The document discusses the components and operation of a spectrum analyzer. It describes: - Major blocks of a spectrum analyzer including the RF input, mixer, IF gain, IF filter, detector, video filter, local oscillator, sweep generator, and display. - How these blocks work together to convert an input signal to different frequencies, select specific frequencies using filters, detect the signals, and display the results on screen. - Functions of the front panel including setting frequency, amplitude, resolution bandwidth, sweep time, and input attenuation. - How spectrum analyzers can be used to analyze signals and characterize devices under test by adjusting settings like frequency and resolution bandwidth.

1. Spectrum Analyzer
Name - Vivek Kumar
Roll No- 30

2.  Advantages and disadvantages
PresentationOutline
Introduction
Types of spectrum analyzers
Front Panel
Using device under test

3. Spectrum Analyzer
• What is a Spectrum Analyzer?
A spectrum analyzer measures the magnitude of
an input signal versus frequency within the full
frequency range of the instrument
Spectrum analyzers usually display raw,
unprocessed signal information such as voltage,
power, period, wave shape, sidebands, and
frequency. They can provide you with a clear and
precise window into the frequency spectrum.

4. • Swept tuned spectrum analyzer : It sweeps across the
frequency range, displaying all the frequency
components present. This enables measurements to be
made over a large dynamic range and wide frequency
range.
• FFT based spectrum analyzer : The FFT analyzer takes a
timedomain signal, digitizes it using digital sampling,
and then applies the mathematics required to convert
it to the frequency domain. The result is displayed as a
spectrum.

5. Block diagram

6. Major blocks in a spectrum analyzer are:
1] RF input attenuator,
2] Mixer,
3] IF (Intermediate Frequency) gain,
4] IF filter,
5] Detector,
6] Video filter,
7] Local oscillator,
8] Sweep generator,
9] CRT display.

7. IF Filter
The IF filter is a bandpass filter which is used as the
window for detecting signals. It's bandwidth is also called
the Resolution bandwidth (RBW) of the analyzer and can
be changed via the front panel of the analyzer.
If resolution bandwidth is narrowed, selectivity is
improved.
This will also often improve Signal to Noise Ratio. The
optimum resolution bandwidth setting depends heavily
on the characteristics of the signals of interest.

8. Detector
The analyzer must convert the IF signal to a baseband or
video signal so it can be viewed on the instrument's
display.
Many modern spectrum analyzers have digital displays
which first digitize the video signal with an analog-to-
digital converter (ADC).
This allows for several different detector modes that
dramatically effect how the signal is displayed.

9. Video Filter
The video filter is a low-pass filter that is located after the
envelope detector and before the ADC. This filter
determines the bandwidth of the video amplifier, and is
used to average or smooth the trace seen on the screen.
The spectrum analyzer displays signal-plus-noise so that
the closer a signal is to the noise level, the more the noise
makes the signal more difficult to read. By changing the
video bandwidth (VBW) setting, we can decrease the peak-
to-peak variations of noise

10. Local Oscillator:
The local oscillator is a Voltage Controlled Oscillator (VCO)
which in effect tunes the analyzer.
The sweep generator actually tunes the LO so that its
frequency changes in proportion to the ramp voltage.
This also deflects the CRT beam horizontally across the
screen from left to right, creating the frequency domain
in the x-axis

11. RF input attenuator:
The RF input attenuator is a step attenuator
located between the input connector and
the first mixer. It is also called the RF
attenuator.
This is used to adjust the level of the signal
incident upon the first mixer.
This is important in order to prevent mixer
gain compression and distortion due to
high-level and/or broadband signals.

12. IF gain
The IF gain is located after the mixer but before the
IF, or RBW, filter. This is used to adjust the vertical
position of signals on the display without affecting
the signal level at the input mixer.
The IF gain will automatically be changed to
compensate for input attenuator changes, so signals
remain stationary on the CRT display, and the
reference level is not changed.

13. Let's see how these blocks work together to make a
spectrum analyzer.
First of all, the signal to be analyzed is connected to the input of the
spectrum analyzer.
This input signal is then combined with the LO through the mixer, to
convert (or translate) it to an intermediate frequency (IF).
These signals are then sent to the IF filter.
The output of this filter is detected, indicating the presence of a
signal component at the analyzer's tuned frequency.
The sweep generator provides synchronization between the
horizontal axis of the display (frequency) and tuning of the LO.
The resulting display shows amplitude versus frequency of spectral
components of each incoming signal.

14. Front Panel
• The three primary hard keys on any
spectrum analyzer are: frequency,
amplitude, and span
• Other important control functions
include setting the resolution-
bandwidth, sweep time, input
attenuator and video bandwidth
• Most analyzers allow you to enter
values by either punching in the value
on the number pad, or by "dialing" up
or down to the desired value using the
front panel knob

16. Source:
Set frequency to center of bandpass filter
Set amplitude high enough to see signal
clearly
Spectrum Analyzer:
Set frequency and span accordingly
Start with large RBW
Decrease RBW using arrow keys - show how
display traces shape of filter

18. There are two major instruments that are
capable of making stimulus-response
measurements. A network analyzer and
a spectrum analyzer
this is to use the spectrum analyzer’s built-in
amplitude correction function in conjunction with a
signal source and a power meter. Figure 7 depicts the
frequency response of a signal delivery network that
attenuates the DUT’s signal.

20. To cancel out unwanted effects, measure the attenuation or
gain of the signal delivery network at the troublesome
frequency points in the measurement range. Amplitude
correction takes a list of frequency and amplitude pairs,
linearly connects the points to make a correction “waveform,”
and then offsets the input signal according to these
corrections. In Figure 8, the unwanted attenuation and gain of
the signal delivery network have been eliminated from the
measurement, providing for more accurate amplitude
measurements.

22. In the modern spectrum analyzer, you can also directly
store different corrections for your antenna, cable and
other equipment so calibration will not be necessary every
time a setting is changed. One way to make more accurate
frequency measurements is to use the frequency counter
of a spectrum analyzer that eliminates many of the sources
of frequency uncertainty, such as span

23. The output of the tracking generator (source) is
connected to the input of the DUT and the response is
measured by the
analyzer (receiver).
As the analyzer sweeps, the tracking generator will
always be operating at the same frequency so the
transfer
characteristics of your device can be measured

24. Advantages :
•Able to operate over wide frequency range
•Wide bandwidth
•Not as expensive as other spectrum analyzer
technologies
Disadvantages:
•Cannot measure phase
•Cannot measure transient events
Advantages and disadvantages

25. Thank you