On Mon, 28 Feb 2011, J.Gordon Beattie, Jr., W2TTT wrote:
> Chris,
>
> We have seen cases where people do put bandwidth-limiting devices ahead of
> the DSL modem in an effort to keep specific frequencies out of their modem.
> The result may be more permissive for Amateur Radio operation, but can
> reduce the overall bandwidth available for the DSL service, which can make
> the service more vulnerable to other noise or line performance-driven
> impairments.
Same here, fairly recently spent a good 4 hrs having a discussion with a
"RF Engineer" at a broadcast/repeater location. Had constructed 4
common/diff mode filter blocks (4 pair eGSHDSL) that were...
1) Based on the ADSL1 freq range
2) Attempted to shunt everything outside of the range...
The root causes were actually...
Poor wiring practices between the demark and the modem location.
Untwisted 30ga in wall wiring. Routing each wire in the pair in "color bundles"
between 66 blocks, path seperated by more than 6 inches, different
distances due to routing...
Moving the path from demark to modem onto the 4 pairs in exising cat3
cables and using twisted pair with clean routing between 66 blocks took
care of 90% of the issues, leaving a moderate UCE rate. Grabbing 4 2.4"
#31 toroids from home over lunch and wrapping 30 turns of 24ga pre twisted
to about 4tpi at the modem end on each pair took care of the rest.
If nothing else, it was an amusing break from the normal work flow, as I
recall I was originally supposed to have been moving a remote POP from
NxDS3 transport to 2xOC12 that day.
Another one was a guy that insisted on installing line to ground MOVs to
"protect" his gear. Course they were quarter sized things with a 20V
clamp. They would clamp on ring, and were enough of a capaciter to shunt
the DSL signal as well.
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