Data Interface

Description of Data Interface

The
audio jack is one of the interfaces on mobile devices
and tablets, it's mostly used to play music ,but it can also
be used to receive and decode data.
It can not be connected directly to a receiver, this can damage the receiver/scanner.
A simple circuit is needed to connect a receiver to this
audio jack.
( phone/tablet mic-in).
If POCSAG is decoded most often the unfiltered audio from the
receiver is used (discriminator-output). Some scanners have a discriminator output build in ,but most don't. So if you don't want to crack open your brand new receiver and do
some soldering you can try the amplitude decoding mode
which uses the earphone output from your receiver or scanner.
The receivers amplifier has an analogue filter at its output
causing distortion,it seems that the signal collapses
or rises after one bit high or one bit low,this is why it's
so hard to decode with the earphone signal, also each
type receiver has different filters and amplifier so
a standard setting is almost impossible
Another problem is the different specs of the MIC-in circuit
from the different manufacturers of android devices which
results in different amplitude levels when using the same
receiver but different devices.
So after all this how can the right audio level be found.
Well it's been tried with this app with the interface circuit.
This app is a test version there are still some errors in
it, it is used to test if the circuit works on the different devices
but it can decode the POCSAG protocol Function 3 alpha-numeric
most of the time ,however it will not work on some devices.