Data transmission...without a module of some sort

Wireless & IoT
1

I have been looking around online for the past several months on this sort of stuff and I have not found much on transmitting data over longer distances. I know there are modules that can transmit far (XBee pro), but I would like to design something myself since that is infinitely more fun.

Since I do most of my stuff using PICs (currently a PIC24FJ256GB108 or PIC18F4550), I have been looking at BPSK for a modulation since it seems to be the easiest to do for binary-based systems such as a microcontroller. I understand the basic concept of BPSK: A one is a positive sine of the RF wave and a 0 is the negative sign of the wave, switched at the zero point. My basic idea is to connect the UART of a PIC running at a low baud (1200 maybe) and be able to send small snippets of data long distances (a mile or more) assuming the device is in the open air (e.g. in a R/C plane). So far the simplest schematic of a BPSK modulator I have seen is this one:

http://www.mlecmn.net/~lyle/bpskmod.gif

The whole thing basically functions as a really big XOR gate (3 of the gates are ganged together to get more output apparently). However, since it uses a logic gate and an RF signal is analog, I do not see how this would work.

Another schematic I have seen this one (too big, so its a link):

http://home.swipnet.se/~w-41522/lfbeacon/schema.gif

It is a complete schematic for a BPSK transmitter. I would like to understand how it works. Since I have no background really in radios and stuff aside from the things I have already done with WirelessUSB, could someone explain how this works?

How is demodulating accomplished?

Has anyone else done anything like this before?

Sorry for all these questions, but I finally got enough information that I could post something.

2

BPSK is often used for high-speed amateur packet radio.

It should have an LP filter on the PA output, to avoid interference.

There are various ways to demodulate BPSK signals.

It would be illegal to use it in most countries unless you have an amateur radio license.

Leon

3

I am in the USA and I am under the impression that as long as I use either the R/C band, 900Mhz band, or the 2.4Ghz band I am safe licensing-wise. Is this true?

4

That modulator won’t work at 900 MHz, 2.4 GHz or the RC frequencies. I think it’s intended for the VLF amateur band.

Leon

5

leon_heller:
That modulator won’t work at 900 MHz or 2.4 GHz or the RC frequencies.

Leon

Well I said I didn't know very much :?

Well than when does that modulator work?

6

I think it’s for the 136 kHz amateur band.

Leon