AVCOM PSA-65C Preliminary Operating Instructions page 13

15. VERTICAL POSITION
Controls the position of the sweep.
TO SET: With no signal present, the "REFERENCE LEVEL" switch set to 0 dBm, the SPAN
control set to 1MHz/div, and the VARSPAN control tuned to the FULL position, adjust the
sweep to be centered between the two small "tic" marks located between -60 and -70 dBm at
the bottom of the display. Do not readjust for any other reference level.
16. VERTICAL SENSITIVITY
Used to select vertical amplitude sensitivity of either 10 dBm/div or 2 dBm/div. Normally this
switch should be in the "10 dBm/div" position. The 2 dBm/div is most helpful when observing
very small signals. Readjustment of vertical position is normally required.
17. SWEEP RATE
SWEEP RATE controls the speed of the horizontal sweep across the CRT display. For
general observation, a sweep rate just fast enough that "trace flicker" disappears should
be used. For accurate amplitude measurements the sweep rate should be set to the slowest
rate. Generally, the sweep rate should not be set to the fastest rate (fully clockwise).
18 REFERENCE LEVEL dBm/dBmv
The Reference Level control establishes the amplitude calibration for the display. When set
at the 0 dBm position, with the scale switch in the 10 dB/DIV position, signals peaking at the
2nd line from the top, the -10 dBm / + 49 dBmv line, would have a strength or amplitude of -10
dBm / +49 dBmv, signals peaking at the -20 dBm / +29 dBmv line would have a signal strength
of -20 / +29 dBmv, dBm and so on.
When the Reference Level control is set to -20 dBm the very top line represents an amplitude
of -20 dBm / +29 dBmv and the second line down would be -20 dBm minus 10 or -30 dBm (+29
dBmv minus 10 equals +19 dBmv) subtract 10 for each line down to get the signal level
represented by that line.
The same is true for the -40 dBm position except that -40 dBm / +9 dBmv signals would be at
the top line. This is the most sensitive position and signals as weak as -90 dBm can be seen.
19. DIGITAL FREQUENCY LOCK
The Digital Frequency Lock (DFL) is a microprocessor function that prevents analyzer drift
and is helpful when monitoring a discrete signal. Typical lock range ±100 KHz. Lock is normally
on at start-up, push FREQ LOCK button to turn off. A flashing lock LED indicates lock circuit
is active. LED illuminated indicates frequency is locked.
20. AM-FM SELECTOR SWITCH
The AM-FM SELECTOR SWITCH activates either the AM or FM demodulator.
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