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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.
