Controlling a DATVExpress

Work is ongoing to introduce the capability to control a DATV Express exciter board from a Portsdown transmitter system without the filter modulator card. The capability will be included in the core build once it is robust. In preparation, here are some details.

The Portsdown Software running on an RPi 3 will control a DATV Express board directly via the USB port, without the need for any PC or other computer. There are some limitations on functionality, due to the state of development of the DATV Express server software, and also limitations in the RPi 3 hardware and Portsdown software. This will give a compact touchscreen interface to DATVexpress but you cannot expect the full functionality that you would get using a Windows PC to control DATV Express.

Equipment Required

For a usable Portsdown and DATV Express transmitter, you will need a Raspberry Pi 3, a Waveshare touchscreen, a DATV Express board, suitable power supplies, and transmitter filters and linear amplifiers. Connect the DATV Express to the RPi 3 using a USB lead.

Capability

Using the touchscreen, the following capabilities can be controlled:

DVB-S H264 transmissions using the Pi Camera at Symbol Rates from 333 KS to 4 MS.

DVB-S MPEG-2 transmissions using the Pi Camera at Symbol Rates from 333 KS to 4 MS.

Carrier transmission.

Successful encoding from the Pi Camera has been demonstrated between 250 KS and 8 MS, but these symbol rates are only selectable from the Console interface.

The FileTS (playing a pre-recorded TS file) and PATERNAUDIO (test card) and Desktop modes do not function properly. Work is ongoing to improve this capability. Analogue Capture does work with some EasyCap dongles, but not with others. I have seen successful encoding at between 333 and 1000 KS, with one dongle, but only intermittent pictures with another.

All FEC modes are available, and using the Console any frequency can be selected.

How it works

DATV Express Server needs to be started at least 4 seconds or so before trying to send it any content, so it is started in the following places:

- On entering the Menu (console) system with DATV Express selected as an output mode.

- In a.sh if it is not detected as running.

In both cases the system sleeps for 5 seconds while it starts up.

It is stopped (killed) whenever the Symbol Rate is changed in either the console menu or the GUI, as it needs to be re-loaded with or without the -nb parameter.

The express_server is controlled by send commands to a file /tmp/expctrl. The transmission parameters and the start transmit, or start carrier messages are sent by a.sh. a.sh is called to transmit from both the console menu, and the gui. Note that 4 band-dependent power levels can be pre-set in the Menu (Advanced Set-up).

The cease transmit or cease carrier commands are sent by the stop_transmit routines in either the menu.sh or in the gui.