Hi,
> We are thinking to buy close field probe set. Are they reliable?
> Can i measure improvements in design before send the product to the lab?
They give you an estimate of the Electric field at 3 m.
You will also need an EMI receiver.
> Can i use it in open field (3m-10m)?
Yes, absolutely. In this case, you will need an Open Site Area of 10 meters.
The steps are:
1) The EMI receiver measures the Electric Field in the environment with your device off,
at any polarization and height of the receiving antenna (read the norm).
2) Turn on the device and repeat the measures.
3) Program the EMI receiver to substract the environmental Electric Field from the Field radiated by your device.
In this way you can get a pretty good estimation of the Electric Field radiated by your device.
Enrico Migliore