# Confusion in sync-async transmission in RF circuit

I am learning about building an RF transmitter circuit. Now one answer in Answer to DIY RF Transmitter Circuit specified " Very first thing you have to decide on data is whether you want synchronous/asynchronous one. By which I mean the local sine wave oscillator (stage 2 above) are in phase or not."

So, my understanding of synchronous-asynchronous comes from using a clock. For example we use clock in sync-counters, so we say outputs of each flipflop is in sync with the global clock(one clock). In async-counters, we say output of each clock, in some sense, is in sync with the output of the previous block(because output of one flipflop is fed as clock into the next flipflop) and not a global clock.

Now, in above RF transmitter circuit, say my data is 1010, say I converted it into a signal like square wave where 1 becomes 5 volts and 0 becomes 0 volts and the signal has a period of 2T where T is duration for high and low in signal. I modulate it on the carrier signal generated from oscillator and I send it. When I am sending the signal then I should receive it in same order, right? Because my Left Most Bit(0) left first from transmitter side and I should receive it first at receiver side. The notion of asynchronous or synchronous does not make sense here to me.

• The answer you link is very poorly written, and your question is more based more on its flaws than in fact. While in theory it is possible to phase synchronize a transmitter's and receiver's oscillators, in practice it is not often done, has fairly limited use, and not something you need to worry about as a beginner to the concepts. Basically your question reflects little more than the problems with the post you link to. Oct 10, 2020 at 15:23
• What is true is that when you receive a modulation pattern over a radio link, you typically need some sort of synchronization mechanism to "find" the bits or symbols. Typical packet-oriented radio chips with an SPI or similar interface have an internal functional block that does this. With more primitive ones you have to do so in your own software. Synchronization would apply to the modulation not the carrier, though something like "automatic frequency control" keeps the frequency difference of the latter small. Oct 10, 2020 at 15:25
• Ok I get it, noise may cause some bits to arrive early or late and hence the sync required and the SPI/similar interface will trace the early or delayed bits into the stream as it was sent originally, right. Oct 10, 2020 at 15:29
• No, not really. Interference might cause bits to be "missing" but it won't change their relative timing. The synchronization problem is more about finding the first bit (or more correctly "symbol") in the transmission and possible the subsequent bits as well when the transmission rate isn't precisely known or controlled. Radio IC's with an SPI interface to a packet buffer do this "data slicing" internally. Those with a simple 1-bit (or even analog) output require you to do it in software. Oct 10, 2020 at 15:32