Portsdown 2019

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The Portsdown 2019 DATV system has been designed to provide an easy way to “get on air” with Digital ATV at a relatively low cost covering all of the commonly used modes, so enabling it to be used on ATV repeaters but also for RB-TV DX working.

The 2019 Portsdown is significantly different to previous versions in that the system no longer uses the custom built Filter Modulator card which has been replaced with an off-the-shelf LimeSDR Mini. Overall the LimeSDR Mini is similar in cost to the F-M board as you no longer need an ADF4351 LO module and an LO filter PCB.

The LimeSDR Mini plugs in to the Raspberry Pi USB port, preferably via a powered USB hub and produces an RF output from ~ 30MHz to 3.5GHz.

This guide is in a number of sections which cover detailed descriptions for hardware and software, how to build and configure the system, some advanced features and an FAQ.

Portsdown 2018

Portsdown 2018 has been superseded by Portsdown 2019 but there is NO intention to discontinue support of the 2018 model. Portsdown 2019 is recommended for all new builds but if you would still like an F-M board, we suggest you post on the wanted section of the forum - https://forum.batc.org.uk/viewforum.php?f=14 - or blank PCBs for home construction are still available here - BATC shop item 10.

All the wiki information on Portsdown 2018 is still available here.

Specification

The Portsdown 2019 will accept video input from a composite video source, the Pi camera, some WebCams or integrated stored test cards. It will then encode these as MPEG-2 or H264 with stereo audio.

  • Frequency range - Using a LimeSDR Mini it will transmit DATV on frequencies between 30 MHz and 3.5 GHz.
  • Power output - Typical power output varies with frequency and is plotted here: LimeSDR_Mini_Output_Power_Levels. The power output level can be increased and leveled off the frequency range by using a Portsdown 8 way RF switch on the output.
  • Transmission modes - DVB-S and DVB-S2 modes are available from the LimeSDR Mini, with QPSK, 8PSK, 16APSK and 32APSK.
  • Symbol rate - Due to the limited processing power and USB capability of the Rpi, symbol rates are generally limited to 1Ms and below (down to 66 KS), but some H264 modes will work at 2MS. Note the LimeSDR Mini hardware is capable of higher symbol rates when used with DATVExpress software.

Hardware System Diagram

Here is the latest system diagram. Note that only one of the displays is required; either the 3.5 inch or 7 inch; the digital variable attenuator is only required if you want fine (<3 dB steps) control over your PA drive levels. The Lime Gain control on the Portsdown can be used to set the coarse output level.

20190120 Portsdown 2019 Block.jpg

Building the system

The Portsdown 2019 uses the majority of the 2018 Portsdown hardware.

Portsdown 2019 Software

The Portsdown 2019 uses the same software as later versions of the Portsdown 2018 system which is known as Portsdown 2018/2019 and is based on the Raspberry Pi's Raspbian Stretch operating system.

Initially configuring the system

Once you have completed your hardware build or have bought the RPi, display and LimeSDR Mini and just "want to try it", connect up the hardware and insert an pre-programmed SD card into SD slot on the RPi.

Waveshare 3.5 inch and Element 14 7 inch touch screens

A new or upgraded SD Card (version 201902070 or later) will also work out of the box with the either screen and is ready to use with no initial configuration required. Connect the touchscreen (being very careful to align the pins on the Wavesahre correctly) and apply power to the RPi and the user interface menu 1 should appear.

No Touchscreen or Advanced Options

If you do not have a Waveshare 3.5 inch screen or the Element 14 7 inch screen, or you wish to enter the system advanced set-up pages you will need to do an initial setup - see this guide for more details: Initial setup 2019

Controlling the Portsdown 2019 system

Once the system is configured, you can control the Portsdown transmitter in one of 2 modes: by the use of the touchscreen or through the console using a second computer.

  • Touchscreen mode How to use your Portsdown transmitter using the Touchscreen LCD only
  • Console mode Use this mode to configure advanced settings such as WiFi or non-standard screens.
  • Changing system setup How to change Portsdown transmitter settings when in Touchscreen mode
  • QPSKRF or Ugly mode Notes on this special test mode and the limitations when using it
  • Setting up the WiFi How to set up the WiFi on the RPi3 Portsdown Transmitter

Advanced features

Portsdown 2019 is not just a DATV transmitter but has several advanced features which are or may be available in the future:

On line support / social media

There is a Portsdown area on the BATC forum where the BATC core team and wider ATV community will answer your questions and posting results of the latest builds and on air tests. https://forum.batc.org.uk/viewforum.php?f=103

Note that the BATC core team do not regularly visit Facebook pages - time is just too short to monitor everything and it's not easy to follow threads on Facebook. If you need a question answered please post on the BATC forums first.

Additional information

Filters and driver amplifiers are not part of the Portsdown project but VERY important

The Portsdown user's community including a map showing where user locations