- Will the 50Hz mains signal interfere with the GSM Reception??
HN: It will not interfere - if you do your job right. Any laptop with embeded GSM modem inside I know is working fine. The world is full with M2M devices close to your description.
- Will the 12V PWM Fan interfere with GSM reception??
HN: It will interfere for sure, but the chance on interfere based on a good shielding on your metal enclosure is less. Just make a PCB and test it with your GSM tester like listed here:
- Is it ok to place the antenna on the rear of a mild steel powder coated box
HN: Yes, if it a lambda/4 or lambda/2 wave stubby antenna.
- Is it ok that the antenna cant see over the top of the box or will i lose all signal coming from that direction??
HN: ??? Sorry but I do not understand the question. A lambda/4 or lambda/2 will radiate omnidirectional as long you to not cover it by metal in the near. The radiation pattern of your antenna you will find in your data sheet.