TM 11-6625-3087-12
One of the outputs from the IF/audio section is compared to the first local oscillator frequency and the input
frequency is calculated. The other is a RMS voltage that is processed and the amplitude of the input signal is
calculated. These values are then sent to the front panel and shown as frequency and amplitude in the appropriate
display.
The front panel keyboard and frequency fine tune knob entries are processed in the digital section and passed to
the appropriate assembly for processing. The status of the assemblies is returned to the digital section for
corrective action or operator notification. This notification is in the form of error codes and annunciator lights
on the front panel.
The digital section contains the stored software necessary to execute the diagnostic tests and calibration cycle. A
memory is also available for store/recall of nine different front panel configurations.
The first local oscillator frequency of from 50 to 8.25 MHz is mixed with 50MHz from the frequency reference
section to produce a 0 to 32.5 MHz signal. This signal matches the tuned frequency on the front panel display.
The 0 to 32.5MHz signal is amplified and split two ways.
The first path is to the rear panel BNC connector marked Fo.
The second path is used to generate the calibration output signal of from 20KHz to 32.5MHz. When
calibration is activated, this signal goes to the input section.
When wideband mode is selected, the average broadband power present on the input signal is measured, and goes
to the digital section for display on the front panel.
The input signal is monitored for correct amplitude and if incorrect, sends an overload or underload message to
the digital section.
The first local oscillator generates a frequency of from 50MHz to 82.5MHz. This frequency is exactly 50MHz
higher than the tuned frequency displayed on the front panel. The input to the first local oscillator is a precise
10MHz and 100KHz signal from the frequency reference section.
The first part of the frequency reference section uses DC voltage to generate a stable, accurate 10MHz signal.
This signal is either:
Coupled to internal circuits using a rear panel adapter.
Not used. If not used, a stable external source of 5MHz, 3.333333MHz, 2.5MHz, 2MHz or 1MHz must be
used.
The second part of the frequency reference section generates a 5MHz signal. This 50 MHz is divided and
amplified to generate the required operating frequencies of 50MHz, 10MHZ, 2MHz, 1MHz and 100KHz. These
signals are then used in various internal operations of the Level Meter.
The impairments uses the single sideband demodulated output from the IF/audio section. A DC phase jitter
output is generated and passed to the digital section for display on the front panel. An AC phase jitter output is
provided on the rear panel.
When C-message 3100Hz is selected, the single sideband demodulated audio is applied to a weighted filter to
measure noise.
When NOISE/TONE is selected, the single sideband demodulated audio is applied to a notch filter to remove the
1004Hz tone.
When all other modes, except impulse, are selected, the single sideband demodulated audio bypasses the filters.
When IMPULSE is selected, the single sideband demodulated audio is passed to the weighted filter, if selected
and then to the notch filter. The noise is then compared to the threshold level set by the operator. Any impulse
noise spike that exceeds the threshold level is counted and passed to the digital section for display on the front
panel.
1-7
Previous Page
