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Bandwidth check of my oscilloscope with simple means ?
Fungus:
Blah, blah.
I just did it with a capacitor shoved into an Arduino and I got very consistent times around the 3.5ns mark. :)
(on my 100MHz Micsig)
tggzzz:
--- Quote from: Fungus on December 11, 2020, 10:31:55 am ---Blah, blah.
I just did it with a capacitor shoved into an Arduino and I got very consistent times around the 3.5ns mark. :)
--- End quote ---
What did you do with the capacitor?
I'm not surprised about the risetime; modern jellybean CMOS is faster than most people imagine. Especially those that toggle the output at 1Hz and think they have a 5Hz bandwidth waveform (5*fundamental frequency, cough).
2N3055:
This is second topic with exactly same question from OP.
This one also devolved into discussion about creating fast pulses, like most of them..
Again, answer to OP question, no, there is no simple improvised way to measure -3dB point of scope front end without leveled signal generator.
If you had 200-500 signal generator with decent amplitude accuracy across the frequency (like SDG6000X or similar) you could fairly well estimate what the curve is.
OP never explained what he wants to accomplish or why he asked the question. Without that it is hard to help him.
Berni:
--- Quote from: tggzzz on December 11, 2020, 10:05:36 am ---Circuit with imperfect but useful measurements (<300ps risetime): https://www.eevblog.com/forum/testgear/show-us-your-square-wave/msg1902941/#msg1902941
--- End quote ---
Yep it works great for testing oscilloscopes up to about 500MHz, for higher up it becomes too slow.
For going faster i would recommend just buying Leo Bodnars fast pulse generator:
http://www.leobodnar.com/shop/index.php?main_page=product_info&products_id=295
I have two of them (SMA and BNC version) and they are great little generators for making ridiculously fast pulses. Well worth the pretty low price of them. Being small is also a nice thing since you can bring the generator to where it is needed rather than using a cable (the regular garden verity coax cable really degrades the rise time of pulses that are this quick)
EDIT:
Also one way to level a wobbly freqency response signal generator is to use one of these:
https://www.keysight.com/en/pd-1000001913%3Aepsg%3Apro-pn-8472B/low-barrier-schottky-diode-detector-10-mhz-to-18-ghz?cc=SI&lc=eng
This takes in a high frequency RF signal and AM demodulates it into a DC voltage while having a pretty flat and stable frequency response. So you can use this DC voltage as feedback to adjust the signal generator to the same level at various frequencies.
These RF detectors can sometimes be picked up cheep on the used market.
Fungus:
Here's the results from a coin cell battery held like this:
The capacitor was 100% necessary to get a good time. Without it I was getting results in the uS range.
Results are much less consistent for some reason (maybe because I'm touching the wires and both sides of the battery) but it can be done.
Here's my best one:
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