Originally Posted by
IFE Wizard
I will try and reply to your question.
In testing (see link in my previous message) it was noted that when telephones of different systems i.e. GSM and CDMA were in close proximity and transmitting at the same time a “third-order intermodulation” product was observed in the DME band and “fourth order” in the GPS band, with the un-wanted frequency components as high as aprox -15dBm. This signal would only exist with two or more phones transmitting at the same time.
Note:- Intermodulation products are unwanted frequency components resulting from the interaction of two or more spectral components passing through a device with non-linear behaviour. The unwanted components are related to the fundamental components by sums and differences of the fundamentals and various harmonics.
Well…..you asked.
Is this specific enough???
No. I wanted to know what specific frequencies were involved. Third order intermod occurs at the frequency 2xf
1-f
2. If f
1 and f
2 are close in frequency, then third order intermod occurs in the same band as f
1 and f
2. I didn't see how two cellphone signals could cause third order intermod in the 960-1215 MHz band. But after looking at the report you cited, I see that they had one phone set up for the US frequency band at 824 MHz and the other set up for the European band at 901.9 MHz. The report says that such an intermod occurance is very unlikely because in any location only one band or the other is used, not both. But I wonder how quad-band phones work when they are out of range of any cellular network and they search for a network. Maybe this kind of intermod could occur then.