[RFI] DSL Filter Update

[Roger Parsons]

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 at woods.net> wrote:

> From: Christopher E. Brown <cbrown at woods.net>
> Subject: Re: [RFI] DSL Filter Update
> To: ve3zi at rac.ca
> Cc: rfi at 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.
> 
>