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I am trying to build a communication system over a power line using FSK. I want to stay within the frequency band A of the CENELEC protocol which goes from 3 to 95 kHz. I am trying to determine suitable modulation frequencies for the space and mark signals. The bitrate should be 2kbps.

I'm looking for trade-offs which I should consider when choosing this frequencies but I can't seem to find anything really specific (in theoretical or equation form), other than the bandwidth.

Do you guys know of any other considerations when choosing these frequencies, other than that the demodulator should be able to demodulate the signal, such as signal to noise ratio, bit error probability, etc?

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I'm looking for trade-offs which I should consider when choosing this frequencies but I can't seem to find anything really specific (in theoretical or equation form), other than the bandwidth.

There are no trade-offs that are general in nature. The bandwidth of 3 kHz to 95 kHz for any one particular installation will, very specifically, have some spectral areas that are more suitable than other regions. Then, for instance, down the street, someone else using that bandwidth will find that their "optimum" points in the available spectrum will be totally different to yours.

In other words, a particular PLC system will find areas of the spectrum that are suitable for its transmission and avoid areas of the spectrum that are not suitable. What makes one part of the spectrum suitable and another unsuitable is totally dictated by the specific loads, supplies and wiring regimes in that particular application and not by any generalizations.

Then, on another day, the PLC system might change to use different parts of the spectrum to suit the prevailing interference on that day. It might even recalculate the hot-spots to avoid at an almost minute-by-minute timescale.

Do you guys know of any other considerations when choosing these frequencies, other than that the demodulator should be able to demodulate the signal, such as signal to noise ratio, bit error probability, etc?

If the transmitter (the master device) sends out a specific message using two particular FSK frequencies and receives a report back from the recipient (the slave device) then it can be assumed that those frequencies are somewhat usable in the short term. This has to be repeated as often as is necessary to ensure that those two frequencies remain fairly usable.

A decent PLC system will continue (in the background) to "test" other frequencies that might be relied upon as a fall-back. It's not beyond the realms of possibility that both master and slave will passively examine all parts of the available spectrum to check for interference and transfer those "findings" between each other so that there is a fall-back position should comms be suddenly lost.

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  • \$\begingroup\$ I understand that when choosing the frequencies care should be taken to what frequencies are available on the channel. The question comes more from a practical point of view. So how would one go about setting up the requirements for the distance between the two modulation frequencies. When looking from an implementational point of view. \$\endgroup\$
    – luukito
    May 3, 2021 at 11:29
  • \$\begingroup\$ @luukito I think you are missing the point of what a PLC system will do (or should do). It should do this automatically but, if designed not to do that then you have a flaky system that might work on one day but won't work for the rest of the week. \$\endgroup\$
    – Andy aka
    May 3, 2021 at 11:31
  • \$\begingroup\$ @luukito I think we are done here so, please read this: What should I do when someone answers my question? \$\endgroup\$
    – Andy aka
    Mar 6, 2023 at 15:27

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