Topband: QRM from DSL?

[Bill Tippett]

        I forwarded a copy of my note to K1DG who works at Analog
Devices and he responded as follows.  Sure glad we had some hams including
Doug involved with this early on!

K1DG wrote:

The ADSL group here is just down the hall from my office (I am working on
wireless chips these days). When they were first working on this stuff, one
of them came down to me and wanted to know about typical field strengths
from ham transmitters, and typical received signal strengths in ham
receivers, etc. 

I think this was in the context of developing the algorithms for the
receiver cited in the patent.

Occasionally over lunch, we talk about such things, and it turns out that
the ADSL standards bodies are well aware of the implications of wide-band
comunications on a long twisted pair. Ingress due to hams, etc., is a
concern because it will obviously cause subscribers to gripe about crummy
service. 

Egress (especially in the ham bands) is a concern because a lot of the guys
working on this stuff are hams, and they all know that hams are a very vocal
bunch with excellent connections in the regulatory bodies both in the U.S.
and elsewhere. There are masks that restrict the amount of energy
transmitted in the ham bands and it turns out to add measurable complexity
to the system.

There was an excellent article in the March 2000 issue of the IEEE
Communications magazine on the subject. It showed the results for various
methods of reducing the emissions from the xDSL waveform in the spectrum
occupied by the ham bands. The article was written by a team of engineers
from Alcatel (an ADI competitor and customer in ADSL!). It is very clear
from the article that these guys recognize the issues. When they describe
amateur radio, they specifically mention that hams have "very sensitive
receivers".

                                                73,  Bill  W4ZV



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