tx atv

Description: This project was developed in collaboration with several other operators, particularly Marco IW1DGG, within a local radio club. The initial goal was to create a simple transmitter capable of providing sufficient power to excite the local ATV repeater. However, suitable designs with easily accessible components were not readily available. At that time, a transmitter utilizing SMD components and a Mitsubishi hybrid power amplifier (M67715) was on the market, but it was no longer widely available. After searching online, a simple transmitter was discovered that used only through-hole components and produced 50mW RF power. This design was presented at the ATV Meeting in Treviso in 2001 and can be found on the ARI Vittorio Veneto website (in Italian only). The original transmitter was slightly modified by adding a power amplifier stage based on a BFG35 (or BFG135), which provides approximately 0.5W output RF power, sufficient for operation through repeaters and for performing short-distance (tens of kilometers) direct QSOs. The electrical diagram of the complete modified circuit includes a video input section with an A-V mixer located in the upper-left part, an audio section in the lower-left part (around the TL081), a PLL and low power stage in the center (composed of the PIC, TSA5511, BFW91, and the first BFR96), and the power stage in the upper-right part (composed of the second BFR96 and the BFG135). The PCB designed is based on the ARI Vittorio Veneto design and features a simple two-layer board. All components are of "large size" (no SMD) except for the RF varicap diode. Some components are soldered directly on the component side, while the majority are mounted in a standard manner, using through-holes soldered on the bottom side of the board.

This transmitter project serves as an effective solution for local ATV repeater operations, leveraging a combination of widely available through-hole components and a carefully designed circuit layout. The inclusion of the BFG35 or BFG135 power amplifier stage enhances the RF output power, making it suitable for both repeater operation and direct communication over moderate distances.

The schematic design is organized into distinct functional sections, which allows for easier troubleshooting and modifications. The A-V mixer in the video input section ensures that video signals are appropriately processed before transmission. The audio section, centered around the TL081 operational amplifier, manages the audio signals, ensuring that they are properly amplified and mixed with the video signals.

The central PLL and low power stage are crucial for frequency stability and signal integrity. The use of the PIC microcontroller in this section provides programmable control over various parameters, enhancing the versatility of the transmitter. The TSA5511 is a key component for frequency synthesis, while the BFW91 and first BFR96 transistors work together to amplify the signal to a suitable level for further processing.

In the power stage, the combination of the second BFR96 and the BFG135 is optimized for maximum output power, ensuring that the transmitter can effectively interface with repeaters while maintaining a reliable signal quality over the intended distances. The two-layer PCB design simplifies assembly and reduces manufacturing costs, while the use of larger components facilitates easier handling and soldering, particularly for hobbyists and amateur radio operators.

Overall, this project exemplifies a practical approach to building a functional ATV transmitter, combining ease of assembly with effective performance characteristics, making it an excellent choice for amateur radio enthusiasts looking to engage in ATV communications.This project has been developed together with some other OMs (in particular Marco IW1DGG) in our local radio club. When we started looking at a simple transmitter providing sufficient power to exice the local ATV repeater we did not find anything simple to build and with components easy to find.

At that time there was on the market one transmitter based on SMDs components and using a Mitsubishi hybrid power amplifier (M67715) no more available almost everywhere. Looking on internet we found a simple transmitter based on through-hole mount components only and providing 50mW RF power.

It was presented at the ATV Meeting in Treviso in 2001 and you can find it here (in italian ony), on the ARI Vittorio Veneto web site. We have only slightly modified this transmitter adding a power amplifier stage based on a BFG35 (or BFG135) providing about 0.

5W output RF power, which is sufficient to operate through repeaters and to perform short distance (tens of km) direct QSOs. 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.