Portsdown 4

The Portsdown 4 transceiver software has been specifically designed to be used with the Raspberry Pi 4 and the official Raspberry Pi 7 inch touchscreen. It will drive a Pluto SDR or the LimeSDR.

Portsdown 4 is the simplest and easiest to construct, with a barebones system consisting of:

• Raspberry Pi4 2GB model
• 7" touch screen
• 8, 16 or 32 GB SD card
• Adalm Pluto or Lime SDRmini SDR hardware

This will give you a DVB-S2 and DVB-T DATV transmit system from 30 to 3500 MHz when using a Lime SDR and 50MHz to 4100 MHz with the Pluto.

With the addition of a MiniTiouner USB receiver [[1]], you will have a full spec DVB-S/S2 DATV transceiver.

With the addition of the Knucker USB tuner you will also have DVB-T receive capabilities.

Building a Portsdown 4

Dave G8GKQ published this step by step guide to building a Portsdown 4 in CQ-TV 271:

media:Getting Started With Portsdown 4.pdf

Capabilities

Portsdown 4 transmit capabilities:

• DVB-S, DVB-S2 and DVB-T (H264 only) transmissions from a Pluto SDR connected by USB. More details here.
• DVB-S, DVB-S2 and DVB-T (MPEG-2 and H264) transmissions from a LimeSDR Mini or LimeSDR USB using stock LimeSDR firmware
• DVB-S and DVB-S2 (MPEG-2 and H264) transmissions from a LimeSDR Mini using "LimeDVB" firmware
• DVB-S (MPEG-2 and H264) transmissions from a DATV Express Board connected by USB
• Supported transmit video sources include the Raspberry Pi Camera, C920 WebCam or a USB-connected EasyCap composite video capture device
• Streaming to the BATC Streamer using the Raspberry Pi Camera or EasyCap composite video capture device as a source

Portsdown 4 receive capabilities:

When a MiniTiouner USB receiver is connected via USB:

• Reception and display of DVB-S and DVB-S2 (MPEG-2, H264 and H265) signals - see https://wiki.batc.org.uk/DVB-S/S2_Reception

When a BATC Knucker USB tuner is connected by USB:

• Reception and display of DVB-T and DVB-T2 (MPEG-2, H264 and H265) signals

When the Portsdown 4 is connected to the internet:

• Display of streams from the BATC Streamer

Received audio can be heard through either the Raspberry Pi AV socket or a compatible USB audio dongle.

Portsdown 4 test and alignment aids

• Control of a Pluto, LimeSDR Mini, DATV Express, ADF4351, Elcom and SLO Microwave Sources using the Portsdown 4 Signal Generator.

• Basic spectrum display of band occupancy using the "Portsdown Band Viewer" - note this requires a LimeSDR Mini to be connected.

Hardware

Only the Raspberry Pi 4 and the Official 7 inch touchscreen (or the DFRobot DFR0550 5 inch touchscreen) are planned to be supported in the near future.

Portsdown 4 GPIO connections

Due to a reassignment of the GPIO pins on Raspberry Pi4, the connections are different to previous generations of Portsdown.

The Portsdown 4 GPIO Connections are defined here: Portsdown 4 GPIO Connections.

Powering the LimeSDR

The Raspberry Pi 4 has increased power capabilities on its USB ports, so it is recommended that you connect the LimeSDR directly to the Raspberry Pi. For some reason, the LimeSDR Mini sometimes works better when connected to the USB2 ports (the black ones, not the blue ones).

Powering the Pluto

The Raspberry Pi 4 has increased power capabilities on its USB ports, and the Pluto does not work well with USB Hubs, so it is recommended that you connect the Pluto directly to a USB3 port (the blue ones) on the Raspberry Pi 4. Do not use a USB hub or power the Pluto from its USB power port.

The Pluto is more reliable and less likely to drop out if fed with about 4.9v on USB. So, set the RPi input voltage to 5.0v, or use another power source to make sure that the Pluto is not fed with over 5.0v.

If powering the Pluto using the USB lead from the Pi you may have USB instability issues if the Pluto receives over 5V. As the Pi prefers voltages around 5.1-5.2V this can cause problems. One way around this is to carefully cut into the USB lead and add a Schottky diode (e.g. 1N5817) in series with the positive conductor. With a supply voltage of 5.15V to the Pi the Pluto receives 4.85V and both work correctly.

Portsdown hardware

Full details of the Portsdown hardware are available here.

Software

The Portsdown 4 software is available on a pre-programmed SD card which you can buy from the BATC shop https://batc.org.uk/shop/portsdown-transmitter-pre-programmed-sd-card/

If you wish to build your own card the build is on GitHub at https://github.com/BritishAmateurTelevisionClub/portsdown4

Langstone Narrow Band Transceiver

The Portsdown 4 software build is also compatible with the Langstone Microwave transceiver software, which can be loaded from touchscreen selections (menu 2) AFTER the Portsdown software has been installed.

See https://wiki.microwavers.org.uk/Langstone_Project for more details and the full spec of the Langstone.

Note: the Langstone software needs a Pluto SDR to be connected by USB, and a compatible USB Audio dongle.

Pluto Capabilities

The Portsdown 4 support for the Pluto SDR is still under development and there are some limitations on functionality as described here Portsdown 4 Pluto.

FAQ

• Is it possible to rotate the PiCam image in software as it is on it's side?

No - you need to do the camera mounting modification which Colin G4KLB described in CQ-TV 267

• Can I upgrade from Langstone or a previous version incluing Portsdown A27?

No - you must start with a clean image on your SD card

• When I try to update I get the error "Unable to contact GitHub for update, Internet connection to Google seems OK". The solution is to log in by ssh and run the following commands:

cd /home/pi
wget https://raw.githubusercontent.com/BritishAmateurTelevisionClub/portsdown4/master/update.sh  -O /home/pi/update.sh
chmod +x /home/pi/update.sh
./update.sh

• I have built my Portsdown 4 but the screen is upside down. How can I get it the right way up?

Menu 3, System Config, Invert 7 inch

More information

For more information and to ask any questions see https://forum.batc.org.uk/viewtopic.php?f=103&t=6804