Question

which instrument is used for communicating with mom?

Answer 1

ANTENNA IS USED FOR COMMUNICATING WITH MOM

Answer 2

The electronic instrument is called a transponder.  This fixed in the MOM (and on satellites and spacecrafts in space). 

An antenna array (of planar metallic hollow rods or of dish shaped or parabolic shaped Reflector)  receives electronic signals and generates a potential difference in a circuit connected to it.   A TWT (travelling wave tube) amplifier multiplies that voltage value corresponding to the signal received.

A transponder receives that amplified signal and decodes the data and processes it.  Then the reply is sent by encoding it and by directing the microwaves towards the space center on Earth using the high gain reflector on the MOM.