Bill C. "Impairments on Outside Plant Wiring".
Bill -
Thanks for the link to Bell Labs, lot's of good info. I can use all the help I can get in continuing to understand all the complexities of
DSL Line Coding, Transmission, etc.
I wish I could Burn Steve Macica's DSL knowledge into a PROM and plug it in. Sure would make things much easier.
On the HAM radio issues, the information provided under "Impairments on Outside Plant Wiring" as I expected, does not discuss the issue of
CAP's effect on Short Wave and Amateur Radio, it only discusses HAM's effect on DSL transmission. As I would expect coming from a CAP oriented document.
The point I have tried to convey when discussing interference of SW and HAM in VDSL transmission is the point that CAP interferes with these two common types of communication. (more prevalent in Europe than the US, though HAM is still a very popular pass time for many Americans I believe Walt/ Steve S will a test to this).
And for those who do not know, Short Wave is very big in Europe. Just ask Radio Luxembourg which transmits 1,400,000 watts on Short Wave which can be picked up here in the US, I believe you'll find it on the 49 meter band.
They only speak English a total of 4hrs a day during two different periods, but put on a great show.
Back on track>>>>>>>>>>>>>>
CAP side of the story..
"RFI is caused when signals emanating from local or international
broadcast systems (such as AM, HAM, and shortwave radio) couple onto the UTP in the outside plant. The effect of the interferer is to place a strong narrowband signal into the spectrum of the signals. Experimental studies have shown that most of the RFI tends to be generated in the drop cable (especially flat-pair wires) or at connecting points in the communication link between the ONU and the home. The UTP distribution cable itself does not seem to be significantly prone to ingress. Table I shows HAM radio bands that are likely to be problematic."
"Impairments on Outside Plant Wiring" lucent.com
DMT's Story.
VDSL AND RFI
With a DMT-based VDSL system it is not necessary to have a transceiver "react" to RFI by adapting to it during operation. One example: Transmission in the DMT sub-channels that correspond to amateur radio bands can be prohibited permanently by taking this into account in the design of the transceiver. ( P. Chow and John Cioffi :
"Broadband digital subscriber lines" IIR Maximizing Copper Conference, London (March 1995). This principle of blanking out transmission at certain frequencies has had to be used by some cable companies to avoid interference (to and from) amateur radio enthusiasts.
As with ADSL, the performance of a Basic DMT VDSL system can be increased by around 6dB via the use of trellis coding, echo cancellation, optimized transmit power distribution and larger DMT sub-channel constellations. Although greater transmit power would further increase performance, the scope for this is limited with VDSL,
since transmit power significantly greater than + 10dBm would be prohibited by EMC emission constraints and worst case pair balance. This is lower than ADSL transmit power levels because VDSL operates at frequencies where the copper cable becomes a more efficient radiator."
(note: a point where I believe CAP leaks, effecting amateur radio and short-wave transmissions JW).
techstocks.com
Perhaps Steve Macica could shed some light on this issue?
I am not qualified to take a firmer stance. I provide the best I can, with the research I have done. But research and a basic understanding is not a substitute for expertise such as Steve's.
JW@KSC |
