Checking CDMA Phone/Modem signal quality through Minicom

In the last two blogs, I wrote about how to use a Chinese PCMCIA Express CDMA Modem to send and recieve voice calls and SMSs using Minicom. In this blog, I will write about how to check the signal quality of the Modem/Phone through Minicom.

First a little understanding of what we are measuring. We are measuring the signal power strength in dBm. Since dBm is a logarthmithic unit, the decrease of about 3 dB implies roughly doubling of power. We typically get CDMA signal strength in the range from 0 to -104 which equates to 1.0 mW to 0.1pW. A -50 value is better than a -60 value.This is because -50 dBm comes to 10nW whereas -60 dBM comes to 1nW. A value of 105 from the modem implies that the modem is in a no service zone.

Now my Minicom output

AT+GMR will give me the software version.

AT+GMR
+GMR: S/W VER: SUC6002 Ver 1.0
OK

AT+GMM will give me the model number of the modem.

AT+GMM
+GMM: SRE 100
OK

AT+GMI will give me the manufacturer information

AT+GMI
+GMI: BELLWAVE CO. LTD.
OK

A simple Google search finds that the Bellwave Co. Ltd. is a South Korean company based in Seoul. I don't know whether the Chinese manufacturer bought the data module from Bellwave or not or they simply "copied" the module.

Now to check the signal strength. The command to check signal strength is AT$RSSI. It gives me the results in dBM.

AT$RSSI
-48
OK

Signal Strength is -48 dBM

AT$RSSI
-50
OK

Again,

AT$RSSI
-48
OK

Now I am shortening the retractable antenna. The signal quality immediately drops.

AT$RSSI
-61
OK

The antenna is completely inside the card. The signal strength is low.

AT$RSSI
-76
OK

I can now call and receive calls, send and read SMSs and check signal quality in Linux through Minicom.I don't need to boot to Vista for these functions anymore. If anybody reaches these Blogs and needs my help, leave a message.