OP25j

= Signal Scope =

Installation

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

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

There are two overall options depending on your hardware (USRP or disc-tap).

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
}}}

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
}}}

In USRP mode, several additional program functions are enabled (spectrum FFT, constellation diagram, PSK demod, and iDEN correlation).

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