I have a 475 scope. I know the 485 is a 350MHz
scope.
?
How do higher frequency scopes work? I have been
considering using a converter in front of my 475 to work in the UHF ham band
regions.
?
I can use the down converter for lower frequency
counters also.
?
I retired as?an EE in 1998 (not
voluntarily!)
?
Bob Macklin
K5MYJ
Seattle, Wa.
"Real
Radios Glow In The Dark"?
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----- Original Message -----
Sent: Tuesday, March 04, 2014 10:03
AM
Subject: Re: [TekScopes] RE: 2400 series
probes (is p6137 the most optimal?)
?
On 04 Mar 2014 07:40:20 -0800, you wrote:
> If you have a
critical application and really need to measure with minimal effect on the
signal the only practical solution is to build a dummy plug-in probe into the
circuit with exactly the same characteristics as the scope/probe combination
that will be used for measurement, and replace the dummy with the real probe
when making the measurement. As insertion of the real probe does not load the
circuit it can be low impedance (typically 50 ohm) and so will feed directly
into your 50 ohm scope input. As this setup is easily built yourself it is a
far cheaper option than an active probe if your circuit can be modified in
this way.
Tektronix mentions a way to do this in the 7S11 manual on
page 2-14. A load or
gain setting resistor which is grounded at one end can
be replaced with an R
minus 50 ohm resistor and 50 ohm transmission line
going to the 50 ohm
oscilloscope input.
> If 500MHz scope
bandwidth is too low you may want to go to a sampling system instead of
getting a 7104. The cost should be no more, you just have to be careful with
input signal level. As sampling is inherently 50 ohm it's a great match for
the dummy probe system while frequency response and sensitivity are so much
better than the 7104, if somewhat noisier. Only good for repetitive signals
though - no good for looking at transients or finding glitches.
If you
have a persistent display you can find glitches. The low sampling rate
of
the oscilloscope may make the time required impractical though.
Digital
storage oscilloscopes with low waveform acquisition rates have the
same problem.
