using unitrunker with APCO 25

[briconellis]

i have a BC796D with a disc tap, but i can't pick up the signal coming from the APCO 25 system i am tuning into. i heard that i would need an amp of some kind to boost the signal and eliminate the noise in the line. My question is; what kind of amp do i need and where would i get one, or how do i make one.

thanks

Brian

 

[fmon]

Brian,

Are you running the line to the mike in jack?

 

[briconellis]

yes, from the disc tap to mic in on my laptop.

 

[fmon]

Does the tap work with other decoding programs, IE, Trunker or Etrunker?

 

[briconellis]

the tap works with all decoders. it works with unitrunker too, just not on APCO 25 control channels.

 

[funkytones]

did you choose to invert the signal? i was pumped with i first started with my 796 and the discrim tap that it took me a few extra minutes to get to that option..lol... and walla

 

[SCPD]

i heard that i would need an amp of some kind to boost the signal and eliminate the noise in the line.

It's not to boost the signal. It's to prevent the extra load caused by the microphone or line input from distorting the weak discriminator audio signal.

My question is; what kind of amp do i need and where would i get one, or how do i make one.

A single op-amp with high impedance inputs wired as a voltage follower with work. You don't need any gain unless your radio's signal is very low (some radios are). I suggest you go to a hobby electronics store and purchase a hi-Z microphone preamplifier - either pre-built or as a kit.

You also need to download an oscilloscope program to display the signal. Search this forum for examples of what a good signal looks like. If the signal is too strong (a common problem) it with clip the signal. Motorola and EDACS signals can tolerate some clipping because these are square two-level signals. You can't do that with CQPSK (P25) or FFSK (MPT1327) signals. Your sound input may allow adjusting the recording level so please check into that too.

-rick

 

[briconellis]

Thanks Rick I will try all of the above.

Brian