23cm 0.5W ATV Transmitter

This page describes an audio-video transmitter for ATV in the 23cm band that we have realised and than we have also made available in an electronic kit.
The elctric diagram has been derived from the ARI Vittorio Veneto web site www.arivv.it. We have only slightly modified it and we have added a PA stage made of a BFR96 and of a BFG35 (or BFG135) able to provide about 0.5 W, following suggestions by Marcello IK1YWB and taking some ideas from the PA stages used some years ago in the Packet Radio RTX in 23 cm designed by Matjaz Vidmar.
These are the main characteristics of the transmitter.

SPECIFICATION

Size:

171.3mm x 70.3mm

Power Consumption:

2W @ 13.8V

RF Power:

0.5W min. @13.8V

Op. Frequency:

1.2 - 1.3 GHz

N. of Channels:

4 (programmable)
mod. available for 40 ch.

Video Input:

PAL/NTSC @ 1Vpp

Audio Input:

Mono - linea 1Vpp o
microf. ELECTRECT

Audio sub-carrier:

-15dBc @ 6.5MHz
50us pre-enfasi

This is the electrical diagram of the complete circuit as we modified. You can identify the video input section with the A-V mixer in the upper-left part of the diagram, the audio section in the lower-left part of the diagram (around the TL081), the PLL and low power stage in the center of the diagram (composed by the PIC, the TSA5511, the BFW91 and the first BFR96) and the power stage on the upper-right part of the diagram (composed by the second BFR96 and the BFG135).

The PCB that we have realised is based on the ARI Vittorio Veneto design and consists of a simple two layer board. All components are "big size" (no SMD) except for the RF varicap diode. Some of them have to be soldered directly on the component side, but the majority is mounted in a standard way, i.e. via through-holes soldered on the bottom side of the board.
The following picture shows the first prototype we realised. You can also fine some picture of the assembly sequence here to realize what is the complexity of the assembly of the transmitter.

Here below we have collected all information needed to assmeble the ATV transmitter kit that we have prepared (in particular the detailed assembly manual that we suggest to download).

It is also available the source code to program the PIC (in .HEX format) and a simple software for windows that allows you to modify the frequencies of the four channels within the .HEX file. The executable file has to be run in the same folder where the .HEX file is. After setting the channels, leaving the program, the file .HEX is automatically rewritten. If the frequencies shown by the SW at start-up have strange values means that the .HEX file used is not the correct one. Download the correct version from the site, or use the .HEX file contained inside the zip file together with the executable.

TX ATV 23cm 0.5W Assembly Manual v1.0 - TX-ATV-ENG.pdf (~3MB)

HEX file needed to program the PIC16F84 - TX-ATV.hex

SW to modify the channels in the HEX file - V1.2 - TxEdit.zip

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