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Operating basics

The integer val

ues indicate the actual tuning control word. The allowed range of

the tuning control word is 0 to 4,194,304. The ﬁrst number is the current value of

the word and the second number is the target value for the tuning control loop.

In most cases, these two values are the same. However, in the case where the

TG8000 system needs to make a large frequency change to achieve signal lock,

then depending on the instrument mode, the value may slew slowly to the target

value to sta

y inside the allowed slew rate for reference systems. In this c ase, the

ﬁrst number will slew over seconds or minutes until it equals the value of the

second number. If the instrument is taking a long time to lock to an external

reference signal, the Tune readout may provide valuable information about what

is happening.

CAL. Disp

lays the tuning control word for the calibrated frequency of the

mainframe oscillator and how far the TG8000 system is deviating from the

calibrated frequency to achieve a lock to the internal reference.

The ﬁrst part of the CAL readout indicates the fractional a mount of d eviation

from the calibrated frequency. For example, a readout of “0.59e-6” indicates

a fractional correction of 0.59 parts per million. When a calibration of the

instrument oscillator is performed, the CAL readout values will typically change.

Over the life of the oscillator oven, the expected frequency drift is ±2.5 e -6, so

this

number should always be in this range. If the fractional number is not within

this range, then the instrument may have been miscalibrated, or the oscillator oven

may have drifted out of speciﬁcation since the last calibration. In this case, you

should consider calibrating the internal frequency of the instrument. This can be

performed while the instrument is in s ervice with no disruption to the operation.

(See page 2-47, CAL OVEN submenu (GPS7 module only).)

PLL. Displays the frequency in MHz and the lock status for each of the mainframe

clocks used to drive the video outputs. All of the clocks should show a status of

locked (LK) during normal instrument operation.

TEMP. Displays the current temperatures of the mainframe and CPU in °C

followed by their status. OK is displayed as the status when a temperature is within

the operating range; WARN is displayed when a temperature is out of range.

2–44 TG8000 Multiformat Test Signal Generator User Manual

Tektronix TG8000 User Manual

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