Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Spectrum Analyzer vs. Network Analyzer

  1. Oct 15, 2004 #1
    Hi all,

    I was wondering if someone could clarify what the difference is between a spectrum analyzer and a network analyzer.


  2. jcsd
  3. Oct 15, 2004 #2


    User Avatar
    Science Advisor
    Homework Helper

    A spectrum analyzer breaks down a signal into its various frequency components and shows the strength of each component. A pure sine wave will only show a single peak while a distorted/modulated sine wave will show a number of sub peaks.

    Network analyzer seems to be a more nebulous term and varies from simple signal/no signal to the ability to check for 'ghost' packets (ie bad termination causes unwanted reflections) With known propagation delay of cabling it can also tell the distance to the problem such as crushed or cut cable.
  4. Oct 15, 2004 #3
    A vector network analyzer will tell you reflection and transmission coefficients in both directions on a 2 port system. It will also show phase and delay differences between the ports. Both will do their thang over some frequency (or time) range.
  5. Aug 23, 2006 #4
  6. Aug 24, 2006 #5
    A spectrum analyzer is a receiver that scans all frequencies within its range, much like a scanner does.

    It then displays the peaks and valleys of a signal during it's frequency sweep.

    A network analyzer is a transmitter and a receiver built in one box, which are outputed as coax connections on the front panel, usally N connectors are used.

    If you connect the network analyzer through a filter or amplifier, it will show it's frequency response, and calculate numerous parameters of your circuit at hand such as S, Z, Y, h paramers, smith chart and polar plots, phase, group delays, and even inverse fourier transforms which will show you the time domain much like an oscillscope does.

    One of the best in the world are made by Agilent, former HP. They are god in the RF community with max frequency ranges up to 325 GHz
  7. Dec 3, 2009 #6
    Still I am confused that how a spectrum analyzer break down a signal into various frequency Components.
  8. Dec 3, 2009 #7


    User Avatar

    Staff: Mentor

    (This thread is over 3 years old....)

    Here's a tutorial for you:

    http://www.spectrum-analyzer.info/Spectrum_Intro.aspx [Broken]

    Last edited by a moderator: May 4, 2017
  9. Dec 3, 2009 #8
    (wow can't believe it was that long - time goes by so fast)

    Basically a spectrum analyzer works just like a radio receiver but with a wider tuning range, and tunes everything automatically.

    The key is heterodyning or mixing, which is a process of converting a frequency of a signal to a higher or a lower frequency. To make a mixer work, you need to introduce another signal of some frequency, which is going to be either added or subtracted to the frequency of the incoming signal. Then filter the output which is held constant.

    VCO (voltage controlled oscillator) is a circuit that changes frequency with a changing voltage. In the older radios, the VCO was tuned manually with a knob which was actually changing a voltage level on the VCO (in modern radios there is a synthesizer which does this digitally). In spectrum analyzers, the VCO is swept linearly with a ramp voltage and synchronized with the screen - and that gives you the x-axis on graph. To get the y-axis the incoming signal could be up-converted to a higher frequency by adding frequency of the incoming signal to the frequency of the VCO and filtering it out, amplifying and recovering amplitude with a diode....

    This is just a basic overview, most spectrum analyzers will have more than 4 mixing stages, gazillion of oscillators, and synthesizers, and filters - that are designed to manipulate the incoming signal by changing its frequency, amplitude, and phase.

    http://img706.imageshack.us/img706/8835/48987296.png [Broken]
    Last edited by a moderator: May 4, 2017
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook