the difference between intermodulation and cross-modulation

[charles_lu]

cross modulation

What's the difference between intermodulation and cross-modulation, or
they are identical?
Please help me to understand these two term deeply, thanks!

 

[sergio mariotti]

cross modulation intermodulation distortion

I don'know if there is an official definition on tech. vucabularies, but...

Intermodulation is the (unwanted) generation of harmonic products of every integer order.
Calling F the frequency, are IM products F1-F2, 2F1-F2, 2F1, 3F1-2F2 etc. The order is the sum of the absolute multipling factors.

Cross-modulation is a particulal case of intermodulation fenomena and is related to the difference between 2 signals, and apply to the demodulated signals. The tipical case is when you want receive a modulated signal (i.e. FM radio) and an amateur radio close to you transmit high power AM modulated voice, you'll receive a cross-modulated signal, a mixture of wanted and unwanted demodulated signal

 

[RFDave]

cross modulation distortion

Here is the definition that I'm familiar with: Cross Modulation is a full duplex radio specific impairment. In other words, GSM handset's don't suffer from this. In CDMA handsets, it occurs primarily in the LNA. Here, TX leakage, (which is modulated) mixes with a strong off channel interferer in the LNA. Due to 3rd order distortion, some of the TX modulation is transferred to the Interferer. IS-98C STD 9.4.2 requires this Interferer to be +/- 900kHz and+/-1.25 MHz away from the desired. This means that some of this transferred modulation (cross mod) will spread into the 1.23 MHz desired signal band, corrupting it. Adequate TX filtering or high LNA IP3 are the ways to combat this problem. I've attached a paper from Microwave journal that covers this.

Dave