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Jason Bowers Jason Bowers is offline
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Default tests to do on used oscilloscope?

On 5/3/21 10:04 AM, Ralph Mowery wrote:
In article ,
says...

my signal generator outputs some wonky voltages unless you have a load
resistor across the outputs. It's 600ohms in a box with 1" spacing banana
plugs and receptacles. I could never figure out why that's not handled by
a pushbotton.

Also, make sure you don't have any knobs pulled out putting you in zoom
mode. My signal generator has one of silly scope knobs too for some
reason.



Signal generators are designed to put out a certain voltage into a
certain load. Think of them as having a signal generating source of
zero impedance in series with a resistor. Any load will devide between
the internal impedance and the load impedance.

For RF generators there were two standards. One was an open circuit Or
very high impedance) voltage and the other was for a 50 ohm load. My
service monitor has a software setting to do either one. It is from the
old analog cell phone days and 30 years ago the cost was about $ 50,000.
When the cell phones went digital the service monitor was put out for
surplus and are selling for under $ 1000 now on the used market.

When using a scope you have to allow for the peak or peak to peak ratio
to the RMS value of a sine wave. As mentioned before I don't recall the
ratio as I seldom need it and the scope I have now will calculate it and
put on the display. If your RMS meter shows abot 120 volts AC out of
the wall socket a scope will show around 170 volts peak.



Well, I've been using a coax T. On one end, there's the 50 ohm dummy
load, other side is input from the URM 25 signal generator, and the
final side goes into channel 1 of the scope. I wonder if I should use
some sort of a buffer here, on the side leading to the scope, like a
voltage divider, etc, rather than direct? Or, perhaps actually check
from the "open circuit" output on the generator as the URM has that too?
Yes, I'm now compensating for PP by converting to RMS after I see the
waveform. It may be closer than it was, but will know with more
certainty after the probes arrive today.

A small 1x 10x probe arrives today at last so I can at least check the
scope's square wave output signal peg. See what happens then.

The frequency still seems to be showing higher than it actually is
though. Even with a 30 Mhz scope like this, should I be able to "zoom"
in to see just one or two waveforms? So far, I can't seem to get closer
than 4-5 waveforms at 28 Mhz even with the 10x magnifier on.