Section 1.7.8(D) of NET4 specifies that a +21 to +23dB (950mV) 16KHz metering pulse signal should not impair communication. The best way to ensure this would presumably be to filter out these signals using an LC filter.
Some experimentation shows that a Rockwell 288ACFL chipset can live with 0.7V r.m.s of 16KHz and possibly more, when the signal is AC-coupled to the line. This shows that the bandpass filter on the DSP input stage is quite efficient at removing 16KHz sine waves. The main obstacle to getting a good connection is the fact that if the AC 16KHz signal is greater than the DC voltage, then the DC voltage over the electronic inductor will drop to a level below which it does not function during some of the cycle which will clip the modulated data signal. What is needed is an LC filter with enough attenuation to stop this. I expect 20dB would suffice. Does anyone out there know of a ready made filter that can be bought and inserted between the DAA and the German wall socket to achieve this? Regards Ben ------------------------------ Ben Wrigley Approvals Specialist KTL Newlands Science Park Inglemire Lane Hull HU6 7TQ UK Phone: +44 (0)1482 801801 Fax: +44 (0)1482 801806 Web: http://www.ktl.co.uk/ktl Email: [email protected]
