A time-domain reflectometer is an electronic instrument that uses time-domain reflectometry to characterize and locate faults in metallic cables. It can be used to locate discontinuities in a connector, printed circuit board, or any other electrical path; the equivalent device for optical fiber is an optical time-domain reflectometer. A TDR measures reflections along a conductor. In order to measure those reflections, the TDR will transmit an incident signal onto the conductor and listen for its reflections. If the conductor is of a uniform impedance and is properly terminated there will be no reflections and the remaining incident signal will be absorbed at the far-end by the termination. Instead, if there are impedance variations some of the incident signal will be reflected back to the source. A TDR is similar in principle to radar; the reflections will have the same shape as the incident signal, but their sign and magnitude depend on the change in impedance level. If there is a step increase in the impedance the reflection will have the same sign as the incident signal.
The magnitude of the reflection depends not only on the amount of the impedance change, but upon the loss in the conductor. The reflections are measured at the output/input to the TDR and displayed or plotted as a function of time. Alternatively, the display can be read as a function of cable length because the speed of signal propagation is constant for a given transmission medium; because of its sensitivity to impedance variations, a TDR may be used to verify cable impedance characteristics and connector locations and associated losses, estimate cable lengths. TDRs use different incident signals; some TDRs transmit a pulse along the conductor. Narrow pulses can offer good resolution, but they have high frequency signal components that are attenuated in long cables; the shape of the pulse is a half cycle sinusoid. For longer cables, wider pulse widths are used. Fast rise time steps are used. Instead of looking for the reflection of a complete pulse, the instrument is concerned with the rising edge, which can be fast.
A 1970s technology TDR used steps with a rise time of 25 ps. Still other TDRs detect reflections with correlation techniques. See spread-spectrum time-domain reflectometry; these traces were produced by a time-domain reflectometer made from common lab equipment connected to 100 feet of coaxial cable having a characteristic impedance of 50 ohms. The propagation velocity of this cable is 66% of the speed of light in a vacuum; these traces were produced by a commercial TDR using a step waveform with a 25 ps risetime, a sampling head with a 35 ps risetime, an 18-inch SMA cable. The far end of the SMA cable was left connected to different adapters, it takes about 3 ns for the pulse to travel down the cable and reach the sampling head. A second reflection can be seen in some traces. Consider the case where the far end of the cable is shorted; when the rising edge of the pulse is launched down the cable, the voltage at the launching point "steps up" to a given value and the pulse begins propagating down the cable towards the short.
When the pulse hits the short, no energy is absorbed at the far end. Instead, an opposing pulse reflects back from the short towards the launching end, it is only when this opposing reflection reaches the launch point that the voltage at this launching point abruptly drops back to zero, signalling the fact that there is a short at the end of the cable. That is, the TDR has no indication that there is a short at the end of the cable until its emitted pulse can travel down the cable at the speed of light and the echo can return up the cable at the same speed, it is only after this round-trip delay that the short can be perceived by the TDR. Assuming that one knows the signal propagation speed in the particular cable-under-test in this way, the distance to the short can be measured. A similar effect occurs. In this case, the reflection from the far end is polarized identically with the original pulse and adds to it rather than cancelling it out. So after a round-trip delay, the voltage at the TDR abruptly jumps to twice the originally-applied voltage.
Note that a theoretical perfect termination at the far end of the cable would absorb the applied pulse without causing any reflection. In this case, it would be impossible to determine the actual length of the cable. Luckily, perfect terminations are rare and some small reflection is nearly always caused; the magnitude of the reflection is referred to as the reflection coefficient or ρ. The coefficient ranges from 1 to -1; the value of zero means. The reflection coefficient is calculated as follows: ρ = Z t − Z o Z t + Z o Where Zo is defined as the characteristic impedance of the transmission medium and Zt is the impedance of the termination at the far end of the transmission line. Any discontinuity can be viewed as a termination impe
Peak programme meter
A peak programme meter is an instrument used in professional audio that indicates the level of an audio signal. Different kinds of PPM fall into broad categories: True peak programme meter; this shows the peak level of the waveform. Quasi peak programme meter; this only shows the true level of the peak if it exceeds a certain duration a few milliseconds. On peaks of shorter duration, it indicates less than the true peak level; the extent of the shortfall is determined by the'integration time'. Sample peak programme meter; this is a PPM for digital audio --. It may have either a'true' or a'quasi' integration characteristic. Over-sampling peak programme meter; this is a sample PPM in which the signal has first been over-sampled by a factor of four, to alleviate the problem with a basic sample PPM. In professional usage, where consistent level measurements are needed across an industry, audio level meters comply with a detailed formal standard; this ensures. The principal standard for PPMs is IEC 60268-10.
It describes two different quasi-PPM designs that have roots in meters developed in the 1930s for the AM radio broadcasting networks of Germany and the United Kingdom. The term Peak Programme Meter refers to these IEC-specified types and similar designs. Though designed for monitoring analogue audio signals, these PPMs are now used with digital audio. PPMs do not provide effective loudness monitoring. Newer types of meter do, there is now a push within the broadcasting industry to move away from the traditional level meters in this article to two new types: loudness meters based on EBU Tech. 3341 and oversampling true PPMs. The former would be used to standardise broadcast loudness to −23 LUFS and the latter to prevent digital clipping. In common with many other types of audio level meter, PPMs used electro-mechanical displays; these took the form of moving-coil panel meters or mirror galvanometers with demanding'ballistics': the key requirement being that the indicated level should rise as as possible with negligible overshoot.
These displays require active driver electronics. Nowadays PPMs are implemented as'bargraph' incremental displays using solid-state illuminated segments in a vertical or horizontal array. For these, IEC 60268-10 requires a minimum of 100 segments and a resolution better than 0.5 dB at the higher levels. Many operators prefer the moving-coil meter type of display in which a needle moves in an arc, because an angular movement is easier for the human eye to monitor than the linear movement of a bargraph. PPMs can be implemented in software—in a general-purpose computer or by a dedicated device that inserts a PPM image into a picture signal for display on a picture monitor. A variety of terms such as'line-up level' and'operating level' exist, their meaning may vary from place to place. In an attempt bring clarity to level definitions in the context of programme transmission from one country to another, where different technical practices may apply, ITU-R Rec. BS.645 defined three reference levels: Measurement Level, Alignment Level and Permitted Maximum Level.
This document shows the reading corresponding to these levels for several types of meter. Alignment Level is the level of a steady sine-wave alignment tone. Permitted Maximum Level refers to the permitted maximum meter indication that operators should aim for on speech, music etc. not tone. PPMs use white-on-black displays, to minimise eyestrain with extended periods of use. PPMs are calibrated in one of these ways: In decibels relative to Alignment Level In decibels relative to Permitted Maximum Level In decibels relative to 0 dBu In decibels relative to 0 dBFS In simple numerical marks that can be correlated with any of the above Whichever scheme is used there is a scale mark corresponding to Alignment Level. Most PPMs have an logarithmic scale, i.e. linear in decibels, to provide useful indications over a wide dynamic range. Quasi-PPMs use a short integration time so they can register peaks longer than a few milliseconds in duration. In the original context of AM radio broadcasting in the 1930s, overloads due to shorter peaks were considered unimportant on the grounds that the human ear could not detect distortion due to momentary clipping.
Ignoring momentary clipping made it possible to increase average modulation levels. In modern digital audio practice, where quality standards are much higher than AM radio in the 1930s, clipping of short peaks is regarded as something to avoid. On typical, real-world audio signals, a quasi-PPM under-reads the true peak by 6 to 8 dB. Quasi-PPMs are still used in the digital age because of their usefulness in achieving programme balance. Overloads are avoided by allowing 9 dB of headroom when controlling digital levels with a quasi-PPM; the extent to which quasi-PPMs show less than the true amplitude of momentary peaks is determined by the'integration time'. This is defined by IEC 60268-10 as, "...the duration of a burst of sinusoidal voltage of 5000 Hz at reference level that results in an indication 2 dB below reference indication." This standard contains tables showing the difference between indicated and true peaks for tone bursts of other durations. The longer the integration time, the greater the difference between the true and indicated peaks.
In earlier standards, d
An LC circuit called a resonant circuit, tank circuit, or tuned circuit, is an electric circuit consisting of an inductor, represented by the letter L, a capacitor, represented by the letter C, connected together. The circuit can act as an electrical resonator, an electrical analogue of a tuning fork, storing energy oscillating at the circuit's resonant frequency. LC circuits are used either for generating signals at a particular frequency, or picking out a signal at a particular frequency from a more complex signal, they are key components in many electronic devices radio equipment, used in circuits such as oscillators, filters and frequency mixers. An LC circuit is an idealized model since it assumes there is no dissipation of energy due to resistance. Any practical implementation of an LC circuit will always include loss resulting from small but non-zero resistance within the components and connecting wires; the purpose of an LC circuit is to oscillate with minimal damping, so the resistance is made as low as possible.
While no practical circuit is without losses, it is nonetheless instructive to study this ideal form of the circuit to gain understanding and physical intuition. For a circuit model incorporating resistance, see RLC circuit; the two-element LC circuit described above is the simplest type of inductor-capacitor network. It is referred to as a second order LC circuit to distinguish it from more complicated LC networks with more inductors and capacitors; such LC networks with more than two reactances may have more than one resonant frequency. The order of the network is the order of the rational function describing the network in the complex frequency variable s; the order is equal to the number of L and C elements in the circuit and in any event cannot exceed this number. An LC circuit, oscillating at its natural resonant frequency, can store electrical energy. See the animation. A capacitor stores energy in the electric field between its plates, depending on the voltage across it, an inductor stores energy in its magnetic field, depending on the current through it.
If an inductor is connected across a charged capacitor, current will start to flow through the inductor, building up a magnetic field around it and reducing the voltage on the capacitor. All the charge on the capacitor will be gone and the voltage across it will reach zero. However, the current will continue; the current will begin to charge the capacitor with a voltage of opposite polarity to its original charge. Due to Faraday's law, the EMF which drives the current is caused by a decrease in the magnetic field, thus the energy required to charge the capacitor is extracted from the magnetic field; when the magnetic field is dissipated the current will stop and the charge will again be stored in the capacitor, with the opposite polarity as before. The cycle will begin again, with the current flowing in the opposite direction through the inductor; the charge flows back and forth through the inductor. The energy oscillates back and forth between the capacitor and the inductor until internal resistance makes the oscillations die out.
The tuned circuit's action, known mathematically as a harmonic oscillator, is similar to a pendulum swinging back and forth, or water sloshing back and forth in a tank. The natural frequency is determined by the inductance values. In most applications the tuned circuit is part of a larger circuit which applies alternating current to it, driving continuous oscillations. If the frequency of the applied current is the circuit's natural resonant frequency, resonance will occur, a small driving current can excite large amplitude oscillating voltages and currents. In typical tuned circuits in electronic equipment the oscillations are fast, from thousands to billions of times per second. Resonance occurs when an LC circuit is driven from an external source at an angular frequency ω0 at which the inductive and capacitive reactances are equal in magnitude; the frequency at which this equality holds for the particular circuit is called the resonant frequency. The resonant frequency of the LC circuit is ω 0 = 1 L C where L is the inductance in henrys, C is the capacitance in farads.
The angular frequency ω0 has units of radians per second. The equivalent frequency in units of hertz is f 0 = ω 0 2 π = 1 2 π L C; the resonance effect of the LC circuit has many important applications in signal processing and communications systems. The most common application of tank circuits is tuning radio receivers. For example, when we tune a radio to a particular station, the LC circuits are set at resonance for that particular carrier frequency. A series resonant circuit provides voltage magnification. A parallel resonant circuit provides current magnification. A parallel resonant circuit can be used as load impedance in output circuits of RF amplifiers. Due to high impedance, the gain of amplifier is maximum at resonant frequency
A galvanometer is an electromechanical instrument used for detecting and indicating an electric current. A galvanometer works as an actuator, by producing a rotary deflection, in response to electric current flowing through a coil in a constant magnetic field. Early galvanometers were not calibrated, but their developments were used as measuring instruments, called ammeters, to measure the current flowing through an electric circuit. Galvanometers developed from the observation that the needle of a magnetic compass is deflected near a wire that has electric current flowing through it, first described by Hans Christian Ørsted in 1820, they were the first instruments used to measure small amounts of electric currents. André-Marie Ampère, who gave mathematical expression to Ørsted's discovery and named the instrument after the Italian electricity researcher Luigi Galvani, who in 1791 discovered the principle of the frog galvanoscope – that electric current would make the legs of a dead frog jerk.
Sensitive galvanometers have been essential for the development of science and technology in many fields. For example, they enabled long range communication through submarine cables, such as the earliest Transatlantic telegraph cables, were essential to discovering the electrical activity of the heart and brain, by their fine measurements of current. Galvanometers had widespread use as the visualising part in other kinds of analog meters, for example in light meters, VU meters, etc. where they were used to measure and display the output of other sensors. Today the main type of galvanometer mechanism, still in use, is the moving coil, D'Arsonval/Weston type. Modern galvanometers, of the D'Arsonval/Weston type, are constructed with a small pivoting coil of wire, called a spindle, in the field of a permanent magnet; the coil is attached to a thin pointer. A tiny torsion spring pulls the pointer to the zero position; when a direct current flows through the coil, the coil generates a magnetic field.
This field acts against the permanent magnet. The coil twists, pushing against the spring, moves the pointer; the hand points at a scale indicating the electric current. Careful design of the pole pieces ensures that the magnetic field is uniform, so that the angular deflection of the pointer is proportional to the current. A useful meter contains provision for damping the mechanical resonance of the moving coil and pointer, so that the pointer settles to its position without oscillation; the basic sensitivity of a meter might be. Such meters are calibrated to read some other quantity that can be converted to a current of that magnitude; the use of current dividers called shunts, allows a meter to be calibrated to measure larger currents. A meter can be calibrated as a DC voltmeter if the resistance of the coil is known by calculating the voltage required to generate a full scale current. A meter can be configured to read other voltages by putting it in a voltage divider circuit; this is done by placing a resistor in series with the meter coil.
A meter can be used to read resistance by placing it in series with a known voltage and an adjustable resistor. In a preparatory step, the circuit is completed and the resistor adjusted to produce full scale deflection; when an unknown resistor is placed in series in the circuit the current will be less than full scale and an appropriately calibrated scale can display the value of the unknown resistor. These capabilities to translate different kinds of electric quantities, in to pointer movements, make the galvanometer ideal for turning output of other sensors that outputs electricity, into something that can be read by a human; because the pointer of the meter is a small distance above the scale of the meter, parallax error can occur when the operator attempts to read the scale line that "lines up" with the pointer. To counter this, some meters include a mirror along the markings of the principal scale; the accuracy of the reading from a mirrored scale is improved by positioning one's head while reading the scale so that the pointer and the reflection of the pointer are aligned.
The largest use of galvanometers was of the D'Arsonval/Weston type used in analog meters in electronic equipment. Since the 1980s, galvanometer-type analog meter movements have been displaced by analog to digital converters for many uses. A digital panel meter contains an analog to numeric display; the advantages of a digital instrument are higher precision and accuracy, but factors such as power consumption or cost may still favour application of analog meter movements. Most modern uses for the galvanometer mechanism are in control systems. Galvanometer mechanisms are divided into moving coil galvanometers. Mirror galvanometer systems are used as beam positioning or beam steering elements in laser scanning systems. For example, for material processing with high-power lasers, closed loop mirror galvanometer mechanisms are used with servo control systems; these are high power galvanometers and the newest galvanometers designed for beam steering applications can have frequency responses over 10 kHz with appropriate servo technology.
Closed-loop mirror galvanometers are used in similar ways in stereolithography, laser sintering, laser engraving, laser beam welding, laser TVs, laser displays and in imaging applications
An LCR meter is a type of electronic test equipment used to measure the inductance and resistance of an electronic component. In the simpler versions of this instrument the impedance was measured internally and converted for display to the corresponding capacitance or inductance value. Readings should be reasonably accurate if the capacitor or inductor device under test does not have a significant resistive component of impedance. More advanced designs measure true inductance or capacitance, as well as the equivalent series resistance of capacitors and the Q factor of inductive components; the device under test is subjected to an AC voltage source. The meter measures the voltage across and the current through the DUT. From the ratio of these the meter can determine the magnitude of the impedance; the phase angle between the voltage and current is measured in more advanced instruments. The meter must assume a series model for these two elements. An ideal capacitor has no characteristics other than capacitance, but there are no physical ideal capacitors.
All real capacitors have a little inductance, a little resistance, some defects causing inefficiency. These can be seen as inductance or resistance in series with the ideal capacitor or in parallel with it, and so with inductors. Resistors can have inductance and capacitance as a consequence of the way they are constructed; the most useful assumption, the one adopted, is that LR measurements have the elements in series and that CR measurements have the elements in parallel. Leakage is a special case in capacitors, as the leakage is across the capacitor plates, that is, in series. An LCR meter can be used to measure the inductance variation with respect to the rotor position in permanent magnet machines. Handheld LCR meters have selectable test frequencies of 100 Hz, 120 Hz, 1 kHz, 10 kHz, 100 kHz for top end meters; the display resolution and measurement range capability will change with the applied test frequency since the circuitry is more sensitive or less for a given component as the test frequency changes.
Benchtop LCR meters sometimes have selectable test frequencies of more than 100 kHz. They include options to superimpose a DC voltage or current on the AC measuring signal. Lower end meters might offer the possibility to externally supply these DC voltages or currents while higher end devices can supply them internally. In addition benchtop meters allow the usage of special fixtures to measure SMD components, air-core coils or transformers. Inductance, capacitance and dissipation factor can be measured by various bridge circuits, they involve adjusting variable calibrated elements until the signal at a detector becomes null, rather than measuring impedance and phase angle. Early commercial LCR bridges used a variety of techniques involving the matching or "nulling" of two signals derived from a single source; the first signal was generated by applying the test signal to the unknown and the second signal was generated by using a combination of known-value R and C standards. The signals were summed through a detector.
When zero current was noted by changing the value of the standards and looking for a "null" in the panel meter, it could be assumed that the current magnitude through the unknown was equal to that of the standard and that the phase was the reverse. The combination of standards selected could be arranged to read out C and DF directly, the precise value of the unknown. An example of this is 1621 Capacitance Bridges. ESR meter Q meter "LCR Primer", IET Labs Inc. April 2012
A tube tester is an electronic instrument designed to test certain characteristics of vacuum tubes. Tube testers evolved along with the vacuum tube to satisfy the demands of the time, their evolution ended with the tube era; the first tube testers were simple units designed for specific tubes to be used in the battlefields of World War I by radio operators, so they could test the tubes of their communication equipment. The most modern testers perform a multitude of the below tests and are automated. Examples of modern testers include the Amplitrex AT1000, the Space-Tech Lab EasyTubeTester, the Maxi pre-amp tester and the maxi-matcher by maxi test and the new, somewhat more primitive, DIVO VT1000 by Orange Amplification. While the AT1000, EasyTubeTester and the Maxi-test brand testers offer precise measurements of transconductance/Gm and emissions/iP at full or near full voltages, the Orange tester offers a simple numerical quality scale; the EasyTubeTester has a unique feature of quick tube matching +/-percentage display.
The simplest tester is the filament continuity tester with a neon lamp connected in series with the filament/heater and a current limiting resistance fed directly by the mains. There is therefore no need to select the appropriate filament voltage for the particular tube under test, but this equipment will not identify tubes that may be faulty in other ways, nor indicate any degree of wear; the same checks can be made with a cheap multimeter's resistance test. The tube checker is the second-simplest of all tube testers after filament continuity testing. Tubes are used as a low power rectifier, with all elements other than filament connections connected together as the anode, at a fraction of its normal emission. By mistake referred to sometimes as Emission Tester because they are a crude measure of emission in directly heated types. Switches pins. Next in complexity is the emission tester, which treats any tube as a diode by connecting the cathode to ground, all the grids and plate to B+ voltage, feeding the filament with the correct voltage, an ammeter in series with either the plate or the cathode.
This measures emission, the current which the cathode is capable of emitting, for the given plate voltage, which can be controlled by a variable load resistor. Switches will need to select the correct filament voltage plus which pins belong to the filament and cathode. Older testers may call themselves Plate Conductance if the ammeter is in series with the plate, or Cathode Conductance if the meter is in series with the cathode; the problems of emission testers are: they do not measure key characteristics of tubes, like transconductance they do not perform the tests at real load and currents they test the tube under static conditions, which are not near the dynamic conditions the tube would work with in a real electronic device tubes with grids might not show the real emission because of hot spots in the cathode, hidden by the grids under normal conditions grids will be forward biased to some extent - some fine control grid wires are limited in their ability to withstand this the amount of current that should be considered "100%" has to be known and documented for each tube type The advantage of an emission tester is that from all types of tube testers, it provides the most reliable warning of tube wear-out.
If emission is at 70%, transconductance can be at 90% still, gain at 100%. The best and most popular version used by the German army was the Funke W19; the disadvantage of an emission tester is that it can test a good tube as bad, a bad tube as good, because it ignores other properties of the tube. A tube with low emission will work fine in most circuits, need not be replaced on that indication alone, unless it measures much lower than specified or if it indicates a short. A variation on the emission tester is the dynamic conductance tester, a type of tester developed by the Jackson Electrical Company of Dayton, Ohio; the main difference is the use of ‘proportional AC voltages’ in place of applying the current directly to the grids and plate. Emission testers have a short circuit test, just a variation of the continuity tester with a neon lamp, which allows to identify if there is any shortcut between the different pairs of electrodes. A tester of this type applies DC voltage to the tube being tested, datasheet values are verified under real conditions.
Some parametric testers apply AC voltage to the tube being tested, with verification under conditions which simulate DC operation. Examples include the AVO line of tube testers, along with the Funke W20 and the Neuberger RPG375; the mutual conductance tester tests the tube dynamically by applying bias and an AC voltage to the control grid, measuring the current obtained on the plate, while maintaining the correct DC voltages on the plate and screen grid. This setup measures the transconductance of the tube, indicated in micromhos. A full set of characteristic curves for vacuum tubes, for semiconductor devices, could be displayed on an oscilloscope screen by use of a plug-in adapter, or on a dedicated curve tracer. An example is the Tektronix 570. From the late 1920s until the early 1970s, many department stores, drug stores and grocery stores in the U. S. had a self-service tube-vending display. It consisted of a tube-tester atop a locked cabinet of tubes, with a flip chart of instructions. One would remove the tubes from a malfunctioning device, such as a radio or television, bring them to the stor
A signal generator is an electronic device that generates repeating or non-repeating electronic signals in either the analog or the digital domain. It is used in designing, testing and repairing electronic or electroacoustic devices, though it has artistic uses as well. There are many different types of signal generators with different purposes and applications and at varying levels of expense; these types include function generators, RF and microwave signal generators, pitch generators, arbitrary waveform generators, digital pattern generators and frequency generators. In general, no device is suitable for all possible applications. Traditionally, signal generators have been embedded hardware units, but since the age of multimedia PCs, programmable software tone generators have been available. In June 1928, the General Radio 403, was the first commercial signal generator marketed, it supported a frequency range of 500Hz to 1.5MHz. In April 1929, the first commercial frequency standard was marketed by General Radio with a frequency of 50KHz.
A function generator is a device. Such devices contain an electronic oscillator, a circuit, capable of creating a repetitive waveform.. The most common waveform is a sine wave, but sawtooth, step and triangular waveform oscillators are available as are arbitrary waveform generators. If the oscillator operates above the audio frequency range, the generator will include some sort of modulation function such as amplitude modulation, frequency modulation, or phase modulation as well as a second oscillator that provides an audio frequency modulation waveform. An arbitrary waveform generator is a sophisticated signal generator that generates arbitrary waveforms within published limits of frequency range and output level. Unlike a function generator that produces a small set of specific waveforms, an AWG allows the user to specify a source waveform in a variety of different ways. An AWG is more expensive than a function generator and has less bandwidth. An AWG is used in higher-end test applications.
New high-speed DACs provide up to 16-bit resolution at sample rates in excess of 1 GS/s. These devices provide the foundation for an AWG with the bandwidth and dynamic range to address modern radio and communication applications. In combination with a quadrature modulator and advanced digital signal processing, high-speed DACs can be applied to create a full-featured vector signal generator with high modulation bandwidth. Example applications include commercial wireless standards such as Wi-Fi, WiMAX and LTE, in addition to military standards such as those specified in the Joint Tactical Radio System initiative. Broad modulation bandwidth allows multi-carrier signal generation, necessary for testing receiver adjacent channel rejection. RF and microwave signal generators are used for testing components and test systems in a wide variety of applications including cellular communications, WiFi, WiMAX, GPS, audio and video broadcasting, satellite communications and electronic warfare. RF and microwave signal generators have similar features and capabilities, but are differentiated by frequency range.
RF signal generators range from a few kHz to 6 GHz, while microwave signal generators cover a much wider frequency range, from less than 1 MHz to at least 20 GHz. Some models go as high as 70 GHz with a direct coaxial output, up to hundreds of GHz when used with external waveguide source modules. RF and microwave signal generators can be classified further as vector signal generators. Analog signal generators based on a sine-wave oscillator were common before the inception of digital electronics, are still used. There was a sharp distinction in purpose and design of radio-frequency and audio-frequency signal generators. RFRF signal generators are capable of producing CW tones; the output frequency can be tuned anywhere in their frequency range. Many models offer various types of analog modulation, either as standard equipment or as an optional capability to the base unit; this could include FM, ΦM and pulse modulation. Another common feature is a built-in attenuator which makes it possible to vary the signal’s output power.
Depending on the manufacturer and model, output powers can range from -135 to +30 dBm. A wide range of output power is desirable, since different applications require different amounts of signal power. For example, if a signal has to travel through a long cable out to an antenna, a high output signal may be needed to overcome the losses through the cable and still have sufficient power at the antenna, but when testing receiver sensitivity, a low signal level is required to see how the receiver behaves under low signal-to-noise conditions. RF signal generators are available as benchtop instruments, rackmount instruments, embeddable modules and in card-level formats. Mobile, field-testing and airborne applications benefit from lighter, battery-operated platforms. In automated and production testing, web-browser access, which allows multi-source control, faster frequency switching speeds improve test times and throughput. RF signal generators are required for servicing and setting up analog radio receivers, are used for professional RF applications.
AFAudio-frequency signal generators generate signals above. An early example was the HP200A Audio Oscillator, the first