Re: [RFI] DSL Filter Update

["Christopher E. Brown" <cbrown@woods.net>]

Yes, you did.  I was just providing a bit more specific info as to the 
effect.

On Sun, 8 Mar 2009, Roger Parsons wrote:

> I think I have already covered that in several postings. Of course the filter 
> is a considerable compromise in a number of respects, but a cut-off of 3MHz 
> would not protect against a 160m transmitter at all - which is where this all 
> started.
>
> 73 Roger
> VE3ZI
>
>
> --- On Sun, 8/3/09, Christopher E. Brown <cbrown@woods.net> wrote:
>
> > From: Christopher E. Brown <cbrown@woods.net>
> > Subject: Re: [RFI] DSL Filter Update
> > To: ve3zi@rac.ca
> > Cc: rfi@contesting.com
> > Date: Sunday, 8 March, 2009, 7:05 PM
> > On Sat, 7 Mar 2009, Roger Parsons
> > wrote:
> >
> > > Just to advise the group that a couple of other
> > stations have had success with this filter. Nick, VE3FJ,
> > also checked out its frequency response with the following
> > results:
> > > 1.85MHz   -26dB
> > > 3.65MHz   -46dB
> > > 7.24MHz   -68dB
> > > 14.13MHz  -60dB
> > > 21.0MHz   -56dB
> > > 28.5MHz   -54dB
> > >
> > > Of course in theory the stop band attenuation should
> > continue to increase with frequency, but in practice there
> > will be strays across the filter that will cause a
> > performance drop at higher frequencies.
> > > 73 Roger
> > > VE3ZI
> >
> > Keep in mind that ADSL2+ has signaling up to 2.2Mhz, and
> > that the default S/N threshold to use a channel is normally
> > 6 - 9 db (default varies between DSLAM vendor/model,
> > providers tune based on cable plant.  Metro area
> > providers with newer cabling and shorter runs can leave it
> > around 6, older or lower density cable plants (longer
> > average run length, more pairs feeding into single location)
> > tend to need it tweaked higher).
> >
> > 3 - 6 db rolloff at 2.2Mhz or below *will* limit the DSL
> > line max rate.
> >
> >
> > A filter with a sharp cutoff starting around 3Mhz combined
> > with heavy common mode choke would have alot less impact on
> > the sync rate.
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