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Author Topic: Lower Sync than expected - output power as minus on modem  (Read 1163 times)

TheBruce

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Lower Sync than expected - output power as minus on modem
« on: December 11, 2018, 12:03:18 PM »

Have browsed the forums for years and found them very helpful but never needed to post, hopefully someone may be able to assist.

Moved back to 80/20 with Zen last Thursday after 18 months on 40/10 with EE, but the downstream sync is lower than it used to be when I was last on 80/20, upstream is at 20k. Initially on interleave (thought it would have been wide open?) with a 67k sync (78k attainable) but that changed this morning and I am back on fastpath with a current attainable of 73k and a sync just under that.

On an ECI cab with a HG612 for now, Zen supplied the Fritz 3490, did try that at first but sync seemed lower than expected and needed more detail on the stats so I changed to the HG612.

My query is about the output power reported from the modem and dslstats, it is currently a minus figure of -1.6dBm up and down, before the interleaving was removed it was -1.4dBm for up/down. Is that normal/misreported or does it indicate an issue with the line?

I understand that attainable will be reduced as more people get on the cab but wanted to check if that was the only reason for the lower sync, or if there is another issue.

Wholesale checker shows 80-74 clean and 80-73 impacted, 225m from the cab according to the Fritz when I checked and before I moved to the 40/10 product with EE I got the full 80k sync.

Any advice would be useful and can post full dslstats later if needed, also wondering if the Fritz would be a better fit for my ECI cab?

Thanks
Bruce
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j0hn

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Re: Lower Sync than expected - output power as minus on modem
« Reply #1 on: December 11, 2018, 02:46:20 PM »

If the downstream SNRM is around 6dB then there's no more to give.
That would suggest crosstalk has eaten the difference.

The minus power isn't necessarily a mistake. A red herring, ignore it.
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burakkucat

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Re: Lower Sync than expected - output power as minus on modem
« Reply #2 on: December 11, 2018, 05:14:27 PM »

The minus power isn't necessarily a mistake. A red herring, ignore it.

Expanding a little on the power subject . . .

The power is reported in units of dBm (decibels relative to one milliwatt), a ratio. Hence --
  • A reported power of 0 dBm indicates an absolute power of exactly one milliwatt.
  • A reported power more positive (larger) than 0 dBm indicates an absolute power greater than one milliwatt.
  • A reported power more negative (smaller) than 0 dBm indicates an absolute power less than one milliwatt.
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ejs

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Re: Lower Sync than expected - output power as minus on modem
« Reply #3 on: December 11, 2018, 06:24:14 PM »

Always reporting identical output power values for up and down is a known issue, one of the values is misreported, I don't remember which one. The misreporting has no impact on what speed your line can achieve.
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TheBruce

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Re: Lower Sync than expected - output power as minus on modem
« Reply #4 on: December 12, 2018, 08:53:01 AM »

Thanks for the replies everyone, SNR is at 6.3 so I'm thinking this is the max for the line now more people are on the cab.
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