Research, Design, and Prototyping: SDR Design

SIGINT’s (Signals Intelligence) current operational environment often requires rapid development of waveforms, protocols, and devices to dependably function in different environments. The best solutions for such functions are Software Defined Radios (SDR), which are the principal solution to prototype wireless communication systems leading to better solutions quickly. NI has adequately identified the following requirements to fulfill client needs and specifications:

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Fiber Optics

Fiber optics use hair-like glass fibers to cany modulated light to transmit signals over distances. Light signal systems use simpler equipment, less energy, and are less prone to interference. The glass fiber has a clear core to carry the light and a cladding that is highly reflective, as well as a protective coating. Light beamed into the core is reflected from side to side to keep it moving down the core. An electronic signal, such as a telephone signal, is converted to a light beam by a light generator, which can be a light-emitting diode (LED) or a laser diode. The light is transmitted down the fiber through various optical connectors, jumpers, patch panels, etc., and is picked up at the receiving end by a photodetector that converts it back to an electronic signal. Long cable runs use weld-like splices. Clear optical continuity is needed for light transmission.

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Insulation and Dielectric Testers

A dielectric is an insulating material, but it is an insulating material that has been manufactured with certain electrical characteristics to interact with other electrical characteristics of a component to give the component its ratings. The insulating material between the plates of a capacitor is a dielectric. It helps determine the capacitance value and must resist voltage breakdown at the rated voltage of the capacitor.

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Power Meters

Calculating Power

If you wish to find power dissipated in an electrical load, measure any two of the three basic electrical quantities- current, voltage, and resistance. For example, you will recall that power can be calculated by multiplying voltage by current: P = VI. Therefore, if you use a voltmeter to measure the voltage across a load, and a current meter to measure the current flowing through the load, insert these values into the power equation. Similarly, you can measure current through the load and the resistance of the load, and then calculate power with: P = 12 R. Or you can measure the voltage across the load and use the equation: p = y2; R.

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Digital Meters

Input circuits allow the input voltage to be stepped down by the ranging circuits, which could be a switch or automatic circuits. The ranging circuits also select the proper pulse stream from the clock and divider circuits. The test voltage is amplified and integrated with the gate pulse to produce a ramp voltage that will pass a selected sample of pulses. The number of pulses passed is related to the test voltage. These are shaped and counted, and then decoded to drive the seven-segment displays.

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Digital Circuits Part 2

The purpose of the integrator and gate circuits is to pass on the number of pulses that match the test voltage being measured. Since a specific pulse frequency stream is being applied to the gate, the test voltage must somehow control how long the gate will be allowed to pass the pulses; the higher the test voltage, the longer the gate will be open, and the more pulses will be passed through- and the number of pulses will represent the digitized version of the analog test voltage.

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Amplified Resistance Measurements

The electronic meter is used for resistance measurements in a manner similar to the way it is used for current measurements. Using the same types of amplifier stages as was used for the voltmeters and ammeters, where a 0.5-volt-signal produced a full-scale deflection, resistance circuits can be set up using standard battery source voltages supplying current to standard high­ precision resistance circuits, whose values are known. When the resistor under test is connected into the circuit, it will change the total resistance, resulting in a change in current flow, which produces a signal voltage that is directly related to the resistance under test.

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Amplified Current Measurements

To use the meter movement to make voltage and resistance measurements, the use of Ohm’s law is required so the current flow reading can be interpreted in terms of voltage or resistance. The amplified analog meter differs because the amplifier is voltage sensitive. As explained for amplified voltage measurements, a high input resistance is used with a range switch to tap down the voltage applied to the input of the amplifier stage. Since the amplified meter is a voltage sensitive device, the input circuit used for current measurements must convert the current to corresponding voltage levels and use Ohm’s law to interpret the related current flowing in the circuit under test.

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Amplified Input Voltmeter

The higher the ohms/volt rating of a voltmeter, the less the voltmeter will upset circuit conditions. And the less circuit conditions are upset, the more accurate the reading will be. Most of the higher-end voltmeters and multimeters available now are rated at about 20,000 ohms/volt; more accurate voltmeters are rated at 100,000 ohms/volt. In some of the high-resistance circuits found in some present-day equipment, however, even a meter rated at 20,000 ohms /volt will greatly upset circuit conditions, and result in an incorrect reading. While a 100,000 ohms/voltmeter will give more accurate readings, even more accuracy is needed with some circuits. To overcome this problem, a device with a high ohms/volt rating called an electronic voltmeter was developed.

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