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.
The following is a summary of the main characteristics of the transmitter, together with a picture of that built by Bruno IK1OJP.
|Size:||171.3mm x 70.3mm|
|Power Consumption:||2W @ 13.8V|
|RF Output Power:||0.5W min. @13.8V|
|Op. Frequency:||1.2 - 1.3 GHz|
|N. Channels:||4 (programmable)
mod. available for 40 ch.
|Video Input:||PAL/NTSC @ 1Vpp|
|Audio Input:||Mono - line 1Vpp or
|Audio sub-carrier:||-15dBc @ 6.5MHz
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.
A picture of the first prototype we built is prvided here after. It gives a good idea of the complexity of the assembling.
|TX-ATV detailed description - english version (2MByte)|
|TX-ATV detailed description - italian version (2MByte)|
|TX-ATV 40 channels modification - english version (1MByte)
Detailed description of the modification and HEX file for PIC programming
|HEX file for PIC programming (4 channel version)
ch. 1240MHz, 1245MHz, 1256MHz and 1272MHz
|SW to easily modify the above listed 4 channels frequencies
If you want to modify the frequencies we choosed, you can use this simple SW.
It modifies the HEX file that you can use to re-program the PIC.
In order to simplify the assembly of this TX, we have procured a certain number of PCBs from a local firm (they are plated on both side with plated
holes to ease soldering) and we have prepared some kits, including all needed components.
We have still few kits available and we have also some PCBs without components (if you can procure them).
You can contact me at my e-mail address (see main page) or my Radio Club (www.aribra.it) for further information or to check for kit/PCBs availability and costs.