Maker Pro
Maker Pro

LeCroy or Tek scope?

J

Jim Yanik

Jan 1, 1970
0
What causes the false appearance of ringing on a scope trace? Is it
just simply the ground loop created by the earth wire or something
more?

the inductance of a too-long ground lead will cause false ringing.
 
J

John Larkin

Jan 1, 1970
0
Make your own.

I use a sma-sma dc-block and a ~0.085 semi-rigid coax with an sma connector on
one end. The other end's ground shield is stripped back an 1/8 inch exposing the
center conductor. This is a "RF Sniffer". DC block I use is good up to 18ghz.

If you plug one of those small 950-ohm Caddock non-inductive resistors
into the end of an SMA female, you get a nice 6 GHz 10:1 passive
probe. Even a carbon comp works pretty well.

And a good fet probe is magical; you can probe a lot of ecl-type
circuits with no ground clip at all. I should think that a homemade
GaAs fet probe wouldn't be hard to make... maybe use one of the neat
NEC dual-gates, NE25x39, with g2 to source for really low Cin.

The best is an SD-14 sampling probe, something like 0.2 pF at the tip.

John
 
G

Gilbert Mouget

Jan 1, 1970
0
dated Sun, 07 Mar 2004 10:55:25 -0800,
If you plug one of those small 950-ohm Caddock non-inductive resistors
into the end of an SMA female, you get a nice 6 GHz 10:1 passive
probe. Even a carbon comp works pretty well.

I think you need a Z0 termination at both ends of the coaxial
cable.
 
J

John Larkin

Jan 1, 1970
0
dated Sun, 07 Mar 2004 10:55:25 -0800,


I think you need a Z0 termination at both ends of the coaxial
cable.


You need it at the scope end, but not at the tip. The scope-terminated
coax looks like a near-perfect 50 ohm resistor at the far end, so the
950 ohm resistor feeding into the coax looks like a flat 20:1 (oops...
not 10:1) voltage divider. 450 ohms gives 10:1.

That's how the Agilent 54006A probe works.

John
 
G

Gilbert Mouget

Jan 1, 1970
0
dated Sun, 07 Mar 2004 15:04:02 -0800,
You need it at the scope end, but not at the tip. The scope-terminated
coax looks like a near-perfect 50 ohm resistor at the far end, so the
950 ohm resistor feeding into the coax looks like a flat 20:1 (oops...
not 10:1) voltage divider. 450 ohms gives 10:1.

That's how the Agilent 54006A probe works.

You are right, if there is no reflexion from the scope then
you dont need 50 ohms on the tip side.
 
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