Controlling a DATVExpress
Software versions 201702060 and later include the additional capability to control a DATV Express exciter board from a Portsdown transmitter system without the filter modulator card. Here are the full 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. The system gives a compact touchscreen interface to DATV Express 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 125 KS to 4 MS.
DVB-S MPEG-2 transmissions using the Pi Camera at Symbol Rates from 125 KS to 4 MS.
Carrier transmission.
Successful encoding from the Pi Camera has been demonstrated between 125 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.
The output level can be set independently for each band from Advanced Settings, option 5. The power level calibration (0 - 47) is very close that that set in the Windows V1.23 DATV Express software.
Warnings and Limitations
- The DATV Express board should connected to the RPi and powered on before the RPi is booted.
- With an SR of 1000 KS selected, there are spurious emissions about 35 dB below the main transmission at plus and minus 6 MHz. Other SRs do not seem to be so badly affected.
- The Portsdown capability of booting straight to transmit is not available with the DATV Express board.
- The PTT pins on the DATV Express board that are activated in the Windows version of DATV Express are inactive in this version. The PTT and band select lines on the Portsdown transmitter are functional as normal.
- There is a delay of 5 seconds before the first transmission after switch-on and after any change of SR. This delay is to allow the DATV Express firmware to be downloaded from the RPi.
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 the DATV Express server application 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 sending 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.
Thanks to Chris MW0LLK for his help in delivering this capability.