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RF transceiver chipset with low BER

Discussion in 'Electronic Design' started by john smith, Jul 25, 2005.

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  1. john smith

    john smith Guest

    I currently think of building a low power RF modem (433Mhz) + datalogger to
    collect some data. I have look around at different RF transceiver chipset
    manufacturers (chipcon, atmel, analogue device,microchip,mircel ect) and
    they are all pretty much have a BER of 10^-3. Is possible to reduce the BER
    by adding external components e.g. preamplifier on the RX pin?



    Radiometrix made ones with BER of 1 ppm! anyone know what chipset they use?



    thanks



    John
     
  2. Tim Shoppa

    Tim Shoppa Guest

    e.g. preamplifier on the RX pin?

    That will just amplify the noise too (and probably make you more
    susceptible to intermod etc.)

    The 10^-3 BER comes out in certain conditions. Increase power,
    decrease loss (e.g. move receiver closer to transmitter), lower noise,
    or lower your data rate and you get much better BER's. Shannon's law.

    Note that your real BER will be very different than the advertised one
    because you're using it in a non-lab environment.

    Tim.
     
  3. Guy Macon

    Guy Macon Guest

    Radiometrix made ones with BER of 1 ppm! anyone know what chipset
    they use?

    (Note: I am not an RF expert)

    The app note at [ http://www.radiometrix.co.uk/apps/apnt100.htm ]
    seems to indicate that a good SNR is the key to getting the BER
    down. Do you have reason to believe that the transceiver chipset
    adding noise at low input levels is a problem? If so, it would
    seem that a good preamp would help. If, on the other hand, the
    problem is too much RF noise in your band, it would seem that a
    preamp would simply amplify the signal and the noise.

    Have you considered using error correction? Look at the CRC at
    [ http://www.radiometrix.co.uk/products/bimsheet.htm#pac-data ]...

    I am sure that the real RF experts will have better suggestions.
     
  4. PeteS

    PeteS Guest

    The BER is going to be directly proportional to the S+N/N ratio. That
    will be determined by the received signal strength, although different
    modulation techniques will give a different curve of BER vs. Rx signal
    absolute strength.

    You should note in the data sheets that the BER listed (for a typical
    device from Microchip,
    http://ww1.microchip.com/downloads/en/DeviceDoc/70090a.pdf ) is at a
    specific sensitivity. For instance, it states that the BER shall be
    <=10^-3 (for a narrownband FSK signal) when the received signal
    strength is -109dBm. (Put that in perspective - it's a received signal
    power, at the device, of about 14fW).

    At higher receive signal strengths, the BER will be much better. 10^-6
    is known as 'carrier class', incidentally. for any installation with
    transmitter and receiver fairly close, you should easily achieve 10^-6
    BER.

    Cheers

    PeteS
     
  5. Think you misunderstand the spec. the usual specification for sensitivity
    is the input level to the reciever that gives you a BER of 10^-3

    you can get pretty much any BER you like, it is just a matter of how high the
    input levet is ...

    So you are comparing apples and oranges ...
    it may have a BER of 1 ppm at and input level of -80dBm, and a BER of 100ppm at -100dBm
    it is different measurements and can directly be compared


    -Lasse
     
  6. cannot be be directly compared ...
     
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