[RFI] DSL Filter Update

[Larry Benko]

I have designed many devices in the T1/E1/DSL arena.  The line impedance 
for lines (without bridged taps) was always 110 to 120 ohms.  The slight 
variation was due to the lines being 22, 24, or 26 gauge wire.  You 
could easily use an N2PK VNA with lossy resistance matching that was 
calibrated out to find the real S21 response.  It WILL be different than 
the 50 response.

73, Larry, W0QE


Roger Parsons wrote:
> I know that Nick used an N2PK VNA - .png attached - but no more than that. I did do a few sums on the filter design a few weeks ago and was surprised to find that the design impedance is close to 50 Ohms rather than the 600 Ohms that I had been expecting - or that I had been expecting until I thought about the likely characteristic impedance of two closely spaced small insulated wires. But even if the wrong source/load impedance is used the shape of the passband/stopband will not change - only the overall attenuation.
>
> 73 Roger
> VE3ZI
>
> --- On Sat, 7/3/09, Jim Brown <jim at audiosystemsgroup.com> wrote:
>
>   
>> From: Jim Brown <jim at audiosystemsgroup.com>
>> Subject: Re: [RFI] DSL Filter Update
>> To: "rfi at contesting.com" <rfi at contesting.com>, "Roger Parsons" <ve3zi at yahoo.com>, "ve3zi at rac.ca" <ve3zi at rac.ca>
>> Date: Saturday, 7 March, 2009, 2:42 PM
>> On Sat, 7 Mar 2009 11:29:05 -0800
>> (PST), 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.
>>>       
>> Roger,
>>
>> Exactly how was the response measured?  What source
>> and load 
>> impedances?
>>
>> 73,
>>
>> Jim K9YC
>>
>>
>>
>>     
>
>
>       
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