SystemState.PhoneSignalStrength never changes! (C#/WindowsMobile)

Question

Hi,

I'm using Microsoft.WindowsMobile.Status.SystemState.PhoneSignalStrength to get current signal strength.

But the value never changes. It only changes when phone turns on/off. I'm sure that signal is changing, 'cos taskbar shows little variantions (bars).

This piece of code has been running for hours straigth, but phonesignal_Changed only fires when I turn phone on/off. Am I doing something wrong? (C# / WindowMoblie6.1 / .NETCF2)

public partial class Form1 : Form
{
        private Microsoft.WindowsMobile.Status.SystemState phonesignal = new Microsoft.WindowsMobile.Status.SystemState(Microsoft.WindowsMobile.Status.SystemProperty.PhoneSignalStrength);

        public Form1()
        {
            InitializeComponent();

            phonesignal.Changed += new Microsoft.WindowsMobile.Status.ChangeEventHandler(phonesignal_Changed);
        }

        void phonesignal_Changed(object sender, Microsoft.WindowsMobile.Status.ChangeEventArgs args)
        {
            textBox1.Text += DateTime.Now.ToString("HH:mm:ss") + " - Signal: " + args.NewValue.ToString() + "\r\n";
        }
}

Thanks in advance. (and please forgive my poor english)

PS: I've tested in different devices (Motorolla A3100, etc...) and all have same behavior.