transreceiver

[zb10948]

hi everyone. i am new to this forums, and i already have some questions for my project. i would like to build a audio transreceiver. it has to be able to operate on a distance of ~ 150 meters, and the optical visibility isn't full. i would like to talk with someone in same building, from balcony to balcony (same side of building), so signal could encouter a number of walls.

i figured that most of cheap transreceivers are operating on FM band. however, hundreds of people could hear me on their radios, so i tought i could use digital signal. the idea was to use ADC in transmitter circuit to convert the signal to digital values, then use a multiplexer for parallel to serial convertion. the receiver would have a demultiplexer hooked on to a DAC. altogether with an signal amplifier.

in essence, analog signal would be converted with ADC that has enough resolution to provide decent sound quality. ADC's eight digital outputs are hooked directly to multiplexer's eight information inputs. if ADC's oscillator is working on 12 KHz, i would need a code word generator that shuffles trough all code words for multiplexer's input ports(000, 001, 010, 011, 100...), and that works on frequency of 96KHz (12x8). generator would be connected on mux's address inputs(n = 3 for 8 information inputs). that kind of signal would be amplified then transmitted. receiver uses reverse procedure.

my questions are :

- do i need to use any pre-filtering before the signal from the microfone reaches ADC's input? and any analog post-processing needed after receiver transforms digital to analog?

- i can design and implement all the digital components. can someone point me to some nice RF transmitter / receiver circuit that's suitable for this project?

- what kind of amplifier can i use before digital signal is transmitted? i'd like device portable, so what's with antenna?

and of course, any other stuff regarding this project. if someone thinks i'am mad for trying to make a shortrange digital transceiver, please post your opinions on how i could realize this project. bear in mind transmission distance, quality, and of course, component prices.

thank you in advance!



   

[Shahriar]

Dear zb10948

I also plan to do the same project and i am trying to build my own transceiver.

1- you'd better to use an AVR MCU for ADC conversion. because  micro will give you more flexibity in your project. for example If several people are talking to each other, you can allow someone to hear you or not and many other abilities.

2- The most important thing with transivers is STABILITY. The easiest way for you is to buy a TLP434/RLP 434 (Transceiver, receiver). because they use SAW resonator and have nice stability. but the problem with them is low baude rate. typical baude rate for them is 4800bps.the max rate is 200,000bps. there are some othere modules with higher power and more data transfer baud rate. Look for them in your area.

3-for TLP434 the typical input is Vcc. I mean the data amplitude  should be equal to the Vcc of transmitter. Because they are workong at 434MHZ the antena is very small. (approximately 18cm for TX) so you do not need any special amplifier just a transistor for switching if The Vcc of your ADC and your TLP differs

HTH - Shahriar