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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