Radio Frequency Transmitter

Discussion in 'The Projects Forum' started by JeffreyPeter, Jul 25, 2012.

  1. JeffreyPeter

    Thread Starter New Member

    Jul 25, 2012
    Hi friends I am in need to design a radio frequency transmitter and reciver working in simplex mode. the transmitter must be capable of transmitting min of 128 bytes, then the range could be up to 10 - 20 m...... I would like to know which digital modulation method I should use or if I can use any rf module .......
    Thanks in advance :)
  2. Blackbird

    New Member

    Jul 25, 2012
    In conventional RF modules used two methods of digital modulation. The amplitude and frequency. In the first case corresponds to the presence of one carrier and its lack of zero. In the case of frequency modulation unit presented the same frequency as zero but the other carrier is emitted in the air constantly. Spacing between the frequencies is as far as I remember 30-40 kHz.
    Everything is wonderful on the transfer but the main nasty begins when you receive. The developers of these modules have to tear off arms and legs for this. Because all of the problems with the reception and demodulation of the bed on the shoulders of those who will use these modules.
    The fact that the vast majority of these modules work in a free range of 433 MHz. And there are already people sitting at each other on the head so the places without a signal the receiver catches the din and the roar of the adjacent modules of the same.
    So the question for the amplitude modulation of the signal is simple - if your able to closely spaced signal transmission module to beat his neighbor, and thereby ensure the reception of the carrier and pauses without interference or not. For carrying out there just after the detector goes to komarator and further transported to the austere logic level ..
    Therefore, for normal transmission is not enough just to pass a digital signal - it is necessary to introduce into it some redundancy and error-correcting codes so that it was possible to restore the original sequence of bits from the noisy signal
    Frequency modulation of Law Considered more noise immune than the amplitude. But that's the joy in RF modules carefully killed developers receivers. In the first post immediately after the transmitter, we should not pass any useful information or just to drive the air one or zero.
    and all because a few milliseconds or even longer the receiver must adjust the level of automatic gain control, and only then can correctly receive the signal. But this difficulty does not end.
    In the RF receiver module FM transmission is not constant component. This means that you can not pass a long string of zeros or ones - because if you do it after a while the signal at the receiver output will randomly switch from zero to one - lovely!
    Therefore, in addition to the original error-correcting codes still need to convert a sequence of transmitted bits so that there was no constant component. For example use code manchester.
    And of course all the questions of the initial encoding and decoding on the shoulders of the bed by the RF module. I have already encountered this trash and the next time I will need to tie to the radio device, I'll buy a ready-made radio modem
    JeffreyPeter likes this.
  3. Kermit2

    AAC Fanatic!

    Feb 5, 2010
    So, would those problems you specify be overcome with a different encoding scheme for the data.

    FSK perhaps?
  4. JeffreyPeter

    Thread Starter New Member

    Jul 25, 2012
    think I will go with the module Tx and Rx ...