Tektronix 494A O o o o o o, Frequencyterms, Amplitudeterms, Gfoesary- 494l4g4Ap Service,Vol

Gfoesary- 494[l4g4Ap Service,Vol. 1

FREQUENCYTERMS

DisplayFrequency.The inputfrequencyas indicatedby the spectrumanalyzerand expressedi; hertz.

Frequency Span (Dispersion).The magnitudeof the frequencyband displayed,expressedin-hertzor hertz per division.

FrequencyLlnearityError.The error of the relationship betweenthe frequencyof the input signaland the fre- quencydisplayed(expressedas a ratio).

FreguencyDrlft Gradualshift or change in displayed frequency over the specified time Oue to internal changesin the spectrumanalyzer,and expressedin hertz per second,where other conditionsremaincon- stant.

lmpulse Bandwldth.The displayedspectrallevelof an applied pulse divided by its spectral voltage density levelassumedto be flat withinthe pass_band.

ResidualFM (lncidentalFM). Shortterm displayedfre- quencyinstabilityor jitter due to instabilityin th-espec_trum analyzerlocaloscillators,givenin termsof pLak- to-peakfrequencydeviationand expressedin hertz or percentof the displayedfrequency.

Shape Factor (Skirt Selectivlty).The ratio of the fre_ quencyseparationof the two (60dBi6 dB) down points on the response curve to the static resolution bandwidth.

Static (Amplifier)ResolutlonBandwldth.ThE specified bandwidthof the spectrumanalyzer'sresponseto a cw signal, if sweep time is kept substantiailylong. This bandwidthis the frequencyseparationof two pointson the responsecuryerusually6 dB down,if it is measured eitherby manualscan(truestaticmethod)or by usinga verylow speedsweep(quasi-staticmethod).

Zeto Pip (Response). An output indication which correspondsto zero inputfrequency.

AMPLITUDETERMS

Detlectlon Coeflicient. The ratio of the input signal rnagnitude to the resultant output indication. Tne ratio may be expressed in terms of volts (rms) per division, decibels per division, watts per division, or any other specified factor.

Dlsplay Reference Level A designated vertical position representing a specified input level. The level may be expressedin dBm, volts, or any other units.

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Display Flatness. The unwanted variation of the displayedamplitudeover a specifiedfrequencyspan, expressedin decibels.

Relative Display Flatness. The display ftatness measuredrelativeto the displayamplitudeat a fixed frequencywithinthe frequencyspan,expressedin decibels.

Display flatness is closely related to fre- quency response. The main difference is that the spectrumdisplay is not recentered.

Display Law. The mathematical law that d€fines the input-output function of the instrument.

The following cases apply:

Llnear - A display in which the scale divi- sions are a linear function of the input sig- nalvoltage .

Square law {power} - A display in which the scale divisions are a linear function of the input signalpower.

Logarithmic - A display in which the scale divisions are a logarithmic function of the input signal voltage.

Dynamic Range. The maximum ratio of the levels of two signals simultaneouslypresent at the input which can be measured to a specified accuracy.

Display Dynamic Range. The maximum ratio of the levels of two non-harmonicallyrelated sinusoidal signals each of which can be simultaneouslymeas- ured on the screen to a specified accuracy.

Frequency Response. The unwanted variation of the displayed amplitude over a specified center frequency range, measured at the center frequency,expressed in decibels .

Gain Compresslon. Effect seen at an input level where the analyzercircuits have less gain than their small sig- nal values. This is usually specified at the 1 dB compressionpoint in terms of the input levelrequiredto reduce the gain by 1 dB.

Input lmpedance. The impedance at the desired input terminal. Usually expressed in terms of vswr, return loss, or other related terms for low impedancedevices and resistance-capacitance parameters for high impedancedevices.

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