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@audiosystemsgroup.com> wrote:
>
>
>> From: Jim Brown <jim@audiosystemsgroup.com>
>> Subject: Re: [RFI] DSL Filter Update
>> To: "rfi@contesting.com" <rfi@contesting.com>, "Roger Parsons"
>> <ve3zi@yahoo.com>, "ve3zi@rac.ca" <ve3zi@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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