Re: Wrong cable... How bad is it?


G Hopper
 

This is an interesting thread since I, like Stephen, have long assumed my
cables were ok. I'm no longer 100% sure and need to check them.

However, what REALLY caught my attention was Jon's comment "For use over 20
MHz eg with SG503 or SG504 or fast pulses like PG506, a calibrated
special 1/2 m Tektronix cable is preffered..."

Having one of those devices, and not having the special cable, what's the
solution?

Is the solution to the issue: getting/building a cable (with 50 ohm coax)
of exactly 1/2m length? or is it something else? There must be a solution
other than acquiring an original cable since Tektronix would have had a
specification and had cables made to that spec. I've got to believe that
it's something that mere mortals can reproduce. :-)

If it is, where can one gather the information?

Cheers,
Grant

On Mon, Feb 8, 2021 at 2:09 PM Jean-Paul <jonpaul@ix.netcom.com> wrote:

Stephen welcoming to the wonderful world of wired transmission of Signals,
researched since the earliest days days of Telegraph, telephone and vidéo.

First, câble Zo is important in a matched system eg 50 ohm cal gen and 50
ohm load.
For audio tests with 1 M Ohm , no difference.

As the frequency, and bandwidth go up, and rise times get short, the Zo
is more and more critical to obtaining low reflections, as is the cables
VSWR, attenuation and phase vs legnth and frequency.

Thus RG174/u is 50 ohm, but dia ~ 3 mm so rather high atten. db/ meter,
while RG58/u, is thicker and RG6/u very thick 12 mm so much mess atten per
m thoughts all are 50 Ohm.

For use over 20 MHz eg with SG503 or SG504 or fast pulses like PG506, a
calibrated special 1/2 m Tektronix cable is preffered . Generally the
shorter the cables the better for cal use.
Finally the wire and insulation quality and connectors precision are
factors.

We use the Tektronix and Genrad precision cables for critical applications
and avoid the cheap, poorly made Chinese clones.

Suggest that you consult the Belden Wire site papers and applications
notes, as well as the detailed specifications on whatever cables,
connectors and wire you use.

Bon courage

Jon








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