Title: Seismometer
Content: of such strength, these tools have only been getting stronger in recent years. The modern broadband seismograph can record a very broad range of frequencies. It consists of a small "proof mass", confined by electrical forces, driven by sophisticated electronics. As the earth moves, the electronics attempt to hold the mass steady through a feedback circuit. The amount of force necessary to achieve this is then recorded. In most designs the electronics holds a mass motionless relative to the frame. This device is called a "force balance accelerometer". It measures acceleration instead of velocity of ground movement. Basically, the distance

Title: Magnetic detector
Content: standpoint, several subtle prerequisites are necessary for operation. The strength of the magnetic field of the permanent magnets at the iron band must be of the same order of magnitude as the strength of the field generated by the radio frequency excitation coil, allowing the radio frequency signal to exceed the threshold hysteresis (coercivity) of the iron. Also, the impedance of the tuner that supplies the radio signal must be low to match the low impedance of the excitation coil, requiring special tuner design considerations. The impedance of the telephone earphone must roughly match the impedance of the audio pickup

Title: Vacuum tube
Content: analog scopes (dependent upon CRTs) continue to be produced, are economical, and preferred by many technicians. At one time many radios used "magic eye tubes", a specialized sort of CRT used in place of a meter movement to indicate signal strength, or input level in a tape recorder. A modern indicator device, the vacuum fluorescent display (VFD) is also a sort of cathode ray tube. The X-ray tube is a type of cathode ray tube that generates X-rays when high voltage electrons hit the anode. Gyrotrons or vacuum masers, used to generate high-power millimeter band waves, are magnetic vacuum tubes

Title: Through-the-earth mine communications
Content: a spirit level, and driven at a few kHz. Though such a small antenna is a very poor radiator of propagating radio waves at this low frequency, its local AC magnetic field is strong enough to be detected by a similar receiving antenna up to a few hundred meters away. The received signal's strength and its dependence on orientation of the receiving coil yields approximate distance and directional information. There are several systems that have been recently developed. One system is known as the PED System, where PED is an acronym for personal emergency device. Initially developed after a mining

Title: Audion
Content: grid-iron (hence "grid"). The Audion provided power gain; with other detectors, all of the power to operate the headphones had to come from the antenna circuit itself. Consequently, weak transmitters could be heard at greater distances. De Forest and everybody else at the time greatly underestimated the potential of his original device, imagining it to be limited to mostly military applications. It is significant that he apparently never saw its potential as a telephone repeater amplifier, even though crude electromechanical "note magnifiers" had been the bane of the telephone industry for at least two decades. (Ironically, in the years of

Question: Which electronic device magnifies the strength of a signal?
Answer: Amplifier