OP25j

= Signal Scope =

Installation

Before running the scope app, check that the following standard pre-requisite packages are also installed: * GNU Radio * The op25 blocks * Frank's gr-fsk4 block * The op25 repeater block

The Python Numeric package is now also required. If you're running Debian or Ubuntu: {{{
apt-get install python-numeric
}}}

Other than these pre-reqs, no special setup or installation is needed.

There are three overall options or modes depending on your hardware; these are * USRP * External receiver with discriminator tap connected to sound card * External receiver with IF in the audio sound card range (e.g., 24 KHz), referred to as "audio IF"

Running with the disc-tap option

The signal scope does not require the USRP. If you have a discriminator-tapped receiver, use the "-a" option: {{{
./scope.py -a -v 25 -g 50
}}}

Running with the USRP

It's helpful to find out the current calibration error beforehand (I use kalibrate), for example, +1234 hertz: {{{
./scope.py -f 412.34e6 -RA -g 65 -c 1234 -v 25
}}}

Running in the Audio IF mode

Receivers equipped with an IF output in the sound card range can be used. This is known as "audio IF" mode.
A soundcard sampling rate of 96K is used and the IF frequency (typically 24 KHz) is given using the {{{--calibration}}} parameter:

{{{
./scope.py -A -c 24e3 -g 50 -v 25
}}}

Feature overview * Spectrum plot * Baseband oscilloscope * Eye Pattern Diagram (Datascope) display supporting several standard symbol rates * Constellation Diagrams * Demodulated Symbol Output * Correlation (including Fast Auto-Correlation) * Direct-frequency entry, signal gain and fine-tuning controls * User-selectable demodulator (FSK4 or QPSK)

In the USRP and audio-IF modes, several additional program functions are enabled (spectrum FFT, constellation diagram, PSK demod, and iDEN correlation).

In all modes, the {{{--wireshark}}} option is used to write received P25 packet data to Wireshark.

Spectrum Display

Image(a.png)

The controls arranged along the bottom of the page are: * Frequency: to retune, type the new frequency here and press ENTER * Signal Gain: adjusts the baseband (demodulated) signal level * Fine Tune: adjusts tuning frequency over +/- 3000 Hz range * Demod: Selects demodulator (currently used in Demodulated Symbols only)
Except for the signal gain control, these controls are only available in USRP RX mode.

Eye Pattern Diagrams

The scope input source can be connected either before or after the symbol filter using the Viewpoint toggle.

Also the proper speed must be selected from the available options.

Image(b.png)

Constellation Diagram

Image(c.png)

Demodulated Symbols

Image(d.png)

Correlation

Image(e.png)