What not to buy....
We had an ADSL line running at ~600 kbits/s downstream speed instead of the expected 3M. The christmas tree of extensions, phones and faxes didn't help but replacing the T-shaped Excelsus Z-200UK microfilter with a better one (ie any other type of filter) allowed the modem to achieve 3.6 Mbits/s downstream - result !
Our ISP replaced the filter, we took it to bits after reading up at ADSLnation and discovered that the Z-200UK is a poor design where the input wires on pins 3 and 4 of the BT socket are passed out to the same pins on the output socket, neatly bypassing the filter circuitry. If you study the photo below you can see the offending red and green wires, with the black and yellow signal pair (2 & 5) going through the filter. The testmeter showed a low resistance DC path from the centre two input to the output pins, the other (better) filters we tested were open circuit between these points.
BT's filter spec SIN346 specifically requires that this bypassing is avoided "The bell wire must either be filtered by the filter or left open at the Line Port of the filter and re-created at the Telephony Port of the filter" so the Z-200UK is a non-compliant non-effective item.
So don't buy (or be given) an Excelsus Z-200UK, ask for their Z-420UK-A or Z-420UKP2J instead, where all the wires go through the filtering in the approved manner.
For the anoraks - the problem caused by this is that RF interference collected in the extension wiring or from the phones etc on the line will pass along the bell wire, through the filter into the master socket and then through the ring capacitor into the signal wire, greatly reducing the SNR of the ADSL signal.
We had an ADSL line running at ~600 kbits/s downstream speed instead of the expected 3M. The christmas tree of extensions, phones and faxes didn't help but replacing the T-shaped Excelsus Z-200UK microfilter with a better one (ie any other type of filter) allowed the modem to achieve 3.6 Mbits/s downstream - result !
Our ISP replaced the filter, we took it to bits after reading up at ADSLnation and discovered that the Z-200UK is a poor design where the input wires on pins 3 and 4 of the BT socket are passed out to the same pins on the output socket, neatly bypassing the filter circuitry. If you study the photo below you can see the offending red and green wires, with the black and yellow signal pair (2 & 5) going through the filter. The testmeter showed a low resistance DC path from the centre two input to the output pins, the other (better) filters we tested were open circuit between these points.
BT's filter spec SIN346 specifically requires that this bypassing is avoided "The bell wire must either be filtered by the filter or left open at the Line Port of the filter and re-created at the Telephony Port of the filter" so the Z-200UK is a non-compliant non-effective item.
So don't buy (or be given) an Excelsus Z-200UK, ask for their Z-420UK-A or Z-420UKP2J instead, where all the wires go through the filtering in the approved manner.
For the anoraks - the problem caused by this is that RF interference collected in the extension wiring or from the phones etc on the line will pass along the bell wire, through the filter into the master socket and then through the ring capacitor into the signal wire, greatly reducing the SNR of the ADSL signal.
posted by PhilT at 2:22 PM
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