From: John Fisher ([email protected])
Date: Fri Oct 20 2000 - 11:31:13 PDT
Ron,
Certainly shorter is better! Depends on what you are looking for.
Soldering the coax shields together helps as if it were a passive diff
probe, which it also is in case of TDR, ensures that any noise picked up
on one shield is not seen as differential mode noise back at the scope
but as CM and thereby rejected due to CMRR. Keeping everything
between TDR & DUT as short as possible ensures fastest edge and most
resolution of closely spaced physical/electrical points of
interest.
John
At 05:40 PM 10/19/00 -0700, Ron Miller wrote:
John
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soldering the shields together every 3 inches implies some multiple of
that.
Much better to keep the length below 3 inches so as to not roll off the
TDR
edge. That is why the extension cables are needed to allow the head
to get
near the work.
Ron Miller
> -----Original Message-----
> From:
> Sent:
> To:
> Cc:
> Subject:
>
> Fabrizio,
>
> We have built these using equal length sections of semi rigid coax
with sma's at one end. The semi rigid copper outer shield is soldered
together approx. every 3 ". Prepare the ends by careful
cutting of the shield with an exacto knife, than solder the center
conductors to the launch point vias or pads. Tektronix shipped some
of these to us as accessories when we bought their IPA-510 a few
years ago. I might be able to find a tek part number but someone
like Micro-Coax could make some for you or find an off the shelf semi
rigid assembly with sma's on both ends and then just cut it in half. Be
carful not to bend it too much and kink it. These can also make
nice 50 Ohm 10x passive probes with the addition of a series 450 resistor
at the end.
>
> Regards
>
> John
>
> At 03:44 PM 10/19/00 -0400, you wrote:
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*********************************************************************
> John M. Fisher -- Cisco Systems -- [email protected]
> 170 W. Tasman Dr., Bldg G, San
Jose CA 95134-1706
>
__
_
_
> ________///
\_/ \________/ \ ____
>
\/
> Manager Signal Integrity, Enterprise Line of Business
> 408-527-9186, Page 408-308-5501, Fax 408-526-5504,
N6PFN
>
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