[General] “I have a question regarding the coexistence of your 900MHzISM radios such as RC1081 with GSM. A GSM transmitter emits 33 dBm but your maximum allowed input power is 10 dBm. Does this translate into the rather demanding requirement of minimum 23dB antenna isolation? What is the effect of having above 10dBm fed into transceiver, will the receiver only be temporarily saturated or is there a risk of permanent damage. What is the maximum allowed level to avoid permanent damage. A second question regarding interferers. As I read your datasheet a blocking interferer can be allowed to be -106dBm+3(level above sensitivity limit)+75(stated typ interferer rejection)=-28dBm. Am I interpretating your figures correctly? “

“The saturation number will not damage the module, but if the received signal is stronger than the saturated value, the incoming signal will be distorted and the module are unable to demodulate properly. This applies for the receiving channel, but for other frequency jammers (like the GSM mobile) you should look at the Blocking number that informs you about how much stronger a jammer can be at a given offset and still be able to receive at your wanted channel. As specified in the data sheet we complies with EN3001-489, which defines max values for EMC radiation from the Module, and max EMC immunity from other jammers.

A GSM-900 mobile handset transmit to the base station in the band 890-915 MHz, and the max output power is 2W. The 2 watt output power is only valid if you have extremely weak reception from the base station, and normally the output power from the mobile is much lower to save battery. The GSM system use TDMA and each GSM channel is divided into 8 timeslots. One timeslot (4.6 ms) for each mobile in traffic. The likelihood of being jammed by a cell phone is for this reason minimal. You will need weak signal from the GSM Base station, and a mobile phone in traffic (call), and place the mobile almost side by side of your antenna. Then you may see that you lose communication if you are close to the sensitivity limit of the module. We have measured this in our lab, but and are unable to jam the RC1081 with a mobile phone.

Your calculation is however correct and your application must always take into account that packets can be lost. Packet loss may happens independent of GMS-900 jammers since you are operation in a license free band where you have no control of signals from other systems.

Last Update: September 14, 2017  

September 14, 2017   523    General FAQ