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POTS Volume decreases as frequency increases.

POTS Volume decreases as frequency increases.

POTS Volume decreases as frequency increases.

So I am having a strange issue.

I support faxing at a site that occasionally needs to fax. The problem is the volume of the fax decreases as the audio frequency increases. I've attached two audacity screenshots to assist in explaining. Our LEC tech currently has no clue what could be causing this issue. This is only occurring when called between local numbers, it does not occur when the call is placed long distance/outside the city. I have already ruled out the fax hardware by swapping equipment, still has the same issue.

Is there any reason a POTS line would behave this way?

RE: POTS Volume decreases as frequency increases.

If this was done with a tone generator to send tone there is no way that a 1000 cycles should be at -30db, other than that the chart looks correct. It should drop off after 3K, that's the limits of a voice circuit


RE: POTS Volume decreases as frequency increases.

Yes 3K is the bandwidth of a normal voice circuit.
If there is DSL or Broadband on that circuit then you will get a steep falloff after 3K due to filters fitted.
These filters allow the remaining bandwidth to be used for the Broadband circuit.

RE: POTS Volume decreases as frequency increases.

I should have specified, what I mean is between 610Hz and 3k the volume drops as the frequency increases. All other sites hold the same volume across those frequencies. Attached is screenshot of a good fax to help if I am explaining wrong.

RE: POTS Volume decreases as frequency increases.

Try dialing the area code (even though it is local) to see if the call is routed out through the correctly working circuits

RE: POTS Volume decreases as frequency increases.

How is this POTS line provisioned? Is it conventional copper, a loaded pair, non-loaded pair, from an ATA, derived from VOIP or SIP, from a channel bank? Or from a digital CO switch or a softswitch? More details are needed...


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