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dsl filter measurement - RF Cafe Forums
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| karthik
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Post subject: dsl filter measurement
Posted: Wed Jan 20, 2010 9:02 pm
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Joined: Tue Apr 11, 2006
8:13 pm
Posts: 39 |
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How do you measure the characteristics of a DSL
filter? I would like to know how to transition from
the RJ45 connector to a coax to look at it on a
network analyzer. Is the network analyzer the right
instrument to use? Is there any other way?
Karthik
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fred47 |
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Post subject: Re: dsl filter measurement
Posted: Fri Jan 22, 2010 11:45 pm
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| General |
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Joined: Wed Feb 22, 2006
3:51 pm
Posts: 113 |
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A vector network analyzer (VNA) with sufficient
bandwidth to cover the frequency range of interest
is certainly the best instrument to use. Not all
S-parameter test sets will work down to about 4
kHz.
Second best is a frequency synthesizer
and a gain/phase meter like the HP 3575A. These
are sometimes available on e-bay. You'll have to
do more work this way, but the equipment costs will
certainly be less.
Do note that the DSL
filter is unlikely to be a 50 Ohm device, however.
(Your comment about "transition from the RJ45 connector
to a coax" implies that you recognize that fact).
That means using either appropriate transformers
to get to and from 50 Ohms, or minimum-loss pads
(which of course will add attenuation). The transformers
themselves will have some characteristics which
you'll need to remove from your measurements. Recent
model VNA's may be able to do that automatically.
What characteristics are particularly important
to you?
Good Luck!
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karthik |
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Post subject: Re: dsl filter measurement
Posted: Fri Jan 22, 2010 11:59 pm
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Joined: Tue Apr 11, 2006
8:13 pm
Posts: 39 |
Hi fred, Thanks for the input. I am looking
to characterize s-parameters. I am aware that, as
you suggested, for a dsl splitter/filter, the impedances
on the phone and dsl lines are different and not
50 ohm. I guess I have to design a balun to go from
coax to the RJ-45 and the differing impedances.
Thanks for the input
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fred47 |
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Post subject: Re: dsl filter measurement
Posted: Sat Jan 23, 2010 12:18 am
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| General |
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Joined: Wed Feb 22, 2006
3:51 pm
Posts: 113 |
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If I remember correctly, the phone companies have
used 600 Ohms for open-wire lines (such as older
and rural systems often use), and 110-120 ohms for
cables with a large number of pairs of wires.
Transformers are available with amazing bandwidths,
if you spend enough money. Unless you have experience
designing transformers (and at DSL frequencies,
a balun is a transformer!), I'd suggest utilizing
the skills of the specialist designers.
Good
Luck!
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Posted 11/12/2012
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