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Introduction to Test Equipment

Normal Indications Upon Power On

SECOND CONVERTER. - The second converter actually contains two converters. Only one of these two converters in this section is ever operational, and selected as a result of the measurement band currently being used. The selected converter will convert the frequency received from the first converter to a usable (110 MHz) IF signal, which is then provided to the third converter.

THIRD CONVERTER. - This converter takes the 110 MHz IF signal, amplifies it, and then converts it to the final IF of 10 MHz. This signal, in turn, is then passed on to the IF section.

IF Section

The IF section receives the final IF signal and uses it to establish the system resolution by using selective filtering. System resolution is selected under microcomputer control among five bandwidths (1 MHz, 100 kHz, 10 kHz, 1 kHz, and 100 Hz). The gain for all bands are then leveled and logarithmically amplified. This is done so that each division of signal change on the CRT display remains equal in change to every other division on the CRT. For example, in the 10-dB-per-division mode, each division of change is equal to a 10 dB difference, regardless of whether the signal appears at the top or bottom of the CRT. The signal needed to produce the video output to the display section is then detected and provided.

Display Section

The display section provides a representative display of the input signal on the CRT. It accomplishes this by performing the following functions:

Receives the video signals from the IF section and processes these signals to adjust the vertical drive of the CRT;
Receives the sweep voltages and processes these signals to produce the horizontal CRT drive plate voltage;
Receives character data information and generates CRT plate drive signals to display alpha and numeric characters on the CRT;
Receives control levels from the front panel beam controls and generates unblanking signals to control display presence, brightness, and focus.

The vertical deflection of the beam is increased as the output of the amplitude detector increases. The horizontal position is controlled by the frequency control section and is the frequency analyzed at that instant. The beam sweeps from left to right, low to high frequencies during its analysis. During this analysis, any time a signal is discovered, a vertical deflection will show the strength of the signal at the horizontal position that is the frequency. This results in a display of amplitude as a function of frequency.

Frequency Control Section

The frequency control section accomplishes the tuning of the first and second LOs within the converter section. The frequency immediately being analyzed is controlled by the current frequencies of the LOs. To analyze another frequency, you must change an LO frequency to allow the new frequency to be converted to a 10 MHz signal by the converter section. Periodically, the unit sweeps and analyzes a frequency range centered on the frequency set by the FREQUENCY knob. Adjusting the FREQUENCY knob will cause the LOs to be tuned to the new frequency. Only the LOs of the first two converters can be changed to vary the frequency being analyzed.

Digital Control Section

All the internal functions are controlled from the front panel through the use of a built-in microcomputer. The microcomputer uses an internal bus to receive or produce all communication or control to any section of the analyzer.

Power and Cooling Section

The main power supply provides almost all the regulated voltages required to operate the unit. The display section provides the high voltage necessary for CRT operation.

The cooling system allows fresh cool air to be routed to all sections of the unit in proportion to the heat that is generated by each section.

SPECTRUM ANALYZER FRONT PANEL CONTROLS, INDICATORS, AND CONNECTORS

This section will describe the function of the front panel controls, indicators, and connectors. For a complete description of each function, refer to table 6-1 while reviewing the front panel in figure 6-43. The numbers located in column 1 of table 6-1 equate to the same numbers found on the front panel of figure 6-43. Because most operational functions of this spectrum analyzer are microprocessor-controlled, they are switch-selected rather than adjusted.

Figure 6-43. - Spectrum analyzer front panel controls, indicators, and connectors.

Table 6-1. - Description of Front Panel Controls, Indicators, and Connectors

ITEM	FUNCTION	DESCRIPTION
1	INTENSITY	This knob controls the brightness of the CRT trace and the CRT readout display. The focus is electronically adjusted.
2	READOUT	This push button switches the readout display on and off. All spectrum analyzer parameters are displayed except TIME/DIV. The brightness for this display is proportional to the trace brightness and can be readjusted on internal controls only by a qualified technician.
3	GRATILLUM	This push button switches the graticule light on and off.
4	BASELINE CLIP	This push button, when activated, clips (subdues) the intensity at the baseline.
5	Triggering	This area allows one of four triggering modes to be selected by push buttons that illuminate when active. When any of these four are selected, the others are canceled.
5a	FREE RUN	When activated, the sweep is free-running without regard to trigger signals.
5b	INT	When activated, the sweep is triggered by any signal at the left edge of the display with an amplitude of 1.0 divisions of the graticule or more.
5c	LINE	When activated, a sample of the ac power line voltage is used to trigger the sweep.
5d	EXT	When selected, the sweep is triggered by an external signal (applied through the back panel IN HORZ/TRIG connector) between a minimum and maximum of 0.5 and 50 volt peak.
6	SINGLE SWEEP	This push button, plus a ready indicator (No. 7), provides the single sweep operation. When this operation is selected, one sweep is initiated after the sweep circuit has been triggered. Pushing this button does not cancel the other trigger modes. When single sweep is first selected, the present sweep is aborted, but the sweep circuit is not yet armed. An additional push is required to initially arm the sweep. The button must be pushed again to rearm the sweep circuit each time the sweep has run. To cancel single sweep, you must select one of the four trigger mode selections.
7	READY	When single sweep is selected, this indicator lights while the sweep circuit is armed and ready for a trigger signal. The indicator stays lit until the sweep is complete.
8	MANUAL SCAN	When the TIME/DIV (No. 9c) selector is in the MNL position, this control will manually vary the CRT beam across the full horizontal axis of the display.
9	TIME/DIV	Is used to select sweep rates from 5 msec/div to 20 msec/div. This switch also selects AUTO, EXT, and MNL modes.
9a	AUTO	In this position, the sweep rate is selected by the microcomputer to maintain a calibrated display for any FREQ SPAN/DIV, RESOLUTION, and VIDEO FILTER combination.
9b	EXT	When selected, this control allows an external input source to be used with the sweep rates.
9c	MNL	When selected, this control is used in conjunction with No. 8 (see MANUAL SCAN, No. 8).
10	FREQUENCY	This control is manually turned to allow you to tune to the center frequency.
11	FREQUENCY RANGE (band)	These two push buttons are used to shift the center frequency up or down. Frequency range on the band is displayed on the CRT readout.
12	F	This control is used for measuring the frequency difference between signals. When selected, the frequency readout goes to zero. It will then read out the deviation from this reference to the next frequency desired as the FREQUENCY knob is adjusted.
13	CAL	When this is activated, the frequency readout can be calibrated to center the center frequency by adjusting the FREQUENCY control for the correct reading. When accomplished, you should deactivate the CAL mode.
14	DEGAUSS	When this button is pressed, current through the local oscillator system is reduced to zero in order to minimize magnetism build-up around the LOs. This is done to enhance the center frequency display and amplitude accuracy. You should do this after every significant frequency change and before calibrating the center frequency.
15	IDENTIFY 500 kHz ONLY	The signal identify feature can become functional only when the FREQ SPAN/DIV is set to 500 kHz. When activated (button lit), true signals will change in amplitude on every sweep. Images and spurious response signals will shift horizontally or go completely off the CRT display. To ensure that the signal is changing amplitude every sweep, you should decrease the sweep rate so that each sweep can be analyzed.
16	PHASE LOCK	When this control is activated (button lit), it will reduce residual FM when narrow spans are selected. In narrow spans, the phase lock can be turned off or back on by pressing the button. Switching the PHASE LOCK off may cause the signal to shift position. In narrow spans, the signal could shift off the display; however, it will usually return to its phase locked position after a few moments. The microcomputer automatically selects PHASE LOCK for a span/division of 50 kHz or below in bands 1 through 3, 100 kHz or below for band 3, and 200 kHz for bands 5 and above.
17	AUTO RESOLUTION	This push button, when activated, will automatically select the bandwidth for FREQ SPAN/DIV, TIME/DIV, and VIDEO FILTER. The internal microcomputer selects the bandwidth to maintain a calibrated display. This can be checked by changing the FREQ SPAN/DIV and observing the bandwidth change on the display.
18	FREQ SPAN/DIV	This is a continuous detent control that selects the frequency span/div. The span/div currently selected is displayed on the CRT. The range of the span/div selection is dependent on the frequency band selected:
		BAND 1-3 (0-7.1 GHz) 4-5 (5.4-21GHz) 6 (18-26 GHz) 7-8 (26-60 GHz) 9 (60-90 GHz) 10 (90-140 GHz) 11 (140-220 GHz)	NARROW SPAN 10kHz/Div 50 kHz/Div 50 kHz/Div 100 kHz/Div 200 kHz/Div 500 kHz/Div 500 kHz/Div	WIDE SPAN 200MHz/Div 500 MHz/Div 1 GHz/Div 2 GHz/Div 2 GHz/Div 5 GHz/Div 10 GHz/Div
		Two additional bands are provided: full band (max span) and 0 Hz span. When max span is selected, the span displayed is the full band. When zero span is selected, time/div is read out instead of span/div.
19	RESOLUTION BANDWIDTH	This is also a continuous detent control that selects the resolution bandwidth. The bandwidth is shown on the CRT display. The range of adjustment is from 1 kHz to 1 MHz in decade steps. When you change the resolution bandwidth with this control, it will deactivate the AUTO RESOLUTION.
20	VERTICAL DISPLAY	These four push buttons select the display mode. The scale factor can be seen on the CRT display.
20a	10dB/DIV	When this is activated, the dynamic range of the display is calibrated to 80 dB, with each major graticule representing 10 dB.
20b	2dB/DIV	When activated, this will increase the resolution so that each major graticule division represents 2 dB.
20c	LIN	When activated, this selects a linear display between zero volts (bottom graticule line) and the reference level (top graticule line) scaled in volts/division (see REFERENCE LEVEL, No. 23a).
20d	PULSE STRETCHER	When selected, this increases the fall time of the pulse signals so that very narrow pulses in a line spectrum display can be observed.
21	VIDEO FILTER	One of two (NARROW OR WIDE) filters can be activated to reduce video bandwidth and high-frequency components for display noise averaging. The narrow filter is approximately 1/300th of the selected resolution bandwidth with the wide filter being 1/30th the bandwidth. Activating either one will cancel the other. To disable, completely switch filter off.
22	DIGITAL STORAGE	Five push buttons and ON control operate the digital storage functions. With none of the push buttons activated, the display will not be stored.
22a	VIEW A, VIEW B	When either or both of these push buttons are selected, the push button illuminates, and the contents of memory A and/or memory B are displayed. With Save A mode off, data in a memory is interlaced with data from B memory.
22b	B-SAVE A	When activated, the differential (arithmetic difference) of data in B memory and the saved data in memory A are displayed. SAVE A mode is activated and SAVE A button will be lit.
22c	MAX HOLD	When activated, the digital storage memory retains the maximum signal amplitude at each memory location. This permits visual monitoring of signal frequency and amplitude at each memory location over an indefinite period of time. This feature is used to measure drift, stability, and record peak amplitude.
22d	PEAK/AVERAGE	This control selects the amplitude at which the vertical display is either peak detected or averaged. Video signals above the level set by the control (shown by a horizontal line or cursor) are peak detected and stored while video signals below the cursor are digitally averaged and stored.
23	MIN RF ATTEN	This control is used to set the minimum amount of RF attenuation. Changing RF LEVEL will not decrease RF attenuation below that set by the MIN RF ATTEN selector.
23a	REFERENCE LEVEL	This is a continuous control that requests the microcomputer to change the reference level one step for each detent. In the 10 dB/DIV vertical-display mode, the steps are 1 dB or 0.25 dB if the FINE mode (No. 26) is selected.
23b	MIN RF ATTEN DB	This selects the lowest value of attenuation allowed: Actual RF attenuation is set by the microcomputer according to the logarithm selected by the MIN NOISE/MIN DISTORTION (No. 27) button. If RF attenuation is increased by changing MIN RF ATTEN, the microcomputer automatically changes IF gain to maintain the current reference level.
24	UNCAL	This indicator lights when the display amplitude is no longer calibrated (selecting a sweep rate that is not compatible with the frequency span/div and resolution bandwidth).
25	LOG and AMPL CAL	These adjustments calibrate the dynamic range of the display. The LOG calibrates any logarithm gain dB/Div, and the AMPL calibrates the reference level of the top graticule line at the top of the display.
26	FINE	When activated, the REFERENCE LEVEL (No. 23a) switches in 1 dB increments for 10 dB/Div display mode, 0.25 dB for 2 dB/Div, and volt1 dB for LIN display mode.
27	MIN NOISE/MIN DISTORTION	This selects one of two logarithms used to control attenuator and IF gain. MIN NOISE (button illuminated) reduces the noise level by reducing attenuation and IF gain 10 dB. MIN DISTORTION (button not illuminated) reduces distortion to its minimum. To observe any changes, the RF attenuation displayed on the CRT readout must be 10 dB higher than that set by the MIN RF ATTEN selector.
28	POWER	This is a pull switch that turns power on when extended.
29	RF INPUT	This is a 50 ohm coaxial input jack used to input signals of 21 GHz or below. The maximum nondestructive input signal level that can be applied to this input is +13 dBm or 30 mW. Signals above 10 dB may cause signal compression.
30	POSITION	These controls are used to position the display on the horizontal and vertical axes.
31	CAL OUT	This is an output jack that has a calibrated 20 dBm 100 MHz signal, with frequency markers spaced 100 MHz apart. The calibrated 100 MHz marker is used as a reference for calibrating the reference level and log scale. The combination of 100 MHz markers is used to check span and frequency readout accuracy.
32	OUTPUT 1ST AND 2ND LO	These jacks provide access to the output of the respective LOs. The jacks must have 50 ohm terminators installed when not connected to an external device.
33	EXTERNAL MIXER	When the EXTERNAL MIXER button is activated, bias is provided out the EXTERNAL MIXER port for external waveguide mixers. The IF output from the EXTERNAL MIXER is then applied through the EXTERNAL MIXER port to the second converter for use.
34	PEAKING	This control varies the mixer bias for external mixers in the EXTERNAL MIXER mode. This control should be adjusted for maximum signal amplitude.