General > General Technical Chat
The Rigol DS1052E
rossmoffett:
Today I made two BNC cables and ran them in parallel to ch1 and ch2 from the sine wave generator. I tried to take measurements about every 1/2 MHz, but usually at least 1 MHz. The higher resolution gives some really interesting results!
For starters, I have to admit my test faults. I tried to keep three significant figures and a filled screen for precision, so every now and then I would adjust the attenuator on the sine wave generator. If you see both ch1 and ch2 moving, that's what's going on. It could also be because I switched ranges, or because the generator is generally unstable.
But.. look around the peaks. When my modded channel peaks, my unmodded channel drops, and vice-versa! What's going on here? Also, because I took the data to 150 MHz, you can see that there may be additional filtering going on somewhere.
Around 100 MHz, my modded channel starts dropping while the unmodded channel stays pretty constant. I think this should mean that I've succeeded, but what's going on before that?
Any ideas?
Dave, haven't heard from you in this thread for a while. ;)
jahonen:
I suppose you didn't use any terminator at the scope end? Failure to do this will result reflections, which ruin your otherwise perfectly good data. Check also that the generator has 50 ohms output impedance. It looks like that you got the reflection peaks/valleys perfectly measured, just as the transmission line theory predicts, though. :)
For the record, when we measured my colleagues 100 MHz Rigol (using a VNA as a signal source) using that kind of terminated setup, we determined the -3 dB frequency to be about 170 MHz. Otherwise it was pretty flat.
Regards,
Janne
rossmoffett:
So THAT'S what those are for!
Thanks. :D
170 MHz stock?? That's amazing!
jahonen:
Yes, it was perfectly stock when we measured it. I think that it is quite normal to have shallow roll-off. For example, for my 300 MHz Agilent MSO6034A, the calibration measurement report says that at nominal 300 MHz, test pass limit is -3 dB and actual measured value is -0.8…-0.6 dB.
Regards,
Janne
rossmoffett:
I tried adding a 50 ohm resistance in my BNC cables and I still get that signal ghosting to some degree. Using my probes I don't get that effect, but I feel like I can't really be sure about this hack until I can compare it to a quality scope. I guess I'll have to borrow one with some commercially made BNC cables, but I still only have access to a 100 MHz unit.
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