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Re: [RFI] DSL Filter Update

To: ve3zi@rac.ca
Subject: Re: [RFI] DSL Filter Update
From: "Christopher E. Brown" <cbrown@woods.net>
Date: Sun, 8 Mar 2009 20:34:36 -0500 (CDT)
List-post: <rfi@contesting.com">mailto:rfi@contesting.com>

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 

73 Roger

--- 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

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

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

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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