sounds like you are inputing the frequencies for normal FM reception. What you need to do is program those frequencies in trunking mode. If you listen to a trunked system conventionally, you are not going to hear the whole conversation if you hold your scanner on one frequency.
If you don't understand trunking, here's a brief overview.
Example - there are 100 people in a room. Not all 100 people need to use the phone at the same time, so the people that own the room only put 10 phones in the room thinking that no more than 10 people are going to need to use a payphone at the same time. Someone feels the need to speek and picks up the first available phone and then when they're done, someone else uses the phone.
Now to relate it to radio - think of the payphone as a frequency and the people needing to use the payphone as a radio channel. Not all 100 channels in a trunked system are going to be used at the same so they reserve the maximum number of frequencies that may be used at the same time. When someone on channel 1 keys up, they are assigned a frequency to talk on. When they key up again, they may not get the same frequency because someone else on a different channel may have been talking on the frequency the person on channel 1 was using before.
The main reason behind trunking is so an agency with 100 channels doesn't have to reserve 100 frequencies, they can get away with reserving maybe 10-20 frequencies.
As more things are using the radio waves now more than before, available frequencies are becoming very limited and we need to reduce the number of frequencies being used.
This whole message is too long to proof read and i'm tired so i hope there are no errors
if this does not answer your question please email me.