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PLC communication distance problems

Other Parts Discussed in Thread: OPA561, AFE032

HI 

            we developing new PLC communication module.

       we have use high power OP-AMP OPA561 for transmission control . i successfully communicate full duplex mode on only few meters like (10meter) i have to improve our design to above 100 meters any  possibilities available in improve my PLC communication module help as.

1565.CPX2.REV_2_20.05.2014.pdf

 For reference here attached schematics.  

and how to calculate maximum gain for OP amp

  • Hello vasudevan mahendran1,

    I would recommend to double check that you are using the appropriate passive components corresponding to the channel you are utilizing. In other words, a “Cenelec-A-63kHz” transmitter should be used to establish communication to a “Cenelec-A-63kHz” receiver. The other receivers in the network that are configured as “FCC-150kHz-450kHz” will receive only a very attenuated version of the transmitted signal (this could explain the short distance you are observing).

    Also, I would probe the voltage drop on terminals 2 and 6 of U4 to verify the H-bridge is not introducing unnecessary series resistance in the transmission path (ideally the voltage drop on U4 should be only a small fraction of the voltage transmitted).

    If you are trying to communicate in the “FCC-150kHz-450kHz” mode at frequencies in the high end (300 kHz and above), the OPA561 is probably not the best candidate for cases when the line impedance is low (2 ohms or less). For that frequency range and in low line impedance conditions I would recommend the AFE032.

    The detail that strikes me as problematic is when you say:

    vasudevan mahendran1
    i successfully communicate full duplex mode

    Full duplex communication using the schematic you attached will only work in a two-node network where one modem has an “FCC-150kHz-450kHz” transmitter and a “Cenelec-A-63kHz” receiver whereas the second modem has the roles swapped (“Cenelec-A-63kHz” transmitter and a “FCC-150kHz-450kHz”  receiver).

    Please bear in mind that there are many factors that play a role in the reach of your PLC communication link. Some of the factors pertain to the transmission line (upon which one has very little or no control) and some pertain to the transmitter/receiver software + hardware. For example, some of the critical factors related to the transmission line are:

    1)      Noise level on the line.

    2)      Characteristic impedance of the line.

    3)      Propagation coefficient of the line (specially the real part or attenuation constant).

    4)      Level of distortion introduced by the line and compliance of the transmission line to the Heaviside condition.

    Some of the critical factors related to the transmitter/receiver are:

    a)      Modulation scheme utilized (two of the most commonly utilized schemes in PLC are S-FSK and OFDM).

    b)      Number of bits associated per phase and number of tones utilized in the case of a phase modulation scheme; or number of tones selected and mechanism for shifting the tone in the case of a frequency modulation scheme.

    c)       Implementation of an error correction code in symbol formation.

    d)      Power broadcasted.

    e)      Sensitivity of the receiver.

    f)       Channel selectivity of the line coupling circuit.

    I do not know which factor may be the problematic one in your application so I will try to provide general guidelines.

    With regard to factor “e)” my suggestion would be to increase the gain in the block that processes the received signal on U2.

    If you suspect you have a problem with “f)” then I would suggest you review the transfer function of your transmitter and receiver filters (passive components and any active blocks in U2).

    If you still are having problems with the link reach, the next option is increasing the power broadcasted. This can be accomplished by increasing the gain in the transmit path and potentially increasing the power supply level of the transmitter (this would address “3)” and “d)” above).

    The options above would be the “brute force” approaches.

    Some more refined options would include:

    -          Find the characteristic impedance of the power line (and whatever appliances are connected to it) and adjust the transfer ratio of the coupling transformer accordingly.

    -          If the interferers on the power line land directly on or close to your transmitted frequency you can either transmit at a different frequency (assuming you are using a two-tone frequency shifting scheme), or move to a narrow-band PLC modulation scheme (such as OFDM), or incorporate error correcting codes to your symbol generation and decoding algorithms.

    Finally, I would like to encourage you to take a look at our line of PLC solutions at http://www.ti.com/plc

    One detail to notice is that our solutions are half-duplex, in other words, any node in the network can only perform one operation (either transmission or reception) at a given point in time. The C2000 microcontroller in charge of the media access control layer (MAC layer) of the PLC protocol determines when an appropriate time to transmit is and when to receive. We do not have full-duplex PLC solutions.

    Hope this helps.

    Best regards,

    Jose