Tektronix 2715 What It Does How It Works Attenuator and Low Pass Filter, 1st Converter and Bandpass Filter, 2nd Converter

Theory of Operation
2715 Spectrum Analyzer Service Manual 3-3
The Spectrum Analyzer accepts an electrical sig nal as its input and displays the
signal’sfrequency components on a CRT. Signals are applied directlyto the RF
INPUT.
The display of the input signal appears on the CRT as a graph wherethe
horizontal axis is frequencyand the vertical axis is amplitude.
The Spectrum Analyzer operates as a variable b andwidth receiver. The CRT
beam moves horizontally as arange of frequencies is scanned. When a frequency
component of an input signal is detected,the beam is deflected vertically as a
function of input power at that frequency.
There are two selections for inputs to the Spectrum Analyzer:the RF INPUT at
the front panel and the internalcalibrator signal.
The Attenuator adds attenuationto the input signal such that the level at the
input of the 1st mixer (1st Converter)is limited to no more than --30 dBm. This
would represent a full screensignal. Also, an amplifier can be inserted in the
signal path to improve sensitivity when small signalsare applied to the RF
INPUT by invoking the Preamp mode. The Microprocessor sets the amount of
attenuation, depending on the user selectedreference level, to maintain the
proper signal level.
The signal is then routed to the 1st Converterthrough a Low Pass Filter. The
Low Pass Filter attenuates out-of-bandsignals and helps minimize 1st Local
Oscillator (LO) emission at the RF INPUT. When the Preamp mode is invoked,
the Microprocessor sets the appropriateamount of attenuation, or it sets the gain
of an internal amplifier(Variable Resolution) to maintain a calibrateddisplay.
The input signal is converted to an intermediatefrequency (IF) signal of
2110 MHz. This is accomplished by mix ing the input signal with an LO signal
that varies over a rangeof 2.11 GHz to 3.91 GHz (4.26 GHz for Option 50 and
Option 75). The LO range correspondsto a range of 0 Hz to 1.8 GHz (2.15 GHz
for Option 50 and Option 75) at the RF INPUT. The output of the mixer is then
amplified to compensate forthe conversion loss, and it is filtered to allow only
the differencefrequency to pass. All other mixer products are attenuated.
The 2nd Converter down converts the2110 MHz IF signal to 110 MHz, then
routes this 2nd IF to the RF Mother board.
What It Does
How It Works
Attenuator and Low Pass
Filter
1st Converter and
Bandpass Filter
2nd Converter