Adding waveform onto PLC

[eduf]

Hello everyone,

This is my first topic here, so I hope to be done everything well.

I am testing a PLC (Power-line communication) transceiver operating onto a 12V power line and in order to assure it is according to protocol specifications some testing steps defined in the specs must followed.

The test of the receiver defines that the PER (packet error rate) must not exceed X% when the swept carrier waveform is received in the presence of a constant carrier interfering signal occupying a range producing a SINR (signal-to-interfering noise ratio) of 3.0 dB.

Trying to be succinct what I have to do is to find a way to add this waveform onto the power-line.
The frequency I chose to add was 120KHz.

I first tried simply putting both signals in parallel, but as my signal generator has a limit of 10V it not surprisingly showed a message of voltage overload on output connector.

Then I tried to use a clamper circuit assuming the PLC signal is majority DC, then noise would be the AC part. The circuit I used was a simple clamping with diode as shown in the following picture:


The problem is that the waveform that after the clamping the waveform generated by the generator is been attenuated as you can see below. These are images from my scope. I kept the channel 1 in DC coupling mode then the 12V DC can be visualized.

PLC waveform:


Signal generator waveform - 120kHz 1Vpp:


Waveform after clamper circuit – PLC and waveform 120kHz 1Vpp:


Zoom at waveform, you can see it is been attenuated:


Waveform after clamper circuit – PLC and waveform 120kHz 7Vpp:


Zoom at waveform:


Could you please give me suggestions or correct me if I am doing anything wrong?
Is this method the one you would recommend me in order to add the PLC and sine waveforms?