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Measurement of patch cable / terminating impedance - RF Cafe Forums
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mbergmann
Post subject: Measurement of patch cable / terminating
impedance Posted: Tue Jun 20, 2006 5:18 am
Captain
Joined:
Mon Jun 19, 2006 10:27 am
Posts: 7
Hello,
I've to measure
the properties (return loss, cross talk) of patchcables,
which are
assembled with typical RJ45 connectors as well as with other kind of
'differential' connectors, such as Firewire, USB or industrial round
connectors.
RJ45 isn't a problem, but there are no instruments available
with other
connectors. So I thought about constructing such an adapter
on my own. Starting from a network analyzer I would connect a SMA-connector
to a balun going further to the desired connector. The following problem
occurs:
- Because I've got different types of connectors I'll
need several
adapters. To provide an easy operability it would be
convenient
if all adapters are located on just one circuit board
with one
sma-connector. With the help of a switch I want to choose
which
connector is currently connected with the sma-connector. So
I need
something like a power-divider, 1-to-8 (8 as an example).
But I don't believe that this is sufficient, because the signal will
first
be divided and the parts of the signal which travel to the
branches which
currently are not connected with no connector will
be reflected at the branch ends. So the branches have to be terminated
with the line impedance.
How do I achieve, that a branch can be connected
with a connector or
alternatively with the impedance ?
(if
you don't understand my description, please have a look at
http://www.dcmindustries.com/highspeedd
... leindx.htm,
they offer such system, it's just too expensive )
Top
Stephen
Post subject: Measuring patch cablesPosted:
Thu Jun 22, 2006 12:28 am
Captain
Joined: Wed Jun 21,
2006 8:33 pm
Posts: 21
Location: Queen Creek, Arizona
First
off: I could not get your link to work..missing page
I am not
quite sure how to answer your question but I would offer an alternative.
If all you are trying to do is measure impedance and s-param's of different
cables, I would simply design a two layer board (easy for building accurate
strip-lines), and SMB connectors (They can be easy to use unless you
do not mind threading on and off SMA's). Then design several traces
from the SMB's to the various cableing connectors (RJ45, USB, 1394),
at the same time you could construct each pair of traces that allow
for terminating with shorts, opens (if needed thur's) for easy calibration
and deembedding of the boards and your adapters themseles. I personally
would avoid the switch, not because it is impossible to do what you
are doing, but because it would still be a deembedding risk and stray
parasitics could be problematic). That would be the beauty of SMB's,
as easy to use as a switch unless your automating the system.
So my adpater would be a two layer board, with 2 smb's and 2 connectors
for each type of cable, two traces for each cable type (port 1 and port
2) obviously connecting the smb's to the cable jacks, with the possibility
of jumpering for a short calibration.
I apologize if I misunderstand
what you are attempting to do and this repsonse is of no use.
_________________
CMOS RF and Analog ESD Specialist!
www.srftechnologies.com
Top
mbergmann
Post subject: Posted: Thu Jun 22, 2006
4:27 am
Captain
Joined: Mon Jun 19, 2006 10:27 am
Posts: 7
Thanks Stephen for your answer !
What you described
matches quite well my intented assembly. Unfortunately I don't know
how do insert an image in this forum, that would simplify of my project.
But I realized that I don't need a power-divider, something
like a switch (doesn't need to be automatic) would be sufficient.
Pin-diode or a GaAs-switch are too exaggerated, so I believe a HF-Relay
would be the right thing ? What kind of 'mechanical' switches are available
?
[/img]
Top
Stephen
Post subject: Posted:
Thu Jun 22, 2006 9:03 am
Captain
Joined: Wed Jun 21,
2006 8:33 pm
Posts: 21
Location: Queen Creek, Arizona
In some
of the other forums, this manufacturer was recommended:
http://www.hittite.com
There was also a pretty detailed response rgerading impedanced matched
switches.
_________________
CMOS RF and Analog ESD Specialist!
www.srftechnologies.com
Posted 11/12/2012
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