GSM SIM900 shield displays ÿÿÿÿÿÿÿÿ

[mrq]

Hi I have tried to get my GSM SIM900 shield up and working but I have some problems.
I have followed the instructions and used the code to “Creating a test setup for the GPRS Shield” together with my Arduino Uno and the Arduino IDE.
The shield seems to work according to the leds, but the shield only displays the text “ÿÿÿÿÿÿÿÿ” when powering up the shield manually.
The communication seems to work because I have twice got the message “NORMAL POWER DOWN” when turning off the shield, but most of the time I only get a “ÿ” .

Do you have any idea of what’s wrong?

[jack]

This may be associated with your test environment, may also is caused by the antenna, you change a place to test