The harmonic of transmitter in the wifi system

[Jameslu]

Hi all

why the 2nd/3rd harmonic of DSSS modulation is highest than QAM modulation in the same channel?

i think that is cause to different modulation, Is it correct or not?

many thanks

 

[biff44]

What exactly is the type of modulation in the DSSS?

the amount of "power" contained in a broad bandwith can "appear" to be different when viewed on a spectrum analyzer set to a narrow resolution bandwidth. For instance, FSK is a contant envelope signal and can appear to be bigger than QAM if captured in a small resolution bandwith. therefore the 2nd/3rd harmonic will also appear to be bigger than that caused by QAM.

Also, the 2nd harmonic is at twice the frequency, so its power/hz will drop by 3 dB, and more so with the 3rd harmonic.

 

[Jameslu]

thank your reply and remind to me

as your mentioned, if i will test the harmonic for DSSS and QAM of modulation, the spectrum analyzer need to set the same conditions (resolution bandwidth or video bandwidth..etc) and get the similar results.

thanks

 

[biff44]

if I am measuring harmonics in a modulated system, I crank up the RBW as big as it can get. Even then it might not be big enough.