WTB(UK): Equipment to measure nV and uV on a scope.  - Page 1
Forum section: electronics / general

author: trevwhite
author_rank: Frequent Contributor
timestamp: January 14, 2018, 09:22:38 pm
content: Bit vague but not sure of devices out there. I need to see traces of uV and nV resolution on my scope. Frequency of interest is up to 10Mhz. Seen some old Tek modules before but can't remember them now. What's about?Thanks.TrevThanksTrev

author: khs
author_rank: Regular Contributor
timestamp: January 14, 2018, 09:55:30 pm
content: Maybe 7A22: 1 µV/div, 1 MHz max.Here you find some information about the old gear:http://www.amplifier.cd/Test_Equipment/Tektronix/Tektronix_Test_Equipment.htm

author: bd139
author_rank: Super Contributor
timestamp: January 14, 2018, 10:15:45 pm
content: Sounds like you need a broadband RF amplifier. Assuming it is terminated at 50 ohms that is.

author: tggzzz
author_rank: Super Contributor
timestamp: January 14, 2018, 10:48:18 pm
content: Your first task is to understand and quantify all the noise sources, e.g. thermal noise and shot noise in your bandwidth.Your next task is to understand and quantify the interference sources, me how you will reduce them.Then you can start to think about how to measure them, if that is even possible.

author: trevwhite
author_rank: Frequent Contributor
timestamp: January 15, 2018, 12:03:47 am
content: Quote from: khs on January 14, 2018, 09:55:30 pmThanks. This or the AM502 maybe. I already have a frame for that.ThanksTrev

author: MarkL
author_rank: Unknown
timestamp: January 15, 2018, 03:19:16 am
content: Here's the manual for the AM502:http://w140.com/tekwiki/wiki/AM502In particular, take a look at the noise specs. The spec is 25uV (12uV typ.) for a BW of 10Hz to 1MHz. If your signal is repetitive and you can tolerate a lot of averaging, you might be able to do something with this amplifier. But if you're looking for sub-uV resolution @ 1MHz with a single shot, there's no way.

author: trevwhite
author_rank: Frequent Contributor
timestamp: January 15, 2018, 09:46:39 am
content: 25uV is out of range for my needs. Thanks for that.It seems the 7A22 is better.ThanksTrev

author: tggzzz
author_rank: Super Contributor
timestamp: January 15, 2018, 10:59:32 am
content: What Johnson and shot noise are you expecting from your source?

author: trevwhite
author_rank: Frequent Contributor
timestamp: January 15, 2018, 11:02:50 am
content: No idea. All a learning process and more of a curiosity really. Seems like I need to understand noise a lot more for this particular range of voltages.ThanksTrev

author: trevwhite
author_rank: Frequent Contributor
timestamp: January 15, 2018, 04:22:17 pm
content: If I go with a 7A22 then I need to find a frame for it? Anyone suggest a cheap frame?

author: khs
author_rank: Regular Contributor
timestamp: January 15, 2018, 05:38:46 pm
content: Some measurements with in a 7A22 in a 7854: 1 MHz BWBoth Inputs to GND: 20µV pp.One input open: 60µV pp.With the 7854 mainframe it's possible to average:Both inputs to GND:Averaged 10 x: 5µV pp.Averaged 100 x: 2µV pp.But you need an external trigger, because the trigger source is not averaged so you cannot trigger on noise...Maybe the 7A22 and the 7854 are hard to get, so my suggestion is to make a preamplifier with an opamp - something like the AM502.

author: MarkL
author_rank: Unknown
timestamp: January 15, 2018, 05:40:29 pm
content: I don't want to be the continual nay-sayer, but the 7A22 is only marginally better than the AM502. The 7A22 has a noise spec of 16uV (source impedance of 25R or less). The 7A22 manual is here:http://w140.com/tekwiki/wiki/7A22As mentioned on the page, the 7A22, AM502, and a bunch of other Tek differential plug-ins share the same basic circuit design, so they are all going to have similar noise characteristics.Perhaps if you described more about the signal you want to measure and what equipment you already have, it would be possible to make some suggestions.

author: egonotto
author_rank: Super Contributor
timestamp: January 15, 2018, 05:55:12 pm
content: Hello,Forget the 7A22 it is like the AM502.And the noise is RMS, p-p-noise is much more.A 50Ohm resistor with 10 MHz bandwidth gives you about order of 10 uVpp noiseLook from ElektronikSchwache Signale verstärken - das geht nicht immer !Read the Low Level Measurements Handbook from Keithley:https://www.google.de/url?sa=t&rct=j&q=&esrc=s&source=web&cd=1&ved=0ahUKEwiU39jcwtrYAhWE1SwKHaSyAHgQFggnMAA&url=http%3A%2F%2Fdownload.tek.com%2Fdocument%2FLowLevelHandbook_7Ed.pdf&usg=AOvVaw0zjAfKG6q54Ou_cIEoQpqbBest regardsegonotto

author: trevwhite
author_rank: Frequent Contributor
timestamp: January 15, 2018, 06:27:09 pm
content: Have taken all replies as being informative and really appreciate people taking time to pass on knowledge.Thanks

author: woodchips
author_rank: Frequent Contributor
timestamp: January 15, 2018, 06:59:26 pm
content: Spectrum analyser in zero span mode?

author: _Wim_
author_rank: Super Contributor
timestamp: January 15, 2018, 07:39:54 pm
content: The SRS560 (http://www.thinksrs.com/downloads/PDFs/Catalog/SR560c.pdf) has an 1MHz bandwidth and a 4nV/rootHz noise figure. So at ful bandwidth this results in 4µV of noise (squareroot(1Mhz-0Hz)*4nV/rootHz=4µV) . When you know the frequency of the the signal of interest, you can use both the internal low and high pass filter to lower this noise even further.These go somewhere between 600€ and a 1000€ on Ebay...