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Thread: What is the Baud Rate for?

  1. #1
    boliver No Longer Registered

    Default What is the Baud Rate for?

    I noticed that there is a setting , and I've seen a post or two about the baud rate (9600) for the XTS 3000. What is that used for? How can hams use that in the hobby?


    Boliver


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    Moved to newbie area.


    Edit: Now moved to Motorola Miscellaneous, as it's beyond the scope of the Newbie forum. Redirect in place for 1-week.

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    It all has to do with trunking control channels. Not useful for hams at all (non-affiliate scan excepted). Only a few properly equipped 3000s can do 9600 but someone else would have to fill in the exact conditions. For ham exclusive use, all you'd need to check for is whether or not the radio will do P25.

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    9600 is actually the bit rate, not the baud rate. P25 is C4FM (2 bits per symbol) so the actual baud rate is 4800.

    And yes - its to do with trunking control channels, so its not really relevant to HAM use.

    Quote Originally Posted by boliver View Post
    ...baud rate (9600) for the XTS 3000...

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    Quote Originally Posted by MattSR View Post
    9600 is actually the bit rate, not the baud rate. ~
    I've always wondered about this... so why do Motorola themselves call it 9600 BAUD?

    As in "Q361 - ASTRO 25 9600 Baud Trunking Systems Operation"
    Andrew

  6. #6
    syntrx No Longer Registered

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    Quote Originally Posted by Bigfella237 View Post
    I've always wondered about this... so why do Motorola themselves call it 9600 BAUD?



    As in "Q361 - ASTRO 25 9600 Baud Trunking Systems Operation"


    Because they describe it incorrectly.

    Baud rate = symbol rate. P25 Phase 1 transmits 4800 symbols per second, with an information rate of 2 bits per symbol we get a data rate of 9600 bits per second.



    From the Daniels training guide:


    Modulating / Demodulating and Filtering
    In Phase 1, a 12.5 KHz channel is used to transmit C4FM modulated
    digital information. C4FM modulation is a type of differential Quadrature
    Phase Shift Keying (QPSK) where each symbol is shifted in phase by
    45 degrees from the previous symbol. Although the phase (frequency)
    is modulated for C4FM, the amplitude of the carrier is constant,
    generating a constant envelope frequency modulated waveform.
    In Phase 2, digital information is transmitted over a 6.25 KHz channel
    using the CQPSK modulation format. CQPSK modulates the phase
    and simultaneously modulates the carrier amplitude to minimize
    the width of the emitted spectrum which generates an amplitude
    modulated waveform.


    The modulation sends 4800 symbols/sec with each symbol conveying
    2 bits of information. The mapping between symbols and bits is shown
    below:

    Information Bits Symbol C4FM Deviation (Phase 1) CQPSK Phase Change (Phase 2)
    01 +3 +1.8kHz +135 degrees
    00 +1 +0.6kHz +45 degrees
    10 -1 -0.6kHz -45 degrees
    11 -3 -1.8kHz -135 degrees
    Last edited by syntrx; Feb 19, 2013 at 10:14 PM. Reason: Daniels, not Thales

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    Because they're wrong, and exhibit so much corporate arrogance that they can't figure out that they're wrong.

    Quote Originally Posted by Bigfella237 View Post
    I've always wondered about this... so why do Motorola themselves call it 9600 BAUD?

    As in "Q361 - ASTRO 25 9600 Baud Trunking Systems Operation"

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    I think the mistake actually happened this way...

    The 3600 systems are 2 level FSK, 1 bit per symbol, which means that the 3600 bits per second systems actually are 3600 baud.

    P25 is 9600 bits per second, 4800 baud but people just see the 9600bps and naturally assume its 9600 baud... without really understanding what it means
    Last edited by MattSR; Feb 20, 2013 at 12:20 PM.

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    Seems logical... you could probably throw into the mix some marketing people with little technical ability who never let the facts get in the way of a good marketing strategy?
    Andrew