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What is a Woosh test ?

27/11/07

What is a Woosh test ?

Permalink 07:40:53 pm by Eugene Gardner, Categories: General

Broadband connections problems ? You need to get a Woosh test mate. Your ISP can initiate this using their account with the wholesale provider (normally BT). It measures the quality of signal you are receiving using several quantitative metrics as follows.

  • Line Length.
    How far you are from the exchange. This is related to the length of the wire rather than the straight line distance from the exchange.
  • Line Loss
    Loss is measured by comparing the power level of the signal sent from one end of the line with that received at the other end. The difference between these levels is expressed in Decibels (dB). Your line must have a signal loss (noise) of less than 45dB between the master socket and the telephone exchange.
  • Capacitance
    Capacitance acts as a filter, allowing certain frequencies to pass and blocking others. In the case of telephone wires, which were not designed for ADSL use, a high capacitance level can prevent the frequencies used by ADSL from being transmitted properly. For a pass it need to be less than 180nF, but ideally it should be less than 160nF (nano-farods).
  • APTS
    This test uses special software on the engineers hardware to talk to the DSLAM and measure the attenuation across the actual line.
  • Attentuation Test
    This looks at the quality of the line across the DSL frequency range and measures how much of the signal reaches your house. The further you are away from the exchange the higher your attenuation figure will be as the signal loss increases. A downstream attenuation of less than 42 dB is needed for a fast connection.
  • Signal to Noise Ratio
    This is the difference between the level of the signal being received and the natural noise level on the line. Here, the higher the figure the better. Noise on your line is caused by many things. Some examples are other wires in the cable running alongside your wires, interference from power cables, radio signals, higher than normal resistance joints in the telephone wires and damp in the wires or cables. The downstream SNR Margin should be at least 10 dB to get ADSL, anything less than this will see frequent disconnections and other problems. Maxdsl works slightly differently and your router will try to sync at the highest speed it can whilst maintaining a safe SNR Margin.

Many ADSL modem/routers will display the equivalent of the woosh test metrics, but these can be inaccurate. Some can be as much as 20dB off, though the majority are within 2-3dB. For those with very long lines, the Signal to Noise ratio (Noise Margin) becomes critical, ideally a figure above 6dB is needed for most ADSL kit to function.

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Thank you for the wonderful article.
13/10/09 @ 11:00
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