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SUMMARY - 14193_140
ANSWERS TO QUESTIONS Q1. THROUGH Q8 - 14193_142

Neets Module 21-Test Methods and Practices
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4-13 Standing waves that are present on a transmission line can be used to determine the TRANSMITTER FREQUENCY. Voltage or current peaks are present at half-wavelength intervals. By measuring the distance between peaks, you can compute frequency mathematically. TWO-WIRE, PARALLEL TRANSMISSION LINES are usually tested for standing waves with test devices that are inductively coupled to the line. These test devices vary greatly in their complexity, ranging from bridge circuits to simple neon lamps. INSERTION LOSS MEASUREMENTS are performed by injecting a signal of a known amplitude into a transmission line and then monitoring the signal at the far end of the cable with a power meter. Loss measurements must be taken at various frequencies to determine if the transmission line is good across its frequency range. The most common cause of INTERMODULATION DISTORTION is improper spacing of transmitters and receivers. CROSS MODULATION is common to equipment that is misaligned. Intermodulation distortion can be tested by injecting two signals (different frequencies) into a piece of equipment and then monitoring its output for distortion using a spectrum analyzer. Intermodulation distortion is usually caused by improper antenna spacing or by poorly shielded components or circuits. REFERENCES EIMB, Test Methods and Practices Handbook, NAVSEA 0967-LP-000-0130, Naval Sea Systems Command, Washington, D.C., 1980. NEETS, Module 10, Wave Propagation, Transmission Lines, and Antennas, NAVEDTRA 172-10-00-83, Naval Education Training and Program Development Center, Pensacola, Fla., 1983. SWR Meter 415E, NAVSHIPS 0969-139-2010, Hewlett-Packard Co., Palo Alto, Calif. 1968.






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