Sim800c board registers only in the open space

Hi Ravi, my home designed sim800c board works well except one issue. It registers well in the open space but it takes very long time from inside the house. It never register from inside the car if windows are raised. I know it is related to signal strength. But How come none of our mobile phone has this issue. Any thing I can do to fix this? Thanks

You have some problem on antenna side. Which antenna are you using?

I have tried with spring antenna, black color stick antenna, sticker type antenna and even with a piece of wire. The result is same. If I use the sim in my mobile phone and switch it back to sim800c board it registers right away. But after some time if you restart the board it never register again.

How are you powering the module or board?

Powering with plenty of amps with spike
absorbers. Voltage is very stable at VBAT while searching the network. Actually it is a coverage issue. There is no registration issue in other locations. What confused me was mobile phones doesn’t have an issue in my locality. Anyway it works in other locations. Thanks a lot for your time.