Author Topic: RS RTM3K vs RTA4K  (Read 1050 times)

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Offline metebalci

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RS RTM3K vs RTA4K
« on: March 01, 2021, 12:40:13 pm »
Because the noise figures are not published for RTM3K and what I saw in a few places were quite close to published numbers of RTA4K, I am wondering if that is the reality. Would you pick RTA considering its price (~20% more expensive for -not very clear to me but claimed to have- lower noise and 2.5x more memory) over RTM ?
 

Offline 2N3055

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Re: RS RTM3K vs RTA4K
« Reply #1 on: March 01, 2021, 02:14:32 pm »
Because the noise figures are not published for RTM3K and what I saw in a few places were quite close to published numbers of RTA4K, I am wondering if that is the reality. Would you pick RTA considering its price (~20% more expensive for -not very clear to me but claimed to have- lower noise and 2.5x more memory) over RTM ?
What do you want to do with scope? What kind of work?
What bandwidth, what kind of analysis options...?

RTM3K and RTA4K are expensive scopes, and in that price class there are alternatives that might be better for the work you do..

That being said, , those scope are identical (probably same main board) and only difference is more memory on RTA4K.  They also share very limited use of segmented memory, and no searches on common serial protocols...

So I would do a bit more research before committing...
 

Offline metebalci

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Re: RS RTM3K vs RTA4K
« Reply #2 on: March 01, 2021, 03:11:06 pm »

I am already using RTB@300Mhz for some time, and quite happy with it. RTB's MSO/digital part, serial decode etc. is enough for me at the moment and I think it is quite similar if not same in RTM and RTA as well. I wish AWG goes higher but it seems most oscilloscope are like this. The main reason I am looking for another scope is bandwidth and 50 ohm inputs.

So my ideal scope at the moment would actually be up to 1.5-2Ghz (but 500M/1G is enough for me now, just to leave room for upgrades), AWG up to 100Mhz or so and normal MSO/serial decode capabilities and some second hand market for probes. As far as I can see, bw>1G ones are way more expensive so that brings me down to 1G ones. I didnt see any with significantly more capable AWG, and I guess I need to get a separate signal generator in the future. The second hand market for probes is definitely problematic with RS. The reason I am asking this question now is that the promotion for RTM and RTA is still on, and I dont see anything comparable in the same price range considering the options, I definitely need MSO, basic but some serial decode, and at least not too small sample memory.
 

Offline YetAnotherTechie

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Re: RS RTM3K vs RTA4K
« Reply #3 on: March 01, 2021, 03:39:36 pm »
RTM3K and RTA4K are exaclty the same software, same board, same components, same memory, only less memory is enabled on RTM. I would be surprised if you find a unit were typical noise is diferent, but they must exist, because RS put it as datasheet spec, noise in my RTM is within RTA spec. Oscilator on RTM can be calibrated to match RTA. With RTA you get quite better probes and maybe a full calibration certificate instead of a 2 page one. If you need bandwith, get bandwith, all the software features don't really make up for that. Any external AWG is better than the build in, which is not that flat, and has no internal or external sync.
 

Offline egonotto

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Re: RS RTM3K vs RTA4K
« Reply #4 on: March 01, 2021, 03:52:52 pm »
Hello,

look at
https://www.eevblog.com/forum/testgear/difference-between-rtm3k-com4-and-rta4k-com4/msg2428128/#msg2428128

In my opinion the RTM and RTA use the same board. They have both 4GB of sample memory but RTM can not use the whole memory.

The great difference are the probes.

Meanwhile exist scopes from Le Croy with much better noise at lower sensitivity.

WaveSurfer 4104HD 1//div has only 4.7mV rms at 50 Ohm wherat RTA has 31.4mV (but RTA has 10 divs , 4104HD has 8 divs)

Best regards
egonotto

 

Offline metebalci

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Re: RS RTM3K vs RTA4K
« Reply #5 on: March 01, 2021, 04:14:30 pm »

Good point, I asked to the shop about the probes to be sure. Did you decide to buy one of them, or 4104HD ? 4104HD can also be an option for me but it is easily 1.5x price including the MSO option.
 

Offline nctnico

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Re: RS RTM3K vs RTA4K
« Reply #6 on: March 01, 2021, 04:53:13 pm »
Passive probes are meh anyway. Dime a dozen so don't base any purchase decission on it. Given you already have an MSO you could skip the MSO part on the new scope and concentrate on bandwidth. Also be aware that Lecroy scopes are typically geared towards analysis; be sure to give one a good test especially if you want to use it as a daily driver. When it comes to Lecroy maybe the money for an MSO option is better spend on an analysis package to further complement the RTB2K you already have.
« Last Edit: March 01, 2021, 04:56:49 pm by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline metebalci

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Re: RS RTM3K vs RTA4K
« Reply #7 on: March 01, 2021, 05:21:17 pm »
Just on time, I was looking at the specs of 4104HD and for MSO it says max input freq. is 125Mhz, whereas even on RTB2K it is 300Mhz. Isnt 125Mhz too low at this level ? or this is something else.

I was thinking to keep only one scope on my bench, but maybe I should not, I dont know.
 

Offline nctnico

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Re: RS RTM3K vs RTA4K
« Reply #8 on: March 01, 2021, 05:31:28 pm »
I have 4 oscilloscopes each with their strong and weak points. Looking at the specs of the Lecroy 4104HD: I'm missing a trigger jitter specification (which the RTM3k and TA4k are not specifying either). If you want to look at small timebases (<1ns/div) then you want a very low trigger jitter otherwise a signal becomes a vertical blur. It seems to me the  Lecroy 4104HD is intended for low noise applications and not necessarily high frequency. However, there is another way to circumvent the noise level and that is by using an external amplifier.

All in all you have to decide which route to go: low noise or high frequency. The scopes you found so far do well where it comes to noise and resolution but not for high frequency measurements.
« Last Edit: March 01, 2021, 05:35:15 pm by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline metebalci

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Re: RS RTM3K vs RTA4K
« Reply #9 on: March 01, 2021, 06:25:46 pm »
I wasnt aware of such a spec (thanks for mentioning). It seems it is only specified for higher series in RS, for RTE, RTO, which says <1ps. The screen has 1280px, so 128px/div, for 1ns/div, each px is roughly 8ps so the jitter has to be under half of this is a good approx. or there is a better way to understand it ?

Which scope at this level would you say it is for high freq. use ?
 

Offline egonotto

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Re: RS RTM3K vs RTA4K
« Reply #10 on: March 01, 2021, 06:33:10 pm »
Hello,

@metebalci:
I have a RTA since 20 month
I don't know whether I buy one today.

@nctnico:
"However, there is another way to circumvent the noise level and that is by using an external amplifier"
But you can not increase the SNR with an external amplifier.

Best regards
egonotto


 

Offline metebalci

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Re: RS RTM3K vs RTA4K
« Reply #11 on: March 01, 2021, 06:36:10 pm »
Passive probes are meh anyway. Dime a dozen so don't base any purchase decission on it.

Actually that was exactly the reason I didnt buy a high bw scope before because I thought high bw probes are a must and they are expensive, adding more to already expensive scope. I was thinking I should get a Tek or Keysight so I can find second hand probes. After that I learned about z0 probes, so maybe it can help maybe not, I dont know.
 

Offline metebalci

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Re: RS RTM3K vs RTA4K
« Reply #12 on: March 01, 2021, 06:38:48 pm »
@egonotto, any particular reason you are not happy with it ?
 

Offline egonotto

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Re: RS RTM3K vs RTA4K
« Reply #13 on: March 01, 2021, 08:08:54 pm »
Hello,

@metebalci:
The precondition changed. As I bought the R&S® RTA4K-COM4 it was a special offer. But they even lower the price since than.

RTA is for R&S low end. They don't exhaust the potential.

FFT is not so good as it can be.
No search function for protocols.
Only basis trigger.
Mathematik only basis.
They can give you 500MS memory if they want.

At 100mV/div I have 30-35mV noise p-p so 5 from 10 bits wiggle. What is the benefit from 10 bit ADC?

Perhaps it is better to buy a Siglent SDS2104X Plus for the basics and if you need more BW you can additional buy a used scope for this.

Best regards
egonotto



 

Offline nctnico

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Re: RS RTM3K vs RTA4K
« Reply #14 on: March 01, 2021, 08:24:27 pm »
@nctnico:
"However, there is another way to circumvent the noise level and that is by using an external amplifier"
But you can not increase the SNR with an external amplifier.
Yes and no. At the lowest sensitivity ranges you can get better noise performance.

At 100mV/div I have 30-35mV noise p-p so 5 from 10 bits wiggle. What is the benefit from 10 bit ADC?
That is several times worse compared to the spec; there is something wrong with this number. Also keep in mind that you get the lowest noise at low bandwidths.
« Last Edit: March 01, 2021, 08:29:27 pm by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline egonotto

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Re: RS RTM3K vs RTA4K
« Reply #15 on: March 01, 2021, 09:04:22 pm »
Hello,

the  30-35mV noise p-p is peak-peak and 1 MOhm. The spec say only about rms.

Best regards
egonotto

 

Offline metebalci

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Re: RS RTM3K vs RTA4K
« Reply #16 on: March 01, 2021, 09:16:25 pm »

I thought it is not possible to measure error pk-pk and that is why it is always given in rms. Did you check the rms value, is it like in the spec in that case ?
 

Offline egonotto

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Re: RS RTM3K vs RTA4K
« Reply #17 on: March 01, 2021, 10:16:33 pm »
Hello,

enclosed a picture from my RTA.

1MOhm, full BW, 10 MS memory.

Noise is random. So each measurement differs. But in practice one can good work with it.

In the picture for the 1031 measurements rms is between 3.51mV and 3.62mV and p-p is between 28mV and 39mv.

The spec tell 4.7mV rms. But the spec tell no further condition over used memory or timesetting

Best regards
egonotto
 

Offline nctnico

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Re: RS RTM3K vs RTA4K
« Reply #18 on: March 01, 2021, 10:31:48 pm »

I thought it is not possible to measure error pk-pk and that is why it is always given in rms. Did you check the rms value, is it like in the spec in that case ?
Statistically speaking you can say that 99.7% of the values are within 3 times the standard deviation. So peak-peak should around 6 times the RMS value.

Also the R&S scopes use decimated data for math so it will help to set the memory length to a short span to force the oscilloscope to use raw data. I just did a test but I get the same results as egonotto has posted on the RTM3k I have here.
« Last Edit: March 01, 2021, 10:41:14 pm by nctnico »
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline metebalci

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Re: RS RTM3K vs RTA4K
« Reply #19 on: March 01, 2021, 10:41:12 pm »
Yes. I meant if one is looking for upper bound, it is problematic.
 

Offline metebalci

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Re: RS RTM3K vs RTA4K
« Reply #20 on: March 01, 2021, 10:51:43 pm »
I just did a test but I get the same results as egonotto has posted on the RTM3k I have here.

So this brings me back to my original question. There is an RS marketing video (RTM vs RTA, on youtube), which says RTA has a "significantly lower noise floor" than RTM, which I do not understand.
 

Offline tautech

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Re: RS RTM3K vs RTA4K
« Reply #21 on: March 01, 2021, 11:15:13 pm »
I just did a test but I get the same results as egonotto has posted on the RTM3k I have here.

So this brings me back to my original question. There is an RS marketing video (RTM vs RTA, on youtube), which says RTA has a "significantly lower noise floor" than RTM, which I do not understand.
Yes you have a bit of a dilemma wanting a low noise front end DSO and to do FRA to some 100+ MHz.
SDS2104X Plus could be a 2 birds with one stone solution although you still need a signal stimulus to 100+ MHz.

Not one instrument can do both beyond ~50 MHz which is the limit of SDS2104X Plus internal AWG.
Avid Rabid Hobbyist
 

Offline nctnico

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Re: RS RTM3K vs RTA4K
« Reply #22 on: March 01, 2021, 11:16:33 pm »
I just did a test but I get the same results as egonotto has posted on the RTM3k I have here.

So this brings me back to my original question. There is an RS marketing video (RTM vs RTA, on youtube), which says RTA has a "significantly lower noise floor" than RTM, which I do not understand.
I found the video and I call BS on the claim. The difference is that the noise floor isn't specified on the RTM3k and it is on the RTA4k.
There are small lies, big lies and then there is what is on the screen of your oscilloscope.
 

Offline egonotto

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Re: RS RTM3K vs RTA4K
« Reply #23 on: March 01, 2021, 11:24:19 pm »
Hello,

it seems that the noise floor from RTM and RTA  is equal.
It seems also that the mainboard in RTM and RTA are the same.

It exist documents for Instrument Security for RTM and RTA.
They both tell you that there are 4GB "Intermediate measurement
data" (sample memory) and 1GB "Operating system - Measurement control
data and measurement data"

Best regards
egonotto
 

Offline metebalci

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Re: RS RTM3K vs RTA4K
« Reply #24 on: March 01, 2021, 11:27:33 pm »
Yes you have a bit of a dilemma wanting a low noise front end DSO and to do FRA to some 100+ MHz.
SDS2104X Plus could be a 2 birds with one stone solution although you still need a signal stimulus to 100+ MHz.
Not one instrument can do both beyond ~50 MHz which is the limit of SDS2104X Plus internal AWG.

My question regarding to freq. response analysis on the other thread and the question on this thread is actually not very related :)
 


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