correspond to microwaves, also identified as RF waves and extremely low frequency (ELF) waves. RF waves range from 300 MHz to 30 GHz and correspond to AM radio, FM radio, TV, mobile telephone, and micro-wave oven transmissions. ELF waves are in the 50-60 Hz range and correspond to electrical transmission power line emissions. 

Two different schemes are used for modulation chopper stabilization, which works similarly to an AM radio, and correlated double sampling (CDS), which performs two measurements of the noise only and the noise plus signal [19]. Fig. 6.1.11 shows conceptual diagrams of the two techniques. Although the additional circuitry looks complex, actual implementations are surprisingly simple [20, 21]. 

A high frequency radio beacon with a minimum range of 30 miles can be provided for the guidance of approaching helicopters, and VHP/AM radio would be provided for communication with pilots to comply with the appropriate standards, for the location. 

Frequenqf is expressed in cycles per second, a unit also called a hertz (Hz). Because it is understood that cycles are involved, the units of frequency are normally given simply as per second, which is denoted by s or /s. For example, a frequency of 820 kilohertz (kHz), a typical frequency for an AM radio station, could be written as... 

An AM radio station broadcasts at 1010 kHz, and its FM partner broadcasts at 98.3 MHz. Calculate and compare the energy of the photons emitted by these two radio stations. 

The signal from a resonant transducer resembles an AM radio signal. It has a carrier wave, at the resonance frequency of the transducer, which is amplitude modulated by the process. The information about the process is in the modulation envelope. An RMS-to-DC (root mean square-to-direct current) converter is used to demodulate the signal. The output of this device is the amplitude of the envelope. 

Amplitude Modulation (AM). With AM radio, the amphtude (height) of the transmitted signal is made proportional to the sound amplitude captured (transduced) by the microphone. The transmitted frequency remains constant. AM transmission is degraded by static and interference because sources of electromagnetic transmission such as lightning and automobile ignitions, which are at the same frequency, add their amplitudes to that of the transmitted signal. AM radio stations in the United States and Canada are limited to 50 kilowatts (kW). Early twentieth century, U.S. stations had powers up to 500 kW, some of which could be heard worldwide. 

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