[RFI] 160M RFI - 4 khz combs-
pfizenmayer at q.com
Sat Dec 19 23:45:59 EST 2015
RE: the earlier message about 160 M carriers popping up with keying
I found the following about VDSL2 :
DMT divides signals into 247 separate channels, each 4 kilohertz (KHz, or 1,000
cycles per second) wide. One way to think about it is to imagine that the phone
company divides your copper line into 247 different 4-KHz lines and attaches a
modem to each one. You get the equivalent of 247 modems connected to your
computer at once!
Each channel is monitored and, if the quality is too impaired, the signal is
shifted to another channel. This system constantly shifts signals, searching
for the best channels for transmission and reception. In addition, some of
the lower channels (those starting at about 8 KHz) are used as bidirectional
channels, for both upstream and downstream information. Monitoring and
sorting out the information on the bidirectional channels, and keeping up
with the quality of all 247 channels, makes DMT more complex to implement
than other carrier technologies, but also gives it more flexibility on
lines of differing quality.
They do use channels in the 160 meter band and other ham bands and even
talk about RF ingress issues from hams and RF egress to hams.
Sounds like what I may have - although I have not hard any modulation on those
carriers , perhaps they are just "holding places" . Question is why it just started up
a few days ago - will try to find out something from Centurylink but they have been
very hard to deal with on other issues. Unable to ever reach anyone past the filters .
Walking the alley with a homebrew ferrite rod ant and my little IC R10 rx the carriers do
peak at each pole that has a drop .COX cable lines also run the same pole line -
not inconceivable it might be something they are doing . Both plants are really sloppy
with rats nests of wires and unused drops just cut off and hanging ..
More information about the RFI