Handheld Spectrum Analyzer

To examine spectral composition of wave form such as electrical, acoustic or optical wave form, we can use spectrum analyzer. Spectral analyzer can also be used to measure power spectrum.

At this time, there are two type spectrum analyzer, analog and digital type :

• Analog Spectrum analyzer
  To measure the range of frequencies an analog spectrum amalyzer either use variable band pass filter whose mid frquency os automatically swept the range or superheterodyne receiver where the local oscilator is swept through a range of frequencies.

• Digital Spectrum Analyzer
  Discrete Fourier Transform, a mathematical transformation process is used in digital spectrum analyzer to transform a waveform into the component of its frequency spectrum.

Some type spectrum analyzer use mix process, first they use superheterodyne to down converted to a lower frequency and later analyzed using fast fourier transform.

A few years ago, spectrum analyzer has big size and not portable, at this time already availabe in market handheld spectrum analyzer. Some manufacturer such as Anritsu, Rohde & Schwarz, and Willtek produce handheld spectrum analyzer.

Willtek’s 9102 Handheld Spectrum Analyzer is a multifunction instrument designed for lab and field applications concerning scalar network and spectrum analysis, including cable and antenna measurements and EMC pre-qualification tests. The basic 9102 has a frequency range of 100 kHz to 4 GHz and a resolution bandwidth (RBW) of an exceptional 1 kHz. An optional frequency extension allows measurements up to 7.5 GHz. The 9102 is small in size and weight, with a large, bright display and easy-to-use menu structure.

Anritsu MS2711D Handheld Spectrum Analyzer covering the 100 kHz to 3.0 GHz frequency range, the MS2711D handheld spectrum analyzer is the proven solution for installing, provisioning, maintaining and troubleshooting wireless systems and RF frequency spectrum interference issues. This portable spectrum analyzer features a built-in standard preamplifier in a compact, handheld design that can go “anywhere, anytime” with no backpack required. Ideal for field environments and applications that require mobility, such as site surveys and on-site system testing. The MS2711D can be ordered with optional built-in transmission measurement that adds scalar analysis capability from 25 MHz to 2.5 GHz.

Static electricity

It was discovered centuries ago that certain types of materials would mysteriuosly attract one another after being rubbed together. For example, after rubbing a piece if silk against a piece of glass, the silk an glass would tend to stick together. Indeed, there was an attractive force that could be demonstrated even when the two materials we seperated. Glass and silk aren't the only materils known to behave like this. Anyone who has ever brushed up agaist a latex baloon only to find that it tries to stick to then has experienced this same phenomenon. Paraffin wax and wool cloth are another pair of materials early experimenters recognized as manifesting attractive forces after eing rubed together. This phenomenon became even more interesting when it was discovered that identical materials, after having been rubbed with their respective cloths, always repelled each other. It was also noted that when a piece of glass rubbed with silk was exposed to a piece of wax rubbed with wool, the two materials would attract to one another. Furthermore, it was found that any material demonstrating properties of attraction or repulsion after being rubbed could be classed into one of two distinct categories:attracted to glass and repelled by wax, or repelled by glass and attracted to wax. It was either one or the other, there were no materials found that would be attracted to or repelled by both glss and wax, or that ractd to one without reacting to the other.

Thyristor

A thyristor is a controlled rectifier where the unidirectional current flow from anode to cathode is initiated by a small signal current from gate to cathode.

Turn-on
A thyristor is turned on by making its gate positive with respect to its cathode, thereby causing current flow into the gate. When the gate voltage reaches the threshold voltage VGT and the resulting current reaches the threshold current IGT, within a very short time known as the gate-controlled turn-on time, tgt, the load current can flow from ’a’ to ’k’. If the gate current consists of a very narrow pulse, say less than 1μs, its peak level will have to increase for progressively narrower pulse widths to guarantee triggering.
When the load current reaches the thyristor’s latching current IL, load current flow will be maintained even after removal of the gate current. As long as adequate load current continues to flow, the thyristor will continue to conduct without the gate current. It is said to be latched ON. Note that the VGT, IGT and IL specifications given in data are at 25 °C. These parameters will increase at lower temperatures, so the drive circuit must provide adequate voltage and current amplitude and duration for the lowest expected operating temperature.

Rule 1. To turn a thyristor (or triac) ON, a gate current ≥ IGT must be applied until the load current is ≥ IL. This condition must be met at the lowest expected operating temperature.

Sensitive gate thyristors such as the Bt150 can be prone to turn-on by anode to cathode leakage current at high temperatures. If the junction temperature Tj is increased above Tj max, a point will be reached where the leakage current will be high enough to trigger the thyristor’s sensitive gate. It will then have lost its ability to remain in the blocking state and conduction will commence without the application of an external gate current.
This method of spurious turn-on can be avoided by using one or more of the following solutions: 1. Ensure that the temperature does not exceed Tj max. 2. Use a thyristor with a less sensitive gate such as the Bt151, or reduce the existing thyristor’s sensitivity by including a gate-to-cathode resistor of 1kÙ or less. 3. If it is not possible to use a less sensitive thyristor due to circuit requirements, apply a small degree of reverse biasing to the gate during the ’off’ periods. This has the effect of increasing IL. During negative gate current flow, particular attention should be paid to minimising the gate power dissipation.

Turn-off (commutation)
In order to turn the thyristor off, the load current must be reduced below its holding current IH for sufficient time to allow all the mobile charge carriers to vacate the junction. This is achieved by "forced commutation" in DC circuits or at the end of the conducting half cycle in AC circuits. (Forced commutation is when the load circuit causes the load current to reduce to zero to allow the thyristor to turn off.) At this point, the thyristor will have returned to its fully blocking state. If the load current is not maintained below IH for long enough, the thyristor will not have returned to the fully blocking state by the time the anode-to-cathode voltage rises again. It might then return to the conducting state without an externally-applied gate current. Note that IH is also specified at room temperature and, like IL, it reduces at higher temperatures. The circuit must therefore allow sufficient time for the load current to fall below IH at the maximum expected operating temperature for successful commutation.

Rule 2. To turn off (commutate) a thyristor (or triac), the load current must be < IH for sufficient time to allow a return to the blocking state. This condition must be met at the highest expected operating temperature.

Diode

A diode is a semiconductor device which allows current to flow through it in only one direction. Diodes are the most widely used devices in low- and high-speed electronic circuits and in rectifiers and power supplies. Other applications are in voltage regulators, detectors, and demodulators. There are some type of diode that can be used for different purpose.

Zener Diode
Zener diodes is specially built to operate in reverse breakdown. Zener diode operate in the reverse direction. Zener diode usually used for voltage stabilization.

Varactor Diodes
The varactor diode is an ordinary pn-diode that uses the voltage-dependent variable capacitance of the diode. The varactor diode is widely used as a voltage-dependent capacitor in electronically tuned radio receivers and in TV.

Tunnel Diodes
The tunnel diode is an ordinary pn-junction diode with very heavy doped n and p regions. Because the junction is very thin, a tunnel effect takes place. An electron can tunnel through the thin depletion layer from the conduction band of the n region directly into the valence band of the p region. Tunnel diodes create a negative differential resistance in the forward direction, due to the tunnel effect. Tunnel diodes are used as mixers, oscillators, amplifiers, and detectors. They operate at very high frequencies in the gigahertz bands.

Inductors

Inductance is used for the storage of magnetic energy. Magnetic energy is stored as long as current keeps flowing through the inductor. In a perfect inductor, the current of a sine wave lags the voltage by 90°. Inductance measured in Henry

Coil Inductance
Inductance is related to the turns in a coil as follows:
1. The inductance is proportional to the square of the turns.
2. The inductance increases as the length of the winding is increased.
3. A shorted turn decreases the inductance, affects the frequency response, and increases the insertion loss.
4. The inductance increases as the permeability of the core material increases.
5. The inductance increases with an increase in the cross-sectional area of the core material.
6. Inductance is increased by inserting an iron core into the coil.
7. Introducing an air gap into a choke reduces the inductance.

Capacitor

Capacitor is an electrical device that can store electrical energy. Capacitance is the concept of energy storage in an electric field and is restricted to the area, shape, and
spacing of the capacitor plates and the property of the material separating them. Capacitance measured in Farad. Capacitor that we usually used in micro, pico, or nano Farad.
Capacitors are used to filter, couple, tune, block dc, pass ac, bypass, shift phase, compensate, feed through, isolate, store energy, suppress noise, and start motors. They must also be small, lightweight, reliable, and withstand adverse conditions.

Breakdown voltage
Capacitor have parameter that called breakdown voltage. Break down voltage is the maximum voltage that can apply to a capacitor. When we applied voltage larger than break down voltage, capacitor will damaged and some times can be exploded.

Types of Capacitors
Ceramic Capacitors
Ceramic capacitors are used most often for bypass and coupling applications. Ceramic capacitor have capacitance range from 1.0pF to 4.7uF. Ceramic capacitors have no polarity.
Ceramic capacitors should not be used for analog circuits, because they can distort the signal.

Film Capacitors
Film capacitors consist of alternate layers of metal foil and one or more layers of a flexible plastic insulating material (dielectric) in ribbon form rolled and encapsulated.

Mica Capacitors
Mica capacitors have small capacitance values and are usually used in high-frequency circuits. They are constructed as alternate layers of metal foil and mica insulation, which are stacked and encapsulated, or are silvered mica, where a silver electrode is screened on the mica insulators.

Paper-Foil-Filled Capacitors
Paper-foil-filled capacitors are often used as motor capacitors and are rated at 60 Hz. They are made of alternate layers of aluminum and paper saturated with oil that are rolled together. The assembly is mounted in an oil filled, hermetically sealed metal case.

Electrolytic Capacitors
Electrolytic capacitors provide high capacitance in a tolerable size; however, they do have drawbacks. Low temperatures reduce performance, while high temperatures dry them out. The electrolytes themselves can leak and corrode the equipment. Repeated surges above the rated working voltage, excessive ripple currents, and high operating temperature reduce performance and shorten capacitor life. Electrolytic capacitors are manufactured by an electro chemical formation of an oxide film on a metal surface.
The metal on which the oxide film is formed serves as the anode or positive terminal of the capacitor; the oxide film is the dielectric, and the cathode or negative terminal is either a conducting liquid or a gel.

Resistor

Resistor is an electronic device that have function to reduce the electric current. The magnitude to the opposition to flow current is called resistance in the resistor. Resistance is measured in ohm. An ohm is the resistance that arises when a current of one ampere is passed through a resistor subjected to one volt across its terminals.
There are three type of resistor, fixed and variable, and special purpose resistor. Resistor also classified according to the material which they are made for. Usually resistor is made of carbon film or metal film. There are other thing that need to consider when selecting a resistor, resistor tolerance and power rating. Resistor tolerance specified in % and maximum power rating of resistor is specified in watt.

Fixed resistor
Composition Resistors
Composition resistors are composed of carbon particles mixed with a binder. This mixture is molded into a cylindrical shape and hardened by baking. Leads are attached axially to each end, and the assembly is encapsulated in a protective encapsulation coating. Color bands on the outer surface indicate the resistance value and tolerance. Composition resistors are economical and exhibit low noise levels for resistances above 1 MW. Composition resistors are usually rated for temperatures in the neighborhood of 70°C for power ranging from 1/8 to 2 W. Composition resistors have end-to-end shunted capacitance that may be noticed at frequencies in the neighborhood of 100 kHz, especially for resistance values above 0.3 MW.

Metal film resistors
Metal film resistors are used when a higher tolerance (more accurate value) is needed. They are much more accurate in value than carbon film resistors. They have about ±0.05% tolerance. They have about ±0.05% tolerance. Resistors that are about ±1% are more than sufficient. Metal-film resistors are commonly made of nichrome, tin-oxide, or tantalum nitride, either hermetically sealed or using molded-phenolic cases. The metal film resistor is used for bridge circuits, filter circuits, and low-noise analog signal circuits.

Wire-Wound Resistors
Wire-wound resistors are made by winding wire of nickel-chromium alloy on a ceramic tube covering with a vitreous coating. The spiral winding has inductive and capacitive characteristics that make it unsuitable for operation above 50 kHz. The frequency limit can be raised by non inductive winding so that the magnetic fields produced by the two parts of the winding cancel.

Variable Resistors
Potentiometers
The potentiometer is a special form of variable resistor with three terminals. Two terminals are connected to the opposite sides of the resistive element, and the third connects to a sliding contact that can be adjusted as a voltage divider. Potentiometers are usually circular in form with the movable contact attached to a shaft that rotates. Potentiometers are manufactured as carbon composition, metallic film, and wire-wound resistors available in single-turn or multi turn units. The movable contact does not go all the way toward the end of the resistive element, and a small resistance called the hop-off resistance is present to prevent accidental burning of the resistive element.

Rheostat
The rheostat is a current-setting device in which one terminal is connected to the resistive element and the second terminal is connected to a movable contact to place a selected section of the resistive element into the circuit. Typically, rheostats are wire-wound resistors used as speed controls for motors, ovens, and heater controls and in applications where adjustments on the voltage and current levels are required, such as voltage dividers and bleeder circuits.

Special-Purpose Resistors
LDR (Light Dependent Resistor)
LDR is a device whose resistance changes in response to the amount of light falling on it. An LDR's resistance value in the presence strong light is just a few ohms, but in the absence of light the value can be many tens of mega ohms. It is important to note that they are not very linear in their response. The base material from which LDRs made is cadmium sulfide or lead sulphated.

Thermistor
Thermistors are resistors that change their resistance exponentially with changes in temperature. If the resistance decreases with increase in temperature, the resistor is called a negative temperature coefficient (NTC) resistor. If the resistance increases with temperature, the resistor is called a positive temperature coefficient (PTC) resistor.