Electronics > Beginners
What oscilloscope bandwidth do i need for measuring Vp-p(ripple, noise)?
spford:
Hello.
At first, My english skill is very low. Understand please.
I am a newbie about electronic circuits, oscilloscopes.
This measure is hobby at home.
## Question 1
What oscilloscope bandwidth do i need for measuring Vp-p(ripple, noise) of a 5V USB charger with a switching frequency of 500 Khz?
1. Only use the 'five times rule' -> 500 Khz x 5 = 2,500 Khz?
2. Use the 'five times rule' + Consider harmonic components -> 500 Khz x 5 x 5 = 12,500 Khz?
Which is correct at bewteen 1 and 2? or other way?
Note.
In the links below, they measure both low and high frequencies.
http://www.righto.com/2012/10/a-dozen-usb-chargers-in-lab-apple-is.html
## Question 2
What is the most appropriate for me on the four Mini Oscilloscopes?
------------------- List of four products (low price to high price) -------------------- ------
###### 1 - JYE TECH DSO 150 (Price $ 26, Resolution: 12 bit, Bandwidth: 200 Khz, 5 mV / Div, Sampling: 1 Msps)
https://www.banggood.com/Original-JYE-Tech-Assembled-DSO-SHELL-DSO150-Digital-Oscilloscope-Module-9V-p-1211151.html?rmmds=search&cur_warehouse=CN
###### 2 - DSO FNIRSI PRO ($ 40, 8 bit, 5 Mhz, 50 mV / Div, 20 Msps)
https://www.aliexpress.com/item/DSO-FNIRSI-PRO-Handheld-mini-portable-digital-oscilloscope-5M-bandwidth-20MSps-sampling-rate/32973233356.html
###### 3 - MINI DS212 ($ 85,: 8 bits, 1 Mhz, 20 mV / Div, 10 MSa / s)
https://www.banggood.com/MINI-DS212-Digital-Storage-Oscilloscope-Portable-Nano-Handheld-Bandwidth-1MHz-Sampling-Rate-10MSas-p-1202288.html?rmmds=search&cur_warehouse=CN
###### 4 - HANTEK 2C42 ( $ 102, 8 bit, 40 Mhz, 10 mV / Div, 250 MSa/s)
https://www.aliexpress.com/item/Hantek-3in1-3-in-1-2c42-2d42-2c72-2d72-Digital-handheld-Oscilloscope-Portable-40mhz-70mhz-bandwidth/32953177457.html
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Thanks for reading.
I've been browsing the internet, Youtube for a few days, but I do not know if I know what I'm sure of.
so I would like to get help from experts here.
I would appreciate for your a reply. :)
bdunham7:
I don't know about the "5x" rule, but it can be hard to determine ahead of time what sort of noise may appear in such a device. A lowpass filter that is effective at the fundamental will be even more effective at the higher harmonics, so I'd expect any ripple to be primarily at the switching frequency--or below it due to interaction with line frequency or other internal processes.
Of the 4 scopes you listed, only the Hantek one is up to your task, IMO. The first has clearly insufficient bandwidth, the second has low sensitivity and the third is marginal at best on both bandwidth and sensitivity. If you look at the Hantek's detailed specs, you'll see that it has 6 MHz bandwidth with the 1X probe. In order to get the the 10mV/div sensitivity (which isn't all that great either, but the best of the lot), you need to use 1X probing and live with the 6MHz bandwidth--which seems sufficient in this case.
I don't know your circumstances, but $100+ for a very modest (at best) scope seems a poor investment when pretty good 2-channel DSOs are available in the $250 range. Just a thought! :)
radiolistener:
You're need to multiply on 10 for pulse and square waves.
20-40 MHz bandwidth will be enough for your purpose. But for your task sensitivity requirement is more critical than bandwidth.
I'm very skeptic about these links, which you're provided.
I think first three are just a toys and will be completely useless for your task. You will not be able to see voltage ripple with it.
Don't know about HANTEK, but according to specification, it's max resolution is just 10 mV/div.
Such device will be definitely useless for your task. Because it cannot show you ripple which usually is about 1-5 mV.
Look to this review, it seems that this is also just a buggy toy, but more expensive than other.
I don't recommend to buy any of these toys, because you will not be able to measure power supply ripple with it.
I can recommend Siglent SDS1102X-E, it has almost enough sensitivity for your task.
bob91343:
Basically you need to be able to see all significant harmonics of the wave. If you are concerned about rise time, you need more bandwidth than if you just want to verify operation. As someone said, about 10 times the fundamental frequency is a rule of thumb but even that is open to question, depending on how important the fidelity is.
Since you want to measure noise, you need to make sure you can see all components of the signal that matter to you. You don't need to worry about frequencies into the microwave region unless you have equipment sensitive to those frequencies. So measuring ripple and stating a voltage value isn't as important as deciding how much you can tolerate. A very fast wave will contain high frequency components regardless of its fundamental frequency.
So a 1 ns rise will require a wider bandwidth than a 100 ns rise, even if the wave is low frequency. In other words, there is no simple answer and each case is unique.
Adrian_Arg.:
for hobby I recommend ahttps://www.ebay.com/itm/Hantek-DSO5102P-Digital-Storage-Oscilloscope-100MHz-1Gsa-S-2-CH-7-TFT-USB/292256381782?epid=2240906425&hash=item440bd67b56:g:KYkAAOSwR0xZuQg4,It's economic, a little higher but a much higher Rigol DS1054z, and of the last ones that have come out but of much higher price Sglent sds1204x-e
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