[RFI] DSL Filter Update

[Christopher E. Brown]

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 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.
>>
>>
>