The Portsdown DATV transceiver system

This page is designed to give an overview of the Portsdown transmitter project - for more details and an FAQ see the user guide. For interactive discussion with other constructors see the BATC members forum:

• Portsdown Transmitter User guide
• The Portsdown Receiver
• BATC members forum pages

Introduction

The Portsdown DATV transmitter project provides an easy way to “get on air” with Digital ATV at a relatively low cost, covers most of the common modes and involves some basic construction.

• Symbol rates to include the Reduced Bandwidth (RB-TV) modes and “normal” DATV modes

• Frequency coverage of 146 MHz, 437 Mhz and 23cms

• Cost-effective stand-alone (not PC based) Digital TV Transmit solution

• Analogue video input to allow use of camcorders and mixing desks

• Use of commonly available components and modules

• Modular construction enabling a step-by-step system build and easy trouble shooting

• Designed to encourage home construction and requiring an average skill level

• Fully documented and supported including easy software installation and upgrades

The aim is to enable an amateur operator with little or no knowledge of Digital ATV to construct the hardware elements, load and configure the software and use the system to send live Digital ATV signals across town on his existing aerials. It will include the new DX RB-TV modes and the ability to receive and transmit to local repeaters using the more traditional 2 and 4 Msymbol DATV modes.

Block Diagram

System description

At the heart of the Portsdown project transmitter is a Raspberry Pi (RPi) computer running a BATC customised version of the F5OEO rpidatv software. The choice of the RPi is primarily due to the fact that it has an on-board MPEG-4 (H264) encoder and the versatile hardware interface (GPIO) capabilities.

A touch screen interface (available from Amazon) on the RPi enables the system to be used without further need to connect up keyboard and mouse. If the LCD is not available, the system can be controlled by using an external PC connected over a wired or wi-fi network (console mode).

The output from the Rpi is connected to the Filter Modulator board (the only custom piece of hardware - PCBs will be available from the BATC shop). This board also requires an on frequency local oscillator signal and the Portsdown transmitter software has been designed to control an ADF4351 chip (available from ebay) to give an output on 146, 437 and 23cms.

The Portsdown RPi software is capable of controlling the ADF4351 Local Oscillator module to give outputs on 146 MHz, 437MHz and 23cms.