Why do you think there is a high impedance audio signal on a telephone line?
Its a short course project. There is a high impedance (megaohms) audio signal on a telephone line while the phone is on-hook. We need to find it using an oscilloscope.
Other equipment to assist is allowed.
I have no clue what to do.
What will happen if the probe is earthed?Telephone uses current source in one direction and voltage source in other direction and thus a hybrid transformer is used.
Since current is high impedance signal terminated by line impedance, this is the one , that you may be looking for. Use differential probe method around hybrid or voice separator chip.
Then the telephone line will no longer be balanced and acts like an antenna to pickup a lot of mains hum. Aa balanced line cancels mains hum and other interference.What will happen if the probe is earthed?