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Author Topic: Interpreting DMT Graphs  (Read 3175 times)


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Interpreting DMT Graphs
« on: October 04, 2008, 11:47:20 AM »

I have attached a snapshot image of my stats taken using the DMT tool.  I am on a fairly long line (~50 dB attenuation).  What I am particularly interested in are the gaps in my spectrum.  Are these acceptable bearing in mind my long line, or is something not quite right at the higher frequencies? 

I'd also like to know why I have a single tone sitting at 725 kHz.  Do these gaps in the spectrum, and the large gap from 656 kHz to 724 kHz indicate interference problems, or is this type of spectrum indicative of a long line?


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Re: Interpreting DMT Graphs
« Reply #1 on: October 04, 2008, 12:17:19 PM »


Gaps appear when there is too much noise at a particular frequency to fill the bin.  If a particular bins SNR (note this is SNR not SNRM)  is below 6dB then the router wont use that channel.  This could be due to interference.. or it could be just too attenuated to receive a signal.

Whilst I understand the very basics of DMT modulation, Im not an expert as it also involves some further complicated modulation techniques that would probably require a degree in the subject to understand fully
- but looking at your graph it looks like the decline is normal due to attenuation (loop loss/line length). 
However why you get the one strong signal further on - sorry I dont know :(

Please do not PM me with queries for broadband help as I may not be able to respond.
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