another somewhat related question: is there any reason to have the 50 ohm adapter for a scope being used on relatively low frequencies (<100MHz) ? what specific circumstances require a 50 ohm adapter?
It all depends on your frequency and cable length, say, for 30MHz, the wavelength in free air is 10M. Assuming you are using RG316 test cable, then the effective wavelength is 7M.
As a rule of thumb, 1/10 wavelength and longer cable calls for attention on signal integrity, so as long as your cable is longer than 2ft, you will need to terminate it properly.
There are some BNC terminators on eBay, rated up to many gigahertz. For SMA connector you will have more choices. They generally cost <$10 for a used branded or a new unbranded.
thanks for the replies!
Say I had a hi-z scope (the DS1054)... and a 50 ohm coax cable signal that I wanted to measure....
Would I be able to plug the high-z probe into a coax "T" with one side terminated with a 50 ohm terminator, and the other receiving the 50 ohm signal - and get a proper measurement?
thanks for the replies!
Say I had a hi-z scope (the DS1054)... and a 50 ohm coax cable signal that I wanted to measure....
Would I be able to plug the high-z probe into a coax "T" with one side terminated with a 50 ohm terminator, and the other receiving the 50 ohm signal - and get a proper measurement?
Depends on the frequency - if it isn't too high this may be fine depending on what you want to do.
Can you give us a more detailed example?
Added: https://www.youtube.com/watch?v=OiAmER1OJh4.
another somewhat related question: is there any reason to have the 50 ohm adapter for a scope being used on relatively low frequencies (<100MHz) ? what specific circumstances require a 50 ohm adapter?
another somewhat related question: is there any reason to have the 50 ohm adapter for a scope being used on relatively low frequencies (<100MHz) ? what specific circumstances require a 50 ohm adapter?
I see you've gotten all kinds of theoretical answers to your question. Here is an actual test case. ....
another somewhat related question: is there any reason to have the 50 ohm adapter for a scope being used on relatively low frequencies (<100MHz) ? what specific circumstances require a 50 ohm adapter?
I see you've gotten all kinds of theoretical answers to your question. Here is an actual test case. ....
That's great info, thanks for taking the time to post it.
In this case, you knew your signal source was 50 ohms. When poking around in a random circuit board, I assume the high impedance setting is preferred? Do you have an example of a circuit-analysis situation where there's not an obvious 50 ohm BNC connector.... where one would need an impedance adapter?
thanks again for your responses.
cheers
I don't know if the DS2000 is the same as the DS1000Z, but try this...
o 1MHz sine
o set the modulation to FM
o modulating frequency 1kHz
o modulate with triangle
o deviation 1MHz
Added: https://www.youtube.com/watch?v=OiAmER1OJh4.
Another Dave video! Awesome. thanks
I also came across this National Instruments white paper "Select the Correct Oscilloscope Probe for Your Application":
http://www.ni.com/white-paper/14825/en/
edit: as internet links sometimes change, I've attached the NI Whitepaper
I'm sorry but that's nonsense, BW is as much as important as sample rate.The two should match. If there's a serious mismatch then that's a red flag. You have to wonder who designed the device.
Well, 25 years ago I knew the people that designed HP's front ends, and they certainly weren't fools.
If you want to consider the maths of sampling real-time signals, don't forget that if you have an AM audio signal on a 100MHz carrier, you only have to digitise it at ~40kS/s to completely reconstruct the signal. Of course the sampler has to have bandwidth >100MHz.
@gojimmypi:
Please allow me to recommend TEquipment as your USA vendor for the DS1054z. You really _can_ beat Amazon, I think. (Someone will send you the EEVblog TEquipment discount code if you ask for it....)
ETA: Two things: I had to return my original DS1054z under the TEquipment warranty (bad glitch on one channel) and had a replacement in hand in less than a week. And I just took delivery of an Extech LT300 light meter that someone else ordered for me from Amazon... and it arrived with a previously-opened and resealed box, a completely dead battery, and a clumsily reattached screenprotector film..... but it was sold as new.
Please be advised that with Rigol you have an Exclusive 30-day money back guarantee will allow you to fully test your investment to make sure it works for you. If it does not meet your expectations, give us a call and we'll work out the return or offer a better solution.
In other words, for the first 30 days after you receive your unit, we will administrate the warranty repair or replacement.
After the 30 days, your warranty is with the manufacturer.
QuoteIf you want to consider the maths of sampling real-time signals, don't forget that if you have an AM audio signal on a 100MHz carrier, you only have to digitise it at ~40kS/s to completely reconstruct the signal. Of course the sampler has to have bandwidth >100MHz.
Agreed. AFAIK HP had (low sample rate) sampling scopes with 1GHz bandwidth back in 1960.
My old HP vector voltmeter uses similar front end technology and offers 1GHz BW and it dates back to the mid 1960s.
Sampling information systems are not new, GHz sampling systems have been around in instrumentation and systems for over 50 years now. What has changed is the data centric technology world of today putting real world analog conversion to bits of data central to many information systems today.
I came across this article & thought I'd share for any future readers of this thread regarding the high impedance vs 50 ohm oscilloscope input topic:
"What's Wrong with my Function Generator? (hint: nothing)"
http://www.effectivebits.net/2011/12/whats-wrong-with-my-function-generator.html
IMHO people still build very low sampling rate and very high BW scopes nowadays. This is the only feasible way to get low cost and very high BW scopes. A good example is PicoScope 9000 series, with 10G BW and only 1M sampling rate.
With real time technology there is no way to get such a piece of equipment at only $9000.