Interesting at the academic level but, considering that end-user equipment is being used in non-laboratory conditions, I would not consider results at that level of precision. You have, however, made your point clear to me.

My overall feeling is that the average end-user, using the average end-user equipment, will only notice significant changes in the SNRM -- when a telephone loops the pair -- under fault conditions.

Edited by burakkucat (Wed 01-Feb-12 12:49:58)

Those drops (0.2 dB and 0.6 dB) I would class as insignificant and nothing to be concerned about. If the drop was more that 1 dB, then I would wonder . . .

Was thinking similar, any variation of under 1dB I usually ignore in peoples stats.

The noise environment even ignoring on/off hook phones is not constant, if it were then algorithms would be used to filter it out and thus use even lower signal levels and reduce cross-talk

I have performed my own experiment. I have:

* a SSFP (an ADSL V1.0) fitted at the NTE5/A
* a total of three telephones (two 20CN, one 21CN)
* a 2Wire 2700HG

With all telephones "on-hook", the 2700HG shows --

Text
1 23 4	Current Connection:         Current Noise Margin:            5.8 dB                  7.3 dB        Current Attenuation:            45.7 dB                 27.3 dB         Current Output Power:           19.6 dB                 12.5 dB

With one, two or all three telephones "off-hook" there is absolutely no changes to any of the above reported values. Just to be sure, I refreshed the screen three times for each test.

For the record, one of the 20CN telephones is a 300-series, dated 1956. I was surprised to see that one had no effect.

Edited by burakkucat (Wed 01-Feb-12 13:06:31)

How do you define 20cn abd 21cn telephones?

The century in which they were manufactured.

Ah, that makes sense - nothing to do with the normal meaning of 20/21cn in the BT/ broadband sense then