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Noise Reduction Rating (NRR) is a measure of the effectiveness of a hearing protection device to reduce noise levels. Higher values indicate greater noise reduction. NRR values range up to approximately 30 dB. … NRR rating is based on a laboratory test where the hearing protection device is properly fit.
In electronics and telecommunications, modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a separate signal called the modulation signal that typically contains information to be transmitted. For example, the modulation signal might be an audio signal representing sound from a microphone, The carrier is higher in frequency than the modulation signal. The purpose of modulation is to impress the information on the carrier wave, which is used to carry the information to another location. In radio communication the modulated carrier is transmitted through space as a radio wave to a radio receiver.
In electromagnetics, an antenna’s power gain or simply gain is a key performance number which combines the antenna‘s directivity and electrical efficiency. In a transmitting antenna, the gain describes how well the antenna converts input power into radio waves headed in a specified direction. In a receiving antenna, the gain describes how well the antenna converts radio waves arriving from a specified direction into electrical power. When no direction is specified, gain is understood to refer to the peak value of the gain, the gain in the direction of the antenna’s main lobe. A plot of the gain as a function of direction is called the gain pattern or radiation pattern.
A battery’s capacity is the amount of electric charge it can deliver at the rated voltage. The more electrode material contained in the cell the greater its capacity. A small cell has less capacity than a larger cell with the same chemistry, although they develop the same open-circuit voltage. Capacity is measured in units such as amp-hour (A·h). The rated capacity of a battery is usually expressed as the product of 20 hours multiplied by the current that a new battery can consistently supply for 20 hours at 68 °F (20 °C), while remaining above a specified terminal voltage per cell. For example, a battery rated at 100 A·h can deliver 5 A over a 20-hour period at room temperature. The fraction of the stored charge that a battery can deliver depends on multiple factors, including battery chemistry, the rate at which the charge is delivered (current), the required terminal voltage, the storage period, ambient temperature and other factors.
Coaxial cable, or coax is a type of electrical cable consisting of an inner conductor surrounded by a concentric conducting shield, with the two separated by a dielectric (insulating material); many coaxial cables also have a protective outer sheath or jacket. The term “coaxial” refers to the inner conductor and the outer shield sharing a geometric axis.
Coaxial cable is a type of transmission line, used to carry high-frequency electrical signals with low losses. It is used in such applications as connecting radio transmitters and receivers to their antennas. It differs from other shielded cables because the dimensions of the cable and connectors are controlled to give a precise, constant conductor spacing, which is needed for it to function efficiently as a transmission line.
In a MOTOTRBO radio or repeater, there is a color code field which allows the selection of one of 15 colour codes. A radio which has been programmed with colour code 1 will not be able to transmit on a repeater configured with colour code 2 and so forth. A radio can be configured with multiple colour codes – one for each channel. A repeater can only be configured with one colour code.
Colour code is useful because it can prevent radios from one site or system mistakenly roaming to another site or system which uses the same frequencies. Although there is activity from the neighboring system, the radio will ignore all transmissions from the other system because it has a different colour code.
This is also useful for telecommunication regulators who have to allocate the same frequency to two DMR licencees in the same region. The regulator simply has to specify a colour code in the licence conditions – much like PL/DPL was used in analogue as a guard tone.
There is a limitation of course, if two geographically adjacent radio systems use the same frequencies, yet use a different colour code, there will be audio quality issues in the area where radio users are able to receive signals from both systems at roughly the same signal strength.
More recent systems use digital modulation, which impresses a digital signal consisting of a sequence of binary digits (bits), a bitstream, on the carrier. In frequency shift keying (FSK) modulation, used in computer buses and telemetry, the carrier signal is periodically shifted between two frequencies that represent the two binary digits. In digital baseband modulation (line coding) used to transmit data in serial computer bus cables and wired LAN computer networks such as Ethernet, the voltage on the line is switched between two amplitudes (voltage levels) representing the two binary digits, 0 and 1, and the carrier (clock) frequency is combined with the data. A more complicated digital modulation method that employs multiple carriers, orthogonal frequency division multiplexing (OFDM), is used in WiFi networks, digital radio stations and digital cable television transmission.
A duplexer is an electronic device that allows bi-directional (duplex) communication over a single path. In radar and radio communications systems, it isolates the receiver from the transmitter while permitting them to share a common antenna. Most radio repeater systems include a duplexer. Duplexers can be based on frequency (often a waveguide filter), polarization (such as an orthomode transducer), or timing (as is typical in radar).
Frequency is the number of occurrences of a repeating event per unit of time. It is also referred to as temporal frequency, which emphasizes the contrast to spatial frequency and angular frequency. Frequency is measured in hertz (Hz) which is equal to one occurrence of a repeating event per second. The period is the duration of time of one cycle in a repeating event, so the period is the reciprocal of the frequency. For example: if a newborn baby’s heart beats at a frequency of 120 times a minute (2 hertz), its period, T, — the time interval between beats—is half a second (60 seconds divided by 120 beats). Frequency is an important parameter used in science and engineering to specify the rate of oscillatory and vibratory phenomena, such as mechanical vibrations, audio signals (sound), radio waves, and light.
Frequency-division multiple access (FDMA) is a channel access method used in some multiple-access protocols. FDMA allows multiple users to send data through a single communication channel, such as a coaxial cable or microwave beam, by dividing the bandwidth of the channel into separate non-overlapping frequency sub-channels and allocating each sub-channel to a separate user. Users can send data through a subchannel by modulating it on a carrier wave at the subchannel’s frequency. It is used in satellite communication systems and telephone trunklines.
Frequency-division multiple access (FDMA) is a channel access method used in some multiple-access protocols. FDMA allows multiple users to send data through a single communication channel, such as a coaxial cable or microwave beam, by dividing the bandwidth of the channel into separate non-overlapping frequency sub-channels and allocating each sub-channel to a separate user. Users can send data through a subchannel by modulating it on a carrier wave at the subchannel’s frequency. It is used in satellite communication systems and telephone trunklines.
Motorola Type II refers to the second generation Motorola trunked radio systems that replaced fleets and subfleets with the concept of talkgroups and individual radio IDs. There are no dependencies on fleetmaps, therefore there are no limitations on how many radio IDs can participate on a talkgroup. This allows for greater flexibility for the agency. When scanning Motorola IDs, each Type II user ID appears as an even 4- or 5-digit number without a dash (example 2160).[1]
With the introduction of Type II, the “System ID” was also introduced. This is a four digit identifier unique to each trunking system. The purpose of the System ID is to allow radios to operate only on that specific system, and to identify each system. The System ID also allows for enhanced security because a radio now requires a System Key, unique to the System ID in order to be programmed onto any given system. Type I systems do not use unique System IDs, thus the possibility exists for overlapping coverage in busy areas.
The term SmartNet refers to a set of features that make Motorola Type I and II trunked systems APCO-16 compliant. These include better security, emergency signaling, dynamic regrouping, remote radio monitoring, and other features.
a Helmet kit is an assembly of a noise cancelling Dynamic MICROPHONE , Male connector to mate with an Incar Wiring Harness and drivers erpiece connector to be mounted on the helmet. Driver can choose between straight cord or coil cord.
Recent regulations in a few road racing series in North America prohibits drilling a helmet to install the HELMET KIT, for safety purposes.
The 2 most popular connectors for helmet kits are ” IMSA ” thye and ” NASCAR ” Type.
in the early days the switchcraft 297 3 contacts connector was used by numerous NASCAR drivers in US
NEXUS TP120 4 contacts connector was adopted in road racing and is known as ” IMSA ” type
The new trend is to go IMSA in all series.
A sales person or radio repair shop would understand the word mobile to mean vehicle-mounted: a transmitter-receiver (transceiver) used for radio communications from a vehicle. Mobile radios are mounted to a motor vehicle usually with the microphone and control panel in reach of the driver. In the US, such a device is typically powered by the host vehicle’s 12 Volt electrical system.
Push-to-talk (PTT), also known as press-to-transmit, is a method of having conversations or talking on half-duplex communication lines, including two-way radio, using a momentary button to switch from voice reception mode to transmit mode.
in telecommunications, Continuous Tone-Coded Squelch System or CTCSS is one type of circuit that is used to reduce the annoyance of listening to other users on a shared two-way radio communications channel. (See squelch.) It is sometimes referred to as tone squelch. It does this by adding a low frequency audio tone to the voice. Where more than one group of users is on the same radio frequency (called co-channel users), CTCSS circuitry mutes those users who are using a different CTCSS tone or no CTCSS. It is sometimes referred to as a sub-channel, but this is a misnomer because no additional channels are created. All users with different CTCSS tones on the same channel are still transmitting on the identical radio frequency, and their transmissions interfere with each other; however; the interference is masked under most (but not all) conditions. The CTCSS feature also does not offer any security.
A receiver with just a carrier or noise squelch does not suppress any sufficiently strong signal; in CTCSS mode it unmutes only when the signal also carries the correct sub-audible audio tone. The tones are not actually below the range of human hearing, but are poorly reproduced by most communications-grade speakers and in any event are usually filtered out before being sent to the speaker or headphone. CTCSS can be regarded as a form of in-band signaling.
A radio frequency power amplifier (RF power amplifier) is a type of electronic amplifier that converts a low-power radio-frequency signal into a higher power signal. Typically, RF power amplifiers drive the antenna of a transmitter. Design goals often include gain, power output, bandwidth, power efficiency, linearity (low signal compression at rated output), input and output impedance matching, and heat dissipation.
in telecommunications, a repeater is an electronic device that receives a signal and retransmits it. Repeaters are used to extend transmissions so that the signal can cover longer distances or be received on the other side of an obstruction. Some types of repeaters broadcast an identical signal, but alter its method of transmission, for example, on another frequency or baud rate.
There are several different types of repeaters; a telephone repeater is an amplifier in a telephone line, an optical repeater is an optoelectronic circuit that amplifies the light beam in an optical fiber cable; and a radio repeater is a radio receiver and transmitter that retransmits a radio signal.
The International Telecommunication Union definition is a communications channel that operates in one direction at a time, but that may be reversible; this is termed half duplex in other contexts. A duplex communication channel requires two simplex channels operating in opposite directions.
For example, in TV and radio broadcasting, information flows only from the transmitter site to multiple receivers. A pair of walkie-talkie two-way radios provide a simplex circuit in the ITU sense; only one party at a time can talk, while the other listens until it can hear an opportunity to transmit. The transmission medium (the radio signal over the air) can carry information in only one direction.
The old Western Union company used the term simplex when describing the half-duplex and simplex capacity of their new transatlantic telegraph cable completed between Newfoundland and the Azores in 1928. The same definition for a simplex radio channel was used by the National Fire Protection Association in 2002.
Sound pressure or acoustic pressure is the local pressure deviation from the ambient (average or equilibrium) atmospheric pressure, caused by a sound wave. In air, sound pressure can be measured using a microphone, and in water with a hydrophone. The SI unit of sound pressure is the pascal (Pa).
The lower limit of audibility is defined as SPL of 0 dB, but the upper limit is not as clearly defined. While 1 atm (194 dB peak or 191 dB SPL) is the largest pressure variation an undistorted sound wave can have in Earth’s atmosphere (i.e. if the thermodynamic properties of the air are disregarded, in reality the sound wave become progressively non-linear starting over 150 dB), larger sound waves can be present in other atmospheres or other media such as under water or through the Earth.
Equal-loudness contour, showing sound-pressure-vs-frequency at different perceived loudness levels
Ears detect changes in sound pressure. Human hearing does not have a flat spectral sensitivity (frequency response) relative to frequency versus amplitude. Humans do not perceive low- and high-frequency sounds as well as they perceive sounds between 3,000 and 4,000 Hz, as shown in the equal-loudness contour. Because the frequency response of human hearing changes with amplitude, three weightings have been established for measuring sound pressure: A, B and C. A-weighting applies to sound pressures levels up to 55 dB, B-weighting applies to sound pressures levels between 55 dB and 85 dB, and C-weighting is for measuring sound pressure levels above 85 dB.
Time-division multiple access (TDMA) is a channel access method for shared-medium networks. It allows several users to share the same frequency channel by dividing the signal into different time slots.[1] The users transmit in rapid succession, one after the other, each using its own time slot. This allows multiple stations to share the same transmission medium (e.g. radio frequency channel) while using only a part of its channel capacity. Dynamic TDMA is a TDMA variant that dynamically reserves a variable number of time slots in each frame to variable bit-rate data streams, based on the traffic demand of each data stream.
A monopole antenna is a class of radio antenna consisting of a straight rod-shaped conductor, often mounted perpendicularly over some type of conductive surface, called a ground plane.[1][2][3] The driving signal from the transmitter is applied, or for receiving antennas the output signal to the receiver is taken, between the lower end of the monopole and the ground plane. One side of the antenna feedline is attached to the lower end of the monopole, and the other side is attached to the ground plane, which is often the Earth. This contrasts with a dipole antenna which consists of two identical rod conductors, with the signal from the transmitter applied between the two halves of the antenna.
in radio communication, an omnidirectional antenna is a class of antenna which radiates equal radio power in all directions perpendicular to an axis (azimuthal directions), with power varying with angle to the axis (elevation angle), declining to zero on the axis. When graphed in three dimensions (see graph) this radiation pattern is often described as doughnut-shaped. Note that this is different from an isotropic antenna, which radiates equal power in all directions, having a spherical radiation pattern. Omnidirectional antennas oriented vertically are widely used for nondirectional antennas on the surface of the Earth because they radiate equally in all horizontal directions, while the power radiated drops off with elevation angle so little radio energy is aimed into the sky or down toward the earth and wasted. Omnidirectional antennas are widely used for radio broadcasting antennas, and in mobile devices that use radio such as cell phones, FM radios, walkie-talkies,
Digital mobile radio (DMR) is a limited open digital mobile radio standard defined in the European Telecommunications Standards Institute (ETSI) Standard TS 102 361 parts 1–4 and used in commercial products around the world. DMR, along with P25 phase II and NXDN are the main competitor technologies in achieving 6.25 kHz equivalent bandwidth using the proprietary AMBE+2 vocoder. DMR and P25 II both use two-slot TDMA in a 12.5 kHz channel, while NXDN uses discrete 6.25 kHz channels using frequency division and TETRA uses a four-slot TDMA in a 25 kHz channel.
DMR was designed with three tiers. DMR tiers I and II (conventional) were first published in 2005, and DMR III (Trunked version) was published in 2012, with manufacturers producing products within a few years of each publication.
