Anyone using a custom built transmitter (With ordinary transistors & Ic's)....????

[muddasserniaz]

I wanted to build a FM transmitter & receiver (with FSK) for my UAV project. Although found a lot of RF products, they are either too costly or not available in my country... :p

The question is how to build a transmitter & receiver using common RF transistors and IC's... e.g. mc2833/mc33151.

Can anyone in here provide the schematics/PCB design for a FM transmitter & receiver with FSK and enough POWER +5W.

There are a lot of amateur transmitter's projects but they only support voice transmission through mic. Can i use them for data if yes.. HOW??? :confused:

The best match is this Vectronics VEC-1202K (2-meter transmitter) ... Althouh manual is available for download ... Schematic page is so dull it cannot be read. :mad:

The manual says that its a transmitter that can ...

Transmit voice, data, and more with this powerful 5-watt 2-meter transmitter! The versatile VEC-1202K 2-meter band transmitter accepts microphone input, AFSK data (up to 1200 baud) and FSK data (up to 9600 baud).

Any book/tutorial/material (for beginner level RF design) is appreciated....

Any other idea how to achieve this????

[rjet]

Are the mc2833/mc33151 modem IC's? You can do 9600 baud with any small PIC microcontroller if you know how to program them and interface it to a 5 watt transceiver. You can even build a bidirectional data radio with error correction using just a PIC and a few resistors and capacitors. You can use any voice radio, but I wouldn't suggest building your own RF circuits, because radios are so cheap and RF is tricky to work with unless you have expensive test equipment.

[muddasserniaz]

Are the mc2833/mc33151 modem IC's? You can do 9600 baud with any small PIC microcontroller if you know how to program them and interface it to a 5 watt transceiver. You can even build a bidirectional data radio with error correction using just a PIC and a few resistors and capacitors. You can use any voice radio, but I wouldn't suggest building your own RF circuits, because radios are so cheap and RF is tricky to work with unless you have expensive test equipment.


mc2833/mc13151 are Fm transmitter/receiver chips respectively from motorola.

I know how to program PICs but don't know how to interface PIC with a voice radio ..!!! any idea???

I read somewhere that using PIC can cause unnecessary RF interferance due to its internal oscillation... is that true.. :confused: ???

[rjet]

There are several ways that a PIC can be interfaced to a voice radio. The professionals like to use a FSK modem IC, but PIC's are so convenient for multi-tasking that you can usually save parts and space by using the PIC to generate the audio. I usually just use a 1K ohm resistor and a .1 uf capacitor to filter the PWM port output into a smooth FSK wave generator. The other way is a resistor ladder like the Tinytrak uses, but you need about a half dozen odd value resistors to do it. On the receiver I use another PIC, but with an op-amp to shape the input wave for a high gain zero-crossing detector.

You can connect the output of a PIC directly to the microphone input of many voice radios, but a series capacitor (~nanofarad) and a few kilo-ohms resistor voltage divider may improve modulation levels. Take a look at the tinytrak schematic and source code for examples.

I don't think the PIC generates much interference if the power and audio lines are filtered with a capacitor. Never had a problem with it yet on TX or RX.

With this design I have done half-duplex with error correction protocol at 9600 bps over a mile range with a $9 walkie talkie. One day I want to try a DDS synthesizer for higher baud rates through a video transmitter - like megabaud broadband.