Here's a handy bit of info from B&K pertaining to this situation...
"Why isn't the output voltage correct?...
Many function generators are designed with a 50 ? output impedance. This is because the common RF connection cables (e.g., RG-58/U) have characteristic impedances of 50 ohms. Some generators have adjustable output impedance. The amplitude of these generators is correct when the generator's output is terminated in a load that matches the output impedance. Thus, if you first terminate the output with the proper feed-through terminator, you'll measure the same voltage as the generator's setting. If you operate a 50 ? impedance generator into a high impedance input, such as an oscilloscope with a 1 M? input impedance, you'll see approximately twice the stated generator output. A quick test is to put a non-reactive resistor (e.g., a carbon film resistor) across the output terminals of the suspected output impedance of the generator and check the voltage output across the termination resistor. Be careful not to exceed the resistor's power rating."
"There's a lot of ringing on my pulses/square waves...
You probably have an impedance mismatch. Another symptom is that the measured amplitude on the scope won't match the generator's setting (see the previous question).
When you input a signal using coaxial cable into an oscilloscope with a high input impedance, you should terminate the coaxial cable with a 50 ? feedthrough termination at the oscilloscope's input. If you omit the termination or put it on the output of the generator, you will have an impedance mismatch at the other end of the cable (where it connects to the scope) and you will see ringing on fast rise time edges. If you don't have a 50 ? BNC feedthrough termination, a 50 ohm carbon film resistor will work fine; don't exceed the power rating of the resistor."
-----------------------------------------------------------------------------------------------------------------------------
One of my older audio signal generators needs to have its internal 600 ohm termination switched on for its output meter to read correctly. As far as measuring the signal level of some of my sig-gens, I cannot use any of my DMMs because their AC bandwidth is pretty poor.
I keep a vintage piece of HP gear around so I have at least one meter that can measure the amplitude of high frequency signals. My HP410c has a 700MHz bandwidth (useful out to 1.2GHz according to HP). Unfortunately, I do not have a high bandwidth scope on by bench (yet).
Regards,
Frank
Very good Frank. I appreciate your input. I have a High Z setting that
I used to get a proper reading.
As I tested all capabilities of the Instek AFG-2225, I eventually got to
the "ARB" (Or Arbitrary) section of the unit. Utilizing some of the "Built-In"
wave forms. I found after setting 3 parameters, Start, Length and (forgot
the button name but it's the Vertical setting of the wave), then pressing
"Done" according to the User Manual, found after hitting "Output" that the
voltage & wave form failed to display on my Instek GDS-1072a-u!
Yes I set the Scope triggering properly! Even did an :gasp: "auto-set" on
the Oscope. But after 2 days, no wave/volts. On the 3ird day however,
the AFG-2225 ARB output worked for an hour.
I shut it down, turned it on, waited 30 mins. warm-up... In the ARB section
again, set the parameters, hit the "Done" button, hit the "Output" button
but NO volts/wave on the Oscope.
Ok, so now awaiting RMA # and return. So this review will have to wait.
The only lack I can say so far is that the AFG-2225 has 120/M samp, 10bits
and a 4K waveform length creation. 4K! :sniff:
It's a nice unit though, I'm happy what it does. It has good features and
works with the Instek GDS-1072a-u scope.
I did take some Scope pics. I will have to get the USB stick, which I forgot
and upload some results. But I didn't do a robust review yet with the unit
because of the hiccup. ..hey what's this! .oO(
) ..Situation!
ACvolts
p.s. The Instek Oscope GDS-1072a-u is made in Taiwan, but the AFG-2225
is made in China. The scope has better Q&A. So it's not surprising that
the AFG-2225 had Sum Ting Wong with it.