Agilent Technologies 8960 10 Series Reference Manual page 507

Block Diagram
Frequency Counter The Frequency Counter is used to measure external frequencies from the front panel
Audio IN, High or Low BNC connectors, and to measure internal signals for diagnostics. The external input
can receive a signal between 20 Hz and 50 MHz, with a level from 25 mV to 8 V rms.
The counter circuit is based on the METRON IC. This IC contains a reciprocal counter. A reciprocal counter
functions by counting the input signal and a reference signal simultaneously during a selected gate period. At
the end of this period, the counting is stopped and the values of the signal and reference counters are read.
The ratio of these values is used to calculate the input signal frequency.
Audio Section
Audio Analysis Path Externally applied audio signals can be analyzed through the test set's DSP module
for such characteristics as AC level, SINAD, or distortion.
The audio signal to be analyzed is input to the test set using the front panel Audio IN High and Low
connectors. The signal is then routed to the Analog To Digital Converter module's measurement sampler for
analysis by the DSP module.
The Audio In connector accepts signals from 20 Hz to 15 KHz, at input levels from 10 mV to 20 Vpk.
Audio 1 Path The Audio 1 path provides analog baseband signals used for frequency modulation of the test
set's RF sources. Up to four separate audio sources may be summed together in any combination to provide the
composite Audio 1 output. These include the external FM input, internal direct digital synthesis (DDS,)
regenerated SAT, and audio echo input.
The external FM input accepts an externally supplied audio signal with a peak voltage between 0.25 and 2
Vpk.
The internal DDS generates low distortion audio signals from DC to 20 KHz with 0.1 Hz resolution. One to
four signals may be generated and internally summed, with independent level control of each waveform.
The SAT regeneration circuit outputs a signal which is phase-locked to a received SAT signal. This is useful
for testing situations where the test set needs to emulate a mobile station.
The audio echo input is used for retransmitting the received audio after a selectable time delay, to check both
radio transmit and receive paths simultaneously.
For most applications, only one or two of these Audio 1 path sources are enabled at any given time.
Audio 2 Path The Audio 2 path provides a secondary means for sending analog baseband signals to the FM
modulator. Audio 2 contains only one source, a DDS similar to that used for Audio 1.
Typically, the Audio 2 path DDS is used for cases where multiple signals must be summed together with the
lowest possible distortion. Another potential use of Audio 2 would be to obtain higher output levels than Audio
1 is capable of (up to twice as much), assuming the two outputs are set to the same frequency and phase, and
then summed together at the Baseband Generator module.
Audio 2 is rarely used in practice because the DDS used for Audio 2 is the same DDS that is used for the front
panel audio output.
Audio Out Path Any one of four inputs may be coupled to the front panel audio output connector. These
include a 4 channel DDS (shared with Audio 2), receiver discriminator audio from the Demodulation
Downconverter module, audio echo from the Analog To Digital Converter module, and audio vocoder.
The front panel output is capable of providing signal levels up to 9 Vpk into > 600 ohm loads, and up to 0.8 Vpk
into an 8 ohm load (e.g. speaker). The output level is calibrated for all modes except discriminator audio,
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