ADSL Signal monitoring with an electric fence

So how much does an electric fence influence your ADSL link?

The normal voltage supplied by Telkom on a voice line is about 50VDC. For ADSL, the DSL carrier is super-imposed on the voice line and operates at a much higher frequency (300-600kHz in my tests). I built a 10:1 pre-scaler and fed the signal to an oscilloscope. Below, you can see a normal DSL carrier signal.

Normal ADSL carrier signal

Below is the exact same signal, but with my electric fence turned on. Notice the spike shown in the middle of the image:

ADSL carrier with spike present

And below is the section surrounding the spike taken with a higher sampling frequency. As you can see, the spike is about 200µs wide.

ADSL signal spike magnified

When looking at the error counts reported by my ADSL modem (the excellent DLink 300T), it reports the following:

Total RX PDU's 5753491
Total RX error counts 1407
Error rate (as a percentage) 0.02%

So the error rate is really extremely low. In addition, the spikes do not seem to affect the efficiency of my link. I have a 512kbps line (512down/256up) and I see the expected throughout of about 54kbytes/sec on a local transfer. So, although an electric fence does introduce errors on the line, it makes no real difference in practice.

Back to the workbench.

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