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[les-70]

  I have got used to running with modems that allow a max sync speed to be set but want to do the same on two (an HG630 and HG658B) whose firmware does not support it.  I seem unable to get very far.  I have a RJ11 splitter so I can make a second connection in parallel with the feed to the modem.  I tried connecting a RF3 in a one sided way via this and it gives about the right sync speed drop of about 10Mb/s on my connection. i.e. 75 60 65.  So good so far    but on removing it I loose sync  .  I wondered if removing an inductance from the DC 50V was the cause so I tried a 0.01 micro-farad capacitor in series with 300 ohms.  This only gave a a tiny sync reduction of perhaps 0.5 Mb/s but removing it still lost sync.  With the same capacitor and 900 ohms there was not really any discernible impact and although a bust of errors was produced it did hold sync on removal.  It looks like any significant rapid change upsets the signal.

  I am wondering on trying a potentiometer to slowly add impedance in front of the RF3 but worry that any resistance wobbles that it gives may be enough to cause a loss of sync.  Does anyone have any thoughts on a way of giving a small but safely removable impairment to a connection?   I think I may be looking for a way of adding noise e.g. with a reliably bad LED light or Ethernet over mains device

[les-70]

  To answer my own question a multiturn potenimeter and a capacitor in series with the potentiometer and connected across the dsl pair works quiet well.  The values I used for FTTC were a 470 ohms potentiometer and a 470 pf capacitor.  The capacitor ensures no dc impact and the value used gives about 9 ohms impedance at 17mhz.  With the potentiometer set at about 45 ohms prior to connection I then get a sync and attainable speed drop of about 8 Mb/s.  You can then slowly increase the potentiometer resistance to 470 ohms which gives a negligible impact on the attainable but leaves the lower sync.   

  It would be much better to use a  --maxDataRate command but if that is not available it gives the same effect.