intermodulation im3

The ACPR is usually defined as the ratio of the average power in the adjacent frequency channel (or at a specified frequency offset) to the average power in the transmitted frequency channel.
ACPR or spectral regrowth is generated by intermodulation distortion between the signal components that make up the spread-spectrum direct-sequence modulated signal.
For example in CDMA/WCDMA ACPR1 (adjacent) is 80% due to IM3 (third order) products, when ACPR2 (alternate) is 80% due to IM5 (fifth order) products.

hi V-fone
first of thanx for the info
any idea how to test ACPR in spectrum analyzer
if i take a power amplifier(say 40 Db OUTPUT) & wht will be the good ACPR ( wht level)
thanx in advance

When testing ACPR is important to take into account the power statistics of the signal. A signal with a higher peak-to-average ratio may cause more interference in the adjacent channel.
For ACPR calculation the generic formula is:
ACPR = 10 log (Padjanted/Pwanted) [dBc]
Important is the BW of the measurement, which is specified in your spec.
The limits of the ACPR are also specified in the spec. You cannot say about an ACPR level if is good or bad, if is not related to the spec limits.
The signal level at SA input shall be inside of the SFDR (spurious free dynamic range - check the SA manual for this range), otherwise the SA by self will generate intermods that will affect ACPR measurement.
These documents may help how to do the measurement:
http://www.circuitsage.com/lnapa/acprcalc.pdf
http://www.rohde-schwarz.com/www/appnotes_files.nsf/ANFileByANNoForInternet/AE07D6DCD046BD32C1256B280045851E/Sfile/1EF40_0E.pdf