The phrase “PC load letter” is a printer error message on some mostly obsolete types of HP laserjet printers. Here, “PC” stands for “paper cassette” and the error indicates that no letter-sized paper is available for a print job with a letter size. The error message is instructing the user to load a letter-sized paper into the printer.
Radio frequency monitoring (RFM) is a wireless communication technology that consists of at least two components, each capable of detecting the presence or absence of the other. Depending on the application, one component may record the date and time the other component fails to receive a monitoring radio frequency (RF) signal. When the monitoring signal is again received, matching data is again recorded. RFM uses the same technology as radio frequency identification or RFID.
Radio frequency oscillation is between 30 KHz (kilo hertz or 1000 cycles per second) and 300 GHz (Giga hertz or 1.0 billion cycles per second). Alternating current (AC), unlike direct current (DC), possesses a special property by radiating electromagnetic waves from a conductor; this is the basis of RF technology. Different frequencies propagate through different medium for varying distances; for example, some high frequency (HF; 3 to 30 MHz) and very high frequency (VHF; 30 MHz to 300 MHz) systems may transmit signals of more than 90 feet.
One of the most common uses of radio frequency monitoring is a technology used by city and county law enforcement agencies. They monitor the presence or absence of defendants who are subject to house arrest. The equipment includes both an ankle bracelet and a monitoring base station.
Examples of other industries using this technology include:
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