Frequency response of your DSO - Page 1
Forum section: electronics / testgear

author: tinhead
author_rank: Super Contributor
timestamp: January 29, 2013, 11:53:16 pm
content: while making some measurments for another one threadhttps://www.eevblog.com/forum/projects/transmission-line-avalanche-pulse-generator/i thoughtit could be nice to see the frequency response of other DSOson the market.I know, here and there other people posted already some pictures/results, but to have it in one thread could be more transparent.So if you, you or you have a (proper) equipment to run some measurments on your DSOs, please do it so and add the information here. You can use as well the attached excel file to add/compare with my result.Note: please don't use your DSO probes, unless you have some nice active probes and know what you doing. A RG-xxy cable from Signal Generator, terminated properly on the DSO end (this can be internal 50R termination, but as well t-connector with 50R at one end) should be the best option. Signal Gen should be something 1-200MHz at least, sine of course, when possible not one-hung-low type.EDIT: proper means at least known signal source with max. deviation < ±1dBm over the measure range. This should be good enough to have an compare and overview

author: Unknown
author_rank: Unknown
timestamp: January 30, 2013, 12:27:27 am
content: A few years ago, I posted the frequency response of an old Tek TDS-220 100 MHz lunch box DSO (though it lacks space for your lunch, unlike some cheap bench meters). I also compared the various vertical attenuator settings, this made a surprising amount of difference. I'll see if I can dig up the data later.I remember several people with access to decent RF equipment (eg. rf-loop) quoting -3 dB numbers for the Rigol DS1052/1102E, but I don't think they ever posted the actual frequency response.

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 30, 2013, 12:34:31 am
content: OT: since iirc i've raised this issue here and there without satisfactory reply... i have no proper equipment to test, so i had to find a workaround, first using diode and cap and then others and fancy diy software etc etc, now i have a way that makes the DSO freq respond is 'almost' irrelevant. i can plot my DUT freq responds without having to worry too much of this matter.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: January 30, 2013, 01:51:50 am
content: Hi Group,Here is the frequency response of my Tektronix TDS 754A 500 MHz scope.A HP8657B RF generator was used. The cable was a very quality Goreflex.I have also attached a zip file of the raw data if anybody wants you manipulate the data.Jay_Diddy_B

author: robrenz
author_rank: Super Contributor
timestamp: January 30, 2013, 02:46:22 am
content: Quote from: Mechatrommer on January 30, 2013, 12:34:31 amPlease tell us the details.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: January 30, 2013, 03:20:54 am
content: Hi,This time I measured a Tektronix 11A71 in a DSA602A mainframe. I could not get a stable waveform beyond 1.4 GHzThe setup was a HP 8657B signal generator and a Goreflex cable.I have attached a zip file with the measurements for anybody who wants manipulate the data.Jay_Diddy_B

author: Mechatrommer
author_rank: Super Contributor
timestamp: January 30, 2013, 03:36:52 am
content: Quote from: robrenz on January 30, 2013, 02:46:22 amoriginal message transferred to...https://www.eevblog.com/forum/projects/poor-man's-frequency-respond-cir-kiti dont want to hijack this thread. Cheers.

author: ve7xen
author_rank: Super Contributor
timestamp: February 01, 2013, 07:31:13 am
content: I have collected data using a Rigol DS2072 (70MHz) and HP 8657A signal generator (set for 1Vrms), connected with 1m of crappy RG-58 coax and a T with 50R termination. This generator is spec'd with flatness of +/- 0.5dB, but only at 0dBm, I'm running it here close to its max output of 17dBm. It's also probably not been calibrated in a long time, though I tuned it 6 months or so. I've somewhat 'guessed' at the RMS value for some of the readings, as the Rigol's RMS measurement can change 20-30mV depending on the horizontal scale. Not sure what that's about, but tried to get the most consistent values. All that to say this is not a very scientific survey.Don't use Excel, so I created my own sheet in Google Docs, which is sharedhereif you're interested in the raw data or prettier graphs.Edit: I was wondering if the dip at 30MHz was my generator/cabling or the scope itself, so I tried to measure it visually with my Tek 2230 analogue scope. By eye, it looks to be about 0.5dB down at 30MHz too, so I think this might be a measurement artifact.

author: tinhead
author_rank: Super Contributor
timestamp: February 01, 2013, 06:02:14 pm
content: Quote from: Wim13 on February 01, 2013, 03:36:26 pmtypical 16p, and thats good for 160-250MHz bw. The LPF in LMH6518 is doing the jobas well - and the software.Quote from: Wim13 on February 01, 2013, 03:36:26 pmi don't want to measure probes nor the input stage itself (because in todays designs with FIR filters the"input stage" ends up in DSP/FPGA), what the DSO is doing with the signal is also more complexand i wish to see the results "on screen" (read back with eyes/usb/gpib).However i don't want to ignore impendance match completly. Therefore the test signal should beterminated in the DSO with 50R, and in case of Rigol or other DSOs without internal 50R then simply externalywith 50R at the end of t-connector or feed through 50R temintor <- whatever works better for given DSO.

author: EV
author_rank: Frequent Contributor
timestamp: February 01, 2013, 06:25:07 pm
content: Quote from: Wim13 on February 01, 2013, 06:18:34 pmWhy not use the reading on the ascilloscope display, if we are testing scope?

author: tinhead
author_rank: Super Contributor
timestamp: February 01, 2013, 06:45:25 pm
content: Quote from: EV on February 01, 2013, 06:25:07 pmthis is exactly what i'm trying to achieve, to read values from display - manuall or usb/gpib/net/...A typical frontend frequency response would be not measured like that, but this is what i don't care aboutknowing that todays DSOs manipulating the data anyway.Example - my Tekway ST1202B is having Butterworth and not Gaussian respone (on display), where i know thatEXACT the same frontend is used by ATTEN/Siglent/Rigol - and from what i remember Rigol DS1k is having Gaussian response.I know additionally that the frontend itselt have no issue with up to 500MHz, and flat enough for 300-350MHz.I know however as well that due parallel connected ADCs (their capacity) the maximum frequency is cut, which iswhy Rigol never released DS1202E (10ADCs) but Tekway did (8ADCs).This thread should therefor show us what all these DSOs are having on display, to be able to compare implementationsand not pure hardware.

author: Marco
author_rank: Super Contributor
timestamp: February 01, 2013, 08:34:12 pm
content: Shouldn't you use a low impedance source and short cabling to test this? So impedance mismatch doesn't completely throw off your measurements? In fact a low impedance source and the original x10 probes seem a far better test than a 50 Ohm impedance source and a meter of coax to me.With 50 Ohm termination on the input my Owon will only have around 30 Ohm input impedance at 200 MHz...

author: Unknown
author_rank: Unknown
timestamp: February 01, 2013, 09:04:53 pm
content: Good luck finding a << 50 ohm leveled sine wave generator for 200 MHz. At 50 ohm source impedance, the voltage over the probe input will be 100% of the generator output at DC (1 MOhm impedance), and 50% of the generator output at 200 MHz (50 ohm impedance for a probe with 16 pF of capacitance). This will introduce a much larger error than the change from 50 to 30 Ohms.

author: Marco
author_rank: Super Contributor
timestamp: February 01, 2013, 09:37:29 pm
content: So use a buffer (active probe will do) or at least use a 10x or 100x compensated attenuator with nominally 50 Ohm input impedance instead of simple termination.Trying to gauge the quality of scopes not designed to have an accurate 50 Ohm input impedance over it's range with a 50 Ohm impedance source seems foolhardy to me ... is fine for the high end scopes with real 50 Ohm inputs, but not for the cheap DSOs. However unrealistic it is, they are designed for low impedance sources at high frequencies (of course even expensive passive probe scopes are the same in that respect).

author: tinhead
author_rank: Super Contributor
timestamp: February 02, 2013, 12:38:46 am
content: Quote from: Marco on February 01, 2013, 09:37:29 pmi did, and this didn't changed anything (as the probe need to be anyway terminated to 50R).I've tested some attenuators as well, no change.The only bad influence is when usind DSO own attenuator, everything without attanuator (max 200mV/DIV by x1) is fine.But that's fine, when using active probe with x10 2V/DIV are sufficient.Quote from: Marco on February 01, 2013, 09:37:29 pmdon't be so pessimistic, in china they using the same parts and same simulations, i don't think they stupid.Some trying to design own frontends (wasn't Owon SDS having already 3 different frontends?), others simplycopying proven design (Tekway/Rigol CA,E,D series/Agilent DSO1kB/ATTEN/Siglent/LeCroy WaveAce/...).But hey, you can run your own simulation of that China-most-used-frontend, schematic is herehttps://www.eevblog.com/forum/chat/hantek-tekway-dso-hack-get-200mhz-bw-for-free/?action=dlattach;attach=12233I ran my and i think it's not bad at all. I've added as well relais (worst case) parasitic capacitance (3p instead of 1p a in datasheet).

author: Marco
author_rank: Super Contributor
timestamp: February 02, 2013, 01:49:19 am
content: Quote from: tinhead on February 02, 2013, 12:38:46 amWith a buffer I mean either a buffer at the scope connector OR a buffer at the signal generator so you can just use the scope's own compensated 10x probe.QuoteAn attenuator in and of itself does little, but attenuation gives you room for compensation. I agree though, active probes won't help ... I thought for sure they'd be better designed, but looking at something like the P6012 all it does is add inline termination for high impedance scopes ... bleh.QuoteI'm not pessimistic, I'm just cognizant of the fact that they are designed for very low impedance sources at high frequencies and a compensated probe to get the correct frequency response. A cheap scope simply can't be tested as a separate system from it's probe unless you are willing to build specialized circuitry, inline termination is not the same as having an input designed to have 50 Ohm impedance over the device's usable frequency range ... the probe and it's compensation are integral parts of what makes up the frequency response.

author: tinhead
author_rank: Super Contributor
timestamp: February 02, 2013, 02:27:44 am
content: Quote from: Marco on February 02, 2013, 01:49:19 amwhat's about this one? LeCroy, 1M/50R input, 300MHz BWhttp://teledynelecroy.com/oscilloscope/oscilloscopemodel.aspx?modelid=2122#spec

author: Marco
author_rank: Super Contributor
timestamp: February 02, 2013, 02:59:56 am
content: What about it? It has internal termination, so you don't need inline termination ... as for whether it's designed to be 50 Ohm across it's rated bandwidth I have no idea, you'd hope so for a LeCroy (the limited voltage range for 50 Ohm does suggest it).

author: tinhead
author_rank: Super Contributor
timestamp: February 02, 2013, 03:20:35 am
content: Quote from: Marco on February 02, 2013, 02:59:56 amMarco,and that's exact the point, this scope is using exact the same frontend as Tekway/Rigol CA,E,D/Agilent DSO1kB/ATTEN/Siglent,an frontend designed to be used as 1M/50R. The only diff is that models with internal termination are using 49.9R resistor directnear BNC, which is from signal path perspective equal to feed through terminator.Therefor statement likeQuote from: Marco on February 01, 2013, 09:37:29 pmis simply useless, you can't judge about things you don't know.

author: Marco
author_rank: Super Contributor
timestamp: February 02, 2013, 03:40:17 am
content: Quote from: tinhead on February 02, 2013, 03:20:35 amJudging a scope which has a specified 50 Ohm input on the quality of that input is meaningful ... if it's not actually ~50 Ohm across it's frequency range that's a black mark on them.Judging a scope which doesn't have a 50 Ohm input on it's frequency response to a 50 Ohm source with an inline terminator for which it was never designed is not meaningful ... if you pretend that's doing anything more than performing a roundabout measurement of input capacitance that's on you.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 02, 2013, 04:07:04 am
content: imho. the Jim Williams' quote comes to mind."the best probe is no probe". if you somehow can bring the generator as close as possible to the point less than reflection length, you can connect them without termination on the dso input end. but whats the point? it may not be feasible bringing tonnes of equipment close together. a quality 50ohm coax and a quality inline terminator is all you need to get the "exact half" of the generator's signal appearing at the scope's input. as someone (Janne) proved, good (flat) to few GHz range (i believe it should be herehttps://www.eevblog.com/forum/beginners/how-to-better-wire-the-bnc-connector-and-ghz-issue/msg37963/#msg37963but the proof has been erased)

author: Marco
author_rank: Super Contributor
timestamp: February 02, 2013, 04:21:18 am
content: A quality inline terminator with a parallel 10 pF capacitor is no longer a quality inline terminator.

author: tinhead
author_rank: Super Contributor
timestamp: February 02, 2013, 01:26:32 pm
content: Marco,i see you still didn't got what the reason for this thread is. Ok, i will try once again. It does not matter WHAT an unknownideal scope, with calibrated 50R internal input is showing at rated XXX frequency - because we know this anyway frommanufacturer datasheet. The same for unknown DSO with provided probes, they almost always too cheap, they dohave almost always unknow frequency response, they didn't always matching the DSO, not always properly compensated.And here is the point, having signal source with known level at specific Z we can measure what a DSO, with no calibratedinternal 50R temrination, is doing with this signal. For why? Well, this is the reference level (and this is exactly what you using,not an imaginary or real value on input but what on display), a 50R teminator will be always 50R terminator, coax cable still acoax cable (and yes there are diff, but they didn't matter on "almost DC").And this is reference level for all DSOs then, no matter if they calibrated to 50R initernal termination or not, e.g. product A (Rigol DS1052E) will have on paper (from hardware point of view) exact the same response as product B (Agilent DS1052B).Why ? Becuse they using exact the same hardware. The questions is, due the fact that the software might be different, are the result on screen equal as well? And same apply to majority of chinese (and as well LeCroy, Agilent low end) products.For you, as owner of Owon, the kind of measurment is still important. You was looking for active probe, which would be thenanyway terminated external with 50R. So for you as well would be interessting to see what such probe, giving on product A suchrespone (with external termination) or product B (with internal calibrated termiantion) another response, is doing on your DSO.Btw, consider these active probe, i'm using two of them and the performance (up to ~500MHz) as as good as P6243(i'm cheating my TEK with own eeprom):http://welecw2000a.sourceforge.net/docs/Hardware/Aktiver_Tastkopf_mit_OPA659.pdfAnother aspect of this thread was to show kind of response, is it flat or gaussian? And here does not matter if you at DSOrated frequency off by 1.8dB (as my test DSO), the kind of response is still the same:

author: Wim13
author_rank: Frequent Contributor
timestamp: February 02, 2013, 01:39:25 pm
content: Back to the topic, to compare the graphs of different DSO's,If you want to compare you have to use everytime the same setup,and thats the point i want to make, otherwise its compare has no meaning.If a use a constant voltage on my DSO ( Rigol 2072 ) of 0 dbM ( 0,223 V )on the BNC connector, 1 Mohm 16 pf, i have a straight line from 70 Mhz 0 dB to 200 Mhz -3 dB.if a use a quality signal generator, 50 ohm, 1 meter of coax, T connector on the DSO with 50 ohmterminator with a kown specification i get a straight line form 70 Mhz 0 db to 200 Mhz -6 dB.Thats is making the difference.The uncertainty of this whole setup is within 1 db.If everyboy is using this samen setup, and also specify the uncertainy, then we can use all the info

author: Marco
author_rank: Super Contributor
timestamp: February 02, 2013, 01:50:12 pm
content: Quote from: tinhead on February 02, 2013, 01:26:32 pmI kinda assumed an active probe designed for high impedance scopes either put a buffer on the scope side connection or put a 10x compensated attenuator at the scope side which should get you close to a much more bearable 1 pF in parallel with the terminator, that's how I would do it.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 03, 2013, 01:44:34 am
content: Quote from: Wim13 on February 02, 2013, 01:39:25 pmif i understand you correctly... no. you'll get 70 Mhz-3dBdb to 200 Mhz -6 dB. it doesnt make any difference in the profile curve, everything are just moved 3dB down in every spectrum. and T connector with a dicky 50ohm terminator may not be as good as an inline (pass through) terminator. you may refer to the thread about "coax and bnc"...https://www.eevblog.com/forum/beginners/how-to-better-wire-the-bnc-connector-and-ghz-issue/and read the whole story...attenuators. but you also can find such similar enclosured terminator. i've modified one such attenuator (because its reachable from ebay, not quite cheap though compared to the T+50ohm dicky) to get a "conceptually" better terminator. i'm not sure though if an attenuator can be used (as is) in place of a terminator.an active probe is only more usefull if you dont have such low impedance (50ohm) generator and source loading is an issue. a properly terminated coax is as good or better than active probe, that has been the standard setup (with robust generator). experts are using this method unarguably. end of story... imho.@Marco: i'll consider a DSO as a black box i dont have to think about its internal (parallel) capacitance. everything in the front end input are considered "lumped" (black box). all i care is a signal feed into it and what it shows on the screen. during real life we dont want to be bothered with this 15pF internal capacitance issue "everytime", all we care is whats on the screen and how accurate it is compared to what is actually feed into it.

author: Wim13
author_rank: Frequent Contributor
timestamp: February 03, 2013, 01:06:27 pm
content: Oke , here is the result of the Rigol 2072 DSO, graph is made with signal of -10 dBm ( 70 mV ) input on BNC.Measure point every 10 Mhz, used read out of the rms value on the DSO.The differences between channel A and B are within 0.5 db, so no use to plot.

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 03, 2013, 02:14:00 pm
content: Quote from: ve7xen on February 01, 2013, 07:31:13 amsince Win13 profile differs from ve7xen esp at -3dB point (~180MHz vs ~100MHz)... the 30MHz notch is probably from your "not so good" coax setup? i dont know. do you have discontinuity of the shielding? have you changed the cable and/or terminator and retry the test? have you tested using 0dBm instead of the maxed 17dBm? i believe providing the image of the test setup will give a better idea if the test result is sound or not.but i like the idea of profiling both channel, we can see the mismatch level.

author: grumpydoc
author_rank: Super Contributor
timestamp: February 03, 2013, 02:40:59 pm
content: Interesting - must find time to graph out the Lecroy.Don't forget that past 3-400Mhz the cable and BNC's will start to have a significant loss of their own, 1 metre of RG58 has a loss of 0.36dB at 400Mhz rising to 0.7dB at 1GHz and I found a datasheet for "mil spec" BNCs which gives the insertion loss as 0.1 SQRT(BW in GHz) so 2 BNC's plus 1m of coax is almost 1dB down at 1GHz

author: tinhead
author_rank: Super Contributor
timestamp: February 03, 2013, 03:06:36 pm
content: right, but as everybody is anyway using something 0.5 and 1m of coax we can ignore it as "common loss".

author: grumpydoc
author_rank: Super Contributor
timestamp: February 03, 2013, 03:28:54 pm
content: QuoteOK, if that's the aim but less good for trying to make absolute measurements - which is why high frequency levelled sine wave generators have a level sensing head to eliminate cable losses - at least things like the Tek SG504 and SG5030 do - I presume others (still?) do this.

author: Jay_Diddy_B
author_rank: Super Contributor
timestamp: February 03, 2013, 04:39:51 pm
content: Hi,I think the reason that Tektronix used levelling heads is that the inputs on the scopes have some mismatches. The VSWR of the 7A29 is specified at 1.2 : 1 That is an impedance of 42 to 60 Ohms.By using a levelling head the effect of the mismatch is minimised.The 50 Ohm only scopes are a lot better in this regards than the 1M / 50 ohm scopes. These switch a 50 Ohm termination in parallel with the 1M input and have high impedance attenuators.The 50 Ohms only scopes use 50 Ohm attenuators and are lot better. There is a thread which shows the internal construction of the 7A29 attenuator.https://www.eevblog.com/forum/reviews/tektronix-7a29-teardown/msg188496/#msg188496The SG503 50kHz to 250 MHz calibration generator did not have a levelling head.Jay_Diddy_B

author: grumpydoc
author_rank: Super Contributor
timestamp: February 03, 2013, 05:12:40 pm
content: QuoteHadn't particularly thought about that I confess.But I think that >500Mhz levelled sources need to eliminate the cable loss regardless- the SG504 is specified as flat to 4% (0.34dB). 1m of RG58 is about the same drop at 400Mhz and more (about 8.5%) at 1GHz so having a sensing head makes sense to keep in spec anyway.Not sure whether the SG504 actually used RG58 to the head though.QuoteTrue but cable loss is less of a problem for the SG503 as it only goes up to 250MHz where 1m of RG58 has a loss of about 0.25dB

author: rf-loop
author_rank: Super Contributor
timestamp: February 03, 2013, 06:03:30 pm
content: Here just OP asked displayed response.Sweep 100s, start 1MHz stop 200MHz, linear.Owon acquire mode is peak.Signal generator, HP8644B flatness measured before test only directly from output N-connector so that there was only HP8482H connected directly to generator N-connector, meter used HP437BI did not find between 1MHz to 200MHz more than +-0.03dB if set 1MHz level as 0 reference.Real flatness not measured in test configuration. (I have no realiable tools for this).Test system reactive load together with cable can do whatever... but for this purpose this accuracy is ok imho. Also, this is just how we many times use scope in practice.

author: tinhead
author_rank: Super Contributor
timestamp: February 10, 2013, 01:37:03 pm
content: small update : this is what collected so far, look below.still looking for other ppl/DSO data

author: Mechatrommer
author_rank: Super Contributor
timestamp: February 10, 2013, 02:55:15 pm
content: at last! i get the chance to see the ds1102e (ds1052e) respond with greater resolution (still no xls yet?) thanks tinman for the report. otoh, tekway tried to overcompensate (peaking) their dso to get higher bw.

author: tinhead
author_rank: Super Contributor
timestamp: February 10, 2013, 04:10:35 pm
content: Quote from: Mechatrommer on February 10, 2013, 02:55:15 pmactually no, the first part of frontend (up to AD8370) is not using (in my test setup) the attenuator nor compensation circuit.The measured response is combination of :- this part of frontend- the 20MHz bw filter and it's influence even if off- the LM6552 output termination- amount of parallel connected ADCs- parasitics-softwareWhen you compare to Rigol DS1000E, the first part of frontend is same, 20MHz filter similar (this is part which does have influense of the total response and partially on the bw),LM6552 termination same, amount of ADCs diferent (which is why Rigol was not able to produce 200MHz DSO with these ADCs, this is why they useddifferent ADC in CA models) and software as well different (whih is for these DSOs a big difference - on Tekway i can move the -16dB point between 60MHz and 999MHz,where of course usefull is something below nyquist frequency).The result is flat response in compare to Rigols combination of flat and gaussian response. The "overcompensation" is typical for butterworth response, so nothing wrong here.For gaussian DSO, such response would be however really overcompensated input.

author: EV
author_rank: Frequent Contributor
timestamp: February 14, 2013, 09:08:46 am
content: Rigol DS2202Generator HP8642A connected with BNC cable and feed thru 50 ohm terminator.Output voltage 100mV.Attached picture and exel file

author: EV
author_rank: Frequent Contributor
timestamp: February 14, 2013, 12:15:41 pm
content: Tektronix TDS 30321.Generator HP8642AConnected with BNC cable to 50 ohm input of the scope.Output voltage is 100mV.2.Generator HP8642A terminated with 50 ohm feed thru terminator.This terminator is connected with with Fet probe P6243 to 50 ohm input of the scope.Output voltage is 100mV.3.Generator HP8642A terminated with 50 ohm feed thru terminator.This terminator is connected with with Fet probe P6205 to 50 ohm input of the scope.Output voltage is 100mV.Picture attached.

author: grumpydoc
author_rank: Super Contributor
timestamp: February 14, 2013, 08:50:49 pm
content: Finally had chance to graph out the Lecroy 9354TM - this is specified as 500Mhz bandwidth with the internal 50ohm terminator.Signal generator was a Marconi 2024, 1m RG58 coax, 0dBm signal level, internal 50ohm termination. The signal generator is supposed to be flat to 1dB or so but I don't really have anything accurate enough to check much past 10kHz so I'm rather trusting it blindly.Almost spooky that the graph shows the -3dB point as exactly 500MHz - though as previously discussed the cable & BNCs are probably contributing about half a dB by 500MHz. Interesting peak at 200Mhz - not sure why that is unless the front end has been artificially tweaked to hit the 500MHz bandwidth. Could be the Marconi, of course.

author: JoeyP
author_rank: Frequent Contributor
timestamp: February 14, 2013, 09:36:30 pm
content: Quote from: grumpydoc on February 14, 2013, 08:50:49 pm1m of RG58 has a propagation delay of 5nS, which happens to be the period of a 200MHz signal. The peak may indicate a mismatch at the scope input and/or Marconi output. Note there's also a dip at 100MHz. The Marconi probably has 10dB of attenuation inserted in its output path at 0dBm output level setting, which should provide a fairly accurate source impedance (unless it's damaged). I would bet the mismatch is at the scope. This wouldn't be surprising since the 50 ohm terminations in most scopes don't have great return loss specs.

author: grumpydoc
author_rank: Super Contributor
timestamp: February 14, 2013, 09:56:35 pm
content: QuoteOK, hadn't thought of that, interesting.Not sure whether I should be pleased that I found it or miffed that it's there. It's all within ±0.5dB though up to about 225MHz so not the end of the world.I'd assumed that the dip at 100MHz was the start of being able to demonstrate the roll-off, if you ignore the 200MHz peak it looks like it would roll smoothly from 0.5dB down at 100 to 1dB down at about 250 and 2dB down at 350MHz.I might map out the other inputs and also the other Lecroy that I have (a 9354T). It could also be useful to try with a 50ohm terminator on a BNC-T piece and compare with the 'scope's termination.I confess that, although I have a sort of basic grasp of what's going on as soon as we get into the detail or the maths it goes over my head.

author: JoeyP
author_rank: Frequent Contributor
timestamp: February 14, 2013, 10:36:52 pm
content: If you have a 10dB BNC attenuator pad, it would be very interesting to bump the Marconi up to +10dBm, insert the pad directly at the scope input, and do the same plot. If the peak doesn't go away, move the pad to the Marconi's output instead, and repeat the test. If the peak goes away in either condition, it was due to impedance mismatch/reflections. If not, it's part of the scope's response.

author: grumpydoc
author_rank: Super Contributor
timestamp: February 14, 2013, 10:41:31 pm
content: QuoteI don't but think I might keep my eye out for one.The Marconi has the high (+25dBm, I think) output option BTW so the 0dBm output might be more than a 10dB attenuator.

author: JoeyP
author_rank: Frequent Contributor
timestamp: February 14, 2013, 10:51:45 pm
content: I'd be surprised of the mismatch was at the Marconi end - particularly since its range is much higher than the scope's BW. I only included that possibility in case it happened to be damaged. If its output level is correct, then its attenuator is probably OK.

author: nctnico
author_rank: Super Contributor
timestamp: February 15, 2013, 02:51:59 am
content: AFAIK this kind of peaking is pretty normal (it is well within 1dB BTW). If they add a filter which peaks a little bit they can squeeze an extra 10% bandwidth out of the same hardware.

author: Someone
author_rank: Super Contributor
timestamp: February 15, 2013, 06:49:50 am
content: Plotted out the response and input VSWR for one of the MSO-X 3104A units we have kicking about, if I find some time I'll do one of the 200MHz units or some of the Lecroy hardware.Measured out to 990MHz with a HP 8656B as the source, then used a N9923A out from 1000MHz and for the VSWR. All uncalibrated and I couldnt be bothered dragging out the thermal power meter to track down the reason for that 1dB drift in the result.

author: grumpydoc
author_rank: Super Contributor
timestamp: February 15, 2013, 08:20:23 am
content: QuoteI have no reason to suspect a problem with the Marconi attenuator - certainly at lower frequencies it appears to be spot on. The graph 0dB line is pretty close to 0dBm - I chose the 50kHz reading as the reference point. The 'scope reading for that was 221.8mV rms which is about -0.07dBm (unless both are off by the same amount, of course).I do have a Marconi 2305 which I bought to adjust a 2022 which had lost it's RF level cal due to an EEPROM failure - not got round to that project yet so I've not fired up the 2305 but it was bought as working. I might use its RF level meter to check the Marconi output although I think the accuracy is only supposed to be +/- 1dB - maybe not enough to confirm that peak but it should show whether the Marconi is broadly flat in the 100MHz-500Mhz band.

author: The Electrician
author_rank: Frequent Contributor
timestamp: February 15, 2013, 10:50:46 am
content: Here are some measurements I made of various impedances over a 0-1GHz frequency range, and the frequency response of an Agilent DSO5034 300 MHz scope.First, here's the Smith chart plot (0-1GHz) of the 50 ohm calibration load after calibrating the network analyzer. You can just barely see the yellow dot right at the center of the zoomed in Smith chart:Next, here's the impedance at one end of a 1 meter cable with the calibration load at the other end. This is a precision 1 meter, armored, expensive reference cable. Notice that the impedance is very nearly 50 ohms over the whole frequency range:Here's the impedance at one end of a 53 cm piece of RG-58, average quality, calibration load at the other end, with commercially installed BNC connectors on the ends:This VNA is a portable unit and it's possible to get the VNA port close enough to the scope input connector to make measurements of the scope input impedance without using a cable, but rather a simple BNC adapter between the VNA and the scope. Here's the impedance of the scope input, with the input impedance selected to be 50 ohms, swept from 0 to 1 GHZ:Here's the input impedance of the scope with its input impedance set to 1 megohm and with a 50 ohm pass through inline:Here's the frequency response of the scope (input impedance set to 50 ohms) without using a cable between the signal generator and the scope. I was able to get the generator output connector close enough to the scope to do the same trick I did with the VNA. There's only a single BNC-BNC adapter between the generator and scope:

author: ivan747
author_rank: Super Contributor
timestamp: February 15, 2013, 10:56:08 am
content: Does anybody know where I can build a simple adjustable 10-20MHz sine wave oscillator to test the cheaper scopes like the Velleman HPS-10? Thanks.

author: Wim13
author_rank: Frequent Contributor
timestamp: February 15, 2013, 06:26:01 pm
content: @ The Electrician,Thanks for this measurement and very nice pictures... very intresting, and explained a lot.......

author: JoeyP
author_rank: Frequent Contributor
timestamp: February 15, 2013, 08:02:56 pm
content: Quote from: grumpydoc on February 15, 2013, 08:20:23 amIt dawned on me that there is an easier way to determine whether reflections are the cause. You could simply make the measurement with a different cable length. If the peak moves, it's due to impedance mismatch, if not, it's part of the scope's response.

author: DrBob
author_rank: Contributor
timestamp: March 29, 2013, 06:47:43 am
content: One of the ways you can estimate the frequency response (-3 dB Bandwidth = BW) of a DSO, is to measure the rise time or a very fast rise time pulse and use the formula:BW ~= 350/Trwhere Tr is the measured rise time of the pulse.So we would expect the rise time of the DS2 series to be:Scope BW MHz ~Rise TimeDS2072 70 5.0nsDS2102 100 3.5nsDS2202 200 1.75nsThe rise time of the test pulse should be less than 20% of the Tr of the scope to create less than about 2% error. The problem for many, is where to find an appropriately fast rise pulse to apply to the oscilloscope.The relatively slow rise time calibrator pulse, which is only intended to calibrate amplitude, is entirely unsuitable for Tr measurements. Fortunately, the Rigol DS Series has a trigger out pulse available on the rear panel that can serve moderately well if you do not have access to something faster.Lets look at it.To minimize the cable reflections, the 42" 50 ohm good commercial coaxial cable transferring the pulse to the measuring scope was terminated with a good quality 50 ohm feedthru, like the Rigol PL-50, if the scope does not have a 50 ohm input option - like the Rigol DS Series.My measurements of the trigger out pulse were done on a 1990s vintage, but still very functional, Tektronix 7904A using a Tr=25ps (0.025ns) type S-4 head in a 7S12 sampling plugin (photo 1). It's accuracy was affirmed by measuring a Tektronix S-2 25 ps pulse generator head correctly. A BNC to SMA adapter and 10dB attenuator was used at the sampling head to reduce the DS2202's trigger voltage.Since it is an analog scope, we have to do some things the old fashion way. The input signal is set to be 5 divisions high and the time to transverse the center 4 vertical divisions (10% to 90%) is the rise time. The accompanying photo shows this is 1.0ns (photo 2) through the 42" BNC cable. A 50 ohm feedthru is not necessary, as the input impedance of the sampling head is 50 ohms.An additional measurement using a military quality 9" BNC cable gave 0.9ns for the pulse rise time - but that cable is too short to reach from the rear output to the DS scope's input.So there we have it - a readily available moderately fast rise time pulse for Rigol DS Series users. It would be much better if it were, say 0.3ns, but we will see there is a way to compensate for it and calculate the true rise time of a scope with a bandwidth into the 200 MHz region.Measuring a scope's BW using risetime, in my opinion, is not the best way. But scopes measure pulses as well as sine waves, so knowing your scope's risetime is a very good thing.

author: EV
author_rank: Frequent Contributor
timestamp: March 29, 2013, 07:59:34 am
content: Quote from: DrBob on March 29, 2013, 06:47:43 amI have also measured this Rigol DS2202 trigger out rise time. I used Tektronix TDS3032 scope with FET Probe P6243 and 50 ohm feed thru terminator between trigger out BNC connector and probe tip.Rise time is 848 ps. Look at the attached picture. This TDS3032 is fastest scope I have.

author: DrBob
author_rank: Contributor
timestamp: March 29, 2013, 05:09:04 pm
content: Quote from: EV on March 29, 2013, 07:59:34 amGood technique and nice work with a 500 MHz DSO. That agrees well with my ~900ps measurement at the end of a 9" cable.

author: EV
author_rank: Frequent Contributor
timestamp: March 29, 2013, 05:37:56 pm
content: Quote from: DrBob on March 29, 2013, 05:09:04 pmIt is a 300 MHz scope. However measured BW (-3dB) with RG58 cable is about 410 MHz and with FET probe P6243 BW is over 500 MHz. Look at earlier post:https://www.eevblog.com/forum/testgear/frequency-response-of-your-dso/msg192342/#msg192342

author: tinhead
author_rank: Super Contributor
timestamp: March 29, 2013, 05:47:23 pm
content: Quote from: DrBob on March 29, 2013, 06:47:43 ambut only on scopes with gaussian response, on flat-type response DSOs we need to use 0.4 to 0.5 instead of 0.35.And even 0.35 is only truth when the response is real gaussian, today you can get an (not only chinese) DSO withmixed response, where the first part is coming from e.g. input stage and the second part of the response(e.g. butterworth fir) is coming from the digital part of DSO.So yes, rise time can be used to measure bandwidth but only WHEN you exactly know the frequency response of your DSO,which is what i trying to achieve in this thread.

author: DrBob
author_rank: Contributor
timestamp: March 29, 2013, 06:47:09 pm
content: Quote from: tinhead on March 29, 2013, 05:47:23 pmYes - that formula only applies to a gaussian response front end. I will soon show how well it applies to the DS2202.I have just one more follow-up post on making rise time measurements, then I will get to real meat on the bone and the main thrust of the tread - measuring BW:1. The old fashion way,2. A newer way,3. The newest automated way

author: dougg
author_rank: Regular Contributor
timestamp: March 29, 2013, 07:08:22 pm
content: Quote from: EV on March 29, 2013, 07:59:34 amWhen I measured the same thing (DS2202's trig out with another Rigol (DSO1024A)) the waiting to be triggered voltage level was around 0 volts and the triggered voltage level was around 3.3 volts. The DS2000 specs don't say what the trig out can drive so I did not try a 50 ohm termination.

author: eurofox
author_rank: Unknown
timestamp: January 02, 2014, 01:42:44 pm
content: Hi,Here is the graph from my TDS784D, basicaly 1GHz scope but trigger til 1,9 Ghzeurofox

author: Carrington
author_rank: Super Contributor
timestamp: January 02, 2014, 04:45:50 pm
content: Quote from: tinhead on February 10, 2013, 01:37:03 pmWhat does DS2072_1st and DS2072_2nd mean?By the way, the Tekway DTS1202B's input stage is very similar to that used in the DS2072. [J1=U6, Q1=R2W (HW1.0) and Q3=Q2=1B].Unfortunately still undetermined some values and connections for the DS2072's input stage.So, if someone already dismantled their DS2072A and want to collaborate these are some of the connections to be determined (Red circles).And also would be interesting to know C and R values (without marking code), but perhaps this, is asking too much, because must be unsoldered.Quote from: tinhead on March 29, 2013, 05:47:23 pmQuote from: DrBob on March 29, 2013, 06:47:09 pmHow we classify the response for the DS2000? The theory say this:https://www.eevblog.com/forum/testgear/sniffing-the-rigol%27s-internal-i2c-bus/?action=dlattach;attach=73448

author: tinhead
author_rank: Super Contributor
timestamp: January 02, 2014, 06:18:34 pm
content: Quote from: eurofox on January 02, 2014, 01:42:44 pmthis is crazy, i always loved TDS7xx series (even if the f* loud)

author: tinhead
author_rank: Super Contributor
timestamp: January 02, 2014, 06:28:26 pm
content: Quote from: Carrington on January 02, 2014, 04:45:50 pmthat measurment results from two persons.Quote from: Carrington on January 02, 2014, 04:45:50 pmit is actually that way:DS2000 does have similar frontend to TekwayTekway does have similar frontend to DS1000EDS1000E does have similar frontend to DS1000CADS1000CA does have similar frontend to DS1000B (i think)DS1000B and Instek (don't remember the name) they have similar frontend ^^... and between all that point you can add the other manufacturers, as they copied it as well,where Siglent added e.g. 50R termination without clamp diodes but Rigol added some, etc.Quote from: Carrington on January 02, 2014, 04:45:50 pmkind of mixed response, where the first part is gaussian and then fallsing rapidly down as known from flat response (especially when 300MHz enabled). For the bandwidth is however the first part responsible (as it goes far below -3dB), the rest is let's call it a better low pass

author: Carrington
author_rank: Super Contributor
timestamp: January 02, 2014, 06:44:34 pm
content: Quote from: tinhead on January 02, 2014, 06:28:26 pmOK.Quote from: tinhead on January 02, 2014, 06:28:26 pmLOL...Quote from: tinhead on January 02, 2014, 06:28:26 pmSo, better measure the BW using the traditional method (-3dB).Thanks.

author: eurofox
author_rank: Unknown
timestamp: January 02, 2014, 07:34:49 pm
content: Quote from: tinhead on January 02, 2014, 06:18:34 pmYes it is quite impressive and I would like to add that BNC cable and connectors have normaly a bandwith limited to 1Ghz and I'm sure that many DB's are lost this way in the test above 1Ghz.

author: Altemir
author_rank: Contributor
timestamp: January 02, 2014, 07:39:51 pm
content: Some mesuarements from our lab... Sorry for my bad english and quality of Hi-freq mesuarements. I have used Hoden HB-B100 BNC-BNC cable, R&S SMB100A (2.2GHz), Tektronix 011-0049-02 Feed-through Terminator (only for 1M inputs scopes and "50Ext", for other - internal 50 Ohm load). Level of signal was 1Vrms at all experiments. Memory depth for MSO4024 was AUTO.

author: tinhead
author_rank: Super Contributor
timestamp: January 02, 2014, 08:12:33 pm
content: Quote from: Altemir on January 02, 2014, 07:39:51 pmthank you very much!

author: DL8RI
author_rank: Regular Contributor
timestamp: January 02, 2014, 11:00:58 pm
content: Here some values of an erm... "elderly" DSO, the Philips PM3320A, Specified 200MHz BW and 250MS/s.My source is a Rohde & Schwarz SMS, the VSWR was done with an R&S ESVP with an HP 8502A Opt H26 Reflection Test-Set.I've done the measurement until the scope showed no reasonable waveform anymore, so it's far beyond the 200MHz. The Input was set to 50 Ohm, no additional Attenuator was used, input-Power 0dBm.Next week (or somewhat later) my Hantek hand-held Scope should arrive, I will post the results. They may be more interesting.

author: babysitter
author_rank: Frequent Contributor
timestamp: January 16, 2014, 11:12:34 pm
content: Although not yet the requested response measurement, I used a antenna analyzer FA-VA3 to check for the matching of diverse scopes with either a picoscope feedtrhough terminator (my own) or a pomona 4119 (workplace).This ZIP contains the CSV tables with the real/imaginary part of the impedance seen by the analyzer using the pomona terminator. Similar data will follow for my home scope(s).Unfortunately, I set the cable compensation to UT-141 semirigid cable by accident but hey, I think you can live with it !The filenames tell about the scope settings, as the matching usually changes with the V/DIV Setting, not every setting but changes in ranges over several settings. The settings are selected to represent different cases.Expect me to post data for the picoscope terminator for the above scopes and my own VC 630-2, TEK 453 and DST1062B/200 MHz hacked later, and RF response as soon as I fixed my Marconi 2018A or decided to run it unrepaired (lost FM and PM ability, maybe some latch/multiplexer issue...), otherwise the FA-VA3 will be used as source.EDIT: Baby 2 has shown up a bit early, further work postponed !

author: Co6aka
author_rank: Unknown
timestamp: January 17, 2014, 12:15:08 am
content: Quote from: eurofox on January 02, 2014, 07:34:49 pmThat depends upon materials and construction. I rescued some rather strange and wonderful Huber-Suhner cables from a scrap bin; the cable is marked "6GHz" and the connectors are silver plated with gold plated pins. I tested them all at 3GHz when I got them, but don't recall the loss per foot. Regardless, for accurate measurements you must sweep your cables and make up an attenuation profile, and then offset your device-test measurements accordingly.When I measured the frequency response of my DS4014-with-hacked-FW, I first measured the generator-plus-cables into the RF power meter, and then adjusted the generator to produce as close to 0dbm as I could get. (The smallest amplitude step of the Agilent E4438C is 0.2dbm so that was the limiting factor.) The E4438C had been calibrated in August, and the MiniCircuits power meter had just been calibrated a couple of weeks before, so I "trusted" it most, but both were in close agreement. Anyway, the cable and connector losses were quite low, even at 1GHz, which was the upper limit of my DS4014 tests.If you have access to some RF test EQ then you can make up loss profiles for all of your cables and adaptors -- label 'em first, otherwise...

author: Altemir
author_rank: Contributor
timestamp: January 19, 2014, 04:28:43 pm
content: New corrected results, that I have put in my topic.

author: rfbroadband
author_rank: Unknown
timestamp: January 25, 2014, 06:20:42 am
content: R&S RTO 1044

author: Neganur
author_rank: Unknown
timestamp: April 17, 2014, 01:12:07 pm
content: I'll see if I can do a frequency response measurement on the MSO-X3104 later. Unfortunately, I know that the output of my HP8648B signal generator isn't constant over the whole frequency range, and I don't know its flatness either. The measurement report claims that the scope is at - 1.00 dB at 1 GHz with 0.29 dB uncertainty.I was testing the Vince/Williams pulser on it and was a bit surprised that I get nowhere near the bandwidth I should be getting (0.23/330 ps = 700 MHz). According to the measurement Vince did, the pulser has approximately 200 ps rise time.

author: jpb
author_rank: Super Contributor
timestamp: April 17, 2014, 01:55:10 pm
content: Quote from: Neganur on April 17, 2014, 01:12:07 pmThe 0.23 constant is based on a single pole filter and 20-80% rise time (more common is the 0.35 relating to single pole and 10-90% rise time). According to various app notes from Tektronix and Agilent for higher frequency scopes with maximally flat pass bands the constant can rise from 0.35 to 0.4 or even 0.5 so this could account for some of it. If you multiply 0.23 by (0.5/0.35) you get around 0.32 and the bandwidth rises to much nearer 1GHz.(I think that the 0.23 should actually be 0.22 for a single pole - ln(0.8/0.2)/2.pi = ln(4)/2.pi=0.22.The Agilent spec sheet is for a 10-90% rise time of 450psecs giving the product as 0.45.It might make more sense to work with 10-90% rise times and compare that with Agilent's spec. directly.

author: EV
author_rank: Frequent Contributor
timestamp: April 17, 2014, 02:03:53 pm
content: Quote from: Neganur on April 17, 2014, 01:12:07 pmHere is my test with this pulser. According to Vince the its rise time is 190 ps. I used TEK R7103 scope. Its BW is 1 GHz. I get rise time 10-90% to about 400 ps. It gives BW= 0.350 / 400 = 875 MHz. I have attached pictures with time base 1 ns, 500 ps and 200 ps about the pulse. The pulser is connected with 20 dB attenuator to the scope.

author: EV
author_rank: Frequent Contributor
timestamp: April 17, 2014, 02:14:41 pm
content: Maybe the risetime can be corrected as follows: Rt^2 = 400^2 -190^2 and Rt = 352 ps.Then BW is 350 / 352 = 994 MHz.

author: Neganur
author_rank: Unknown
timestamp: April 17, 2014, 02:18:04 pm
content: Quote from: jpb on April 17, 2014, 01:55:10 pmYou're right, the datasheet lists 1 GHz BW with a calculated 10%-90% rise time of ~450 ns, so that would not be Gaussian. The user manual manual however, mentions the Gaussian response of 0.35/f_BW for 10%-90% so maybe the manual is wrong.I did more tests with a Tek 284 Pulse generator (t_rise = 70 ps) and get figures closer to the claimed numbers in the datasheet t_r(10-90) ca. 413 ps.

author: jpb
author_rank: Super Contributor
timestamp: April 17, 2014, 02:35:30 pm
content: Quote from: Neganur on April 17, 2014, 02:18:04 pmThe user manual is probably designed for the full range from 100MHz to 1GHz scopes and the ones up to 500MHz Bandwidth probably are Gaussian.

author: Neganur
author_rank: Unknown
timestamp: April 17, 2014, 02:43:09 pm
content: Quote from: EV on April 17, 2014, 02:03:53 pmI'm not sure if I measured the 067-0587-02 cal plugin or my Vince pulser #43 with my old Tek 7104 here (with 7B10 and 7A29), bit sloppy photo but I think I can read1.8 div, so 0.35/360 ps ~972 MHz1.4 div, so 0.35/280 ps ~1.25 GHzEDIT: Needed to clean my glasses, hehe.

author: EV
author_rank: Frequent Contributor
timestamp: April 17, 2014, 02:50:54 pm
content: Quote from: Neganur on April 17, 2014, 02:18:04 pmYou have quite big overshoot in this pulse. Have you connected the pulse directly to 50 Ohm input cnnector with BNC cable.I have done so and the rise time i about 350 ps with TEK 284 generator.

author: EV
author_rank: Frequent Contributor
timestamp: April 17, 2014, 03:05:52 pm
content: Quote from: Neganur on April 17, 2014, 02:43:09 pmIt is 067-0587-02 and 1.4* 200 = 280 ps is correct. BW is 350 / 280 = 1.25 GHz. I have also this 067-0587-02.Edit: It gives faster rise time because it is connected directly to the plugin connector without any cables.

author: Neganur
author_rank: Unknown
timestamp: April 17, 2014, 08:49:06 pm
content: Quote from: EVAh yes you're right, for some reason I edited my post and thought "darn, I skipped the 0.4 Div at the bottom", but it's placed to cross the 10% graticule in that intersection on purpose.The connection from the 284 is through 30 cm Air line directly into the scope's 50 Ohm BNC, I didn't have any good coax handy at the moment. I could try again with an external feed-through load but I have no knowledge of its bandwidth, but it should be good enough.

author: EV
author_rank: Frequent Contributor
timestamp: April 17, 2014, 09:35:25 pm
content: The over shoot has been usually under 3 % when tek 284 is connected with BNC cable to 50 ohm input as you can see also in my Reply #79 on: Today at 12:50:54 AM.Quote from: Neganur on April 17, 2014, 08:49:06 pm

author: Neganur
author_rank: Unknown
timestamp: April 18, 2014, 12:30:59 am
content: Took a little longer than anticipated but here is the frequency response of My MSO-X 3104A.Signal generator used is an HP8648B, supposedly not calibrated in magnitude and unknown flatness/ripple (the frequency is verified to be accurate with a good counter)Each magnitude value is a mean value over at least 40 samples, from 1 MHz to 1500 MHz in steps of 1 MHz.Also, another shot with the Tek284, with just a GR874 to BNC adapter. I can't seem to lose the significant overshoot so maybe the unit itself is faulty. I have another Tek284 I could try at some point but it got damaged during transport and I don't have the time to fix it right now.

author: EV
author_rank: Frequent Contributor
timestamp: April 18, 2014, 07:54:14 am
content: You can try your Tek 284 with your Tek 7104 scope using 7B10 and 7A29 plugins. You should get rising pulse which look same as in my picture. If so your Tek 284 is not faulty.Quote from: Neganur on April 18, 2014, 12:30:59 am

author: eurofox
author_rank: Unknown
timestamp: April 18, 2014, 08:28:35 am
content: Quote from: Neganur on April 18, 2014, 12:30:59 amI did the test with my MSO-X 3104A and HP8648C and got the same results.For the rise time testing I'm building now a 35ps pulse generator.eurofox

author: Neganur
author_rank: Unknown
timestamp: April 19, 2014, 02:37:53 am
content: I needed some time to think and also re-read some application notes regarding the results I was getting with the Agilent scope.My Tek 284 might actually not have an issue after all, but my perception of flat roll-off oscilloscopes does.In fact, I'm a bit irritated that I wasn't quite aware of the fact that the 1 GHz 3000X isn't Gaussian. This changes a few things for me:The Oscilloscope Vendor needs to specify system bandwidth for me (specific probe+scope), since the inverse RMS formula* for Gaussian scopes does not apply to Flat systems!*: BW(system) = SQRT((1/BW_probe)^2 + (1/BW_scope)^2)I am able to measure rise time down to about 500 ps more precise than with a Gaussian scope of same bandwidth.Any faster than 500 ps and the Gaussian scope will be more accurate, although both types will have greater than 15% error at that point.I will have rather massive overshoot and ripple when it comes to transient behaviour such as a step response.If my signal rise time is significantly faster than my system rise time (scope+probe), I can estimate the signal rise time by solving for t_r(signal) int_r(measured)=SQRT(t_r(signal)^2+r_t(system)^2)But is this valid for the Flat response scope too?The Flat scope has less sampling alias errors, and also requires a less minimum sampling rate than a Gaussian response scope to reconstruct a signal for the same bandwidthI will be able to measure and capture complex waveforms that consist of frequencies with maximum practical components of 714 MHz or less (i.e. up to 700 ps rise times) accurately, i.e. 3% accuracy.For a 1 GHz Gaussian scope it is 526 MHz (950 ps rise times) at 3% accuracy.This is my first flat response scope, so I'm wondering how much of those gotchas I will run into still. It also makes me wish I had not sold the Tek7104 after all, it would be good to have something to compare against.I'm really worried by the fact that I will see overshoot where a Gaussian scope would not.Mainly because I am not sure I have fully understood what that will mean for me.Like, is this signal really looking like this? How do I know it is my circuit and not the scope behaving differently from what I would expect.What if I am specifically interested in measuring overshoot, I guess I better make sure my signals aren't too fast?Other than that, I think this means that for in-band signals, this scope will serve me extremely well.References:Agilent Application Note 1420

author: EV
author_rank: Frequent Contributor
timestamp: April 19, 2014, 06:57:39 am
content: Yes, picture 2 in this application note explains the over shoot of your scope. Probably I have seen this note but did not remember it any more.Quote from: Neganur on April 19, 2014, 02:37:53 am

author: rf-design
author_rank: Regular Contributor
timestamp: April 19, 2014, 07:46:50 am
content: From the users view the choice is very clear. If you test or adjust your circuit or DUT for overshoot or optimal damping near the bandwidth of the scope a gaussian is optimum. Flat scopes overlap a little bit the capabilities for flat response of other instruments. So I think the trend to flat scopes is driven by the small plus which is given to marketing. The inherent speed of the frontend will not change but you get a better number.For today mid and high-end scopes with digital FIR filters it would be a software option to switch from gauss to flat. But as it seems in scope market there are a very small number of vendors driving the engineering only to incremental, baby steps. That will change if there are new entries in the market for new vendors which are made open by the baby steps.

author: Carrington
author_rank: Super Contributor
timestamp: April 19, 2014, 02:04:49 pm
content: Quote from: Neganur on April 19, 2014, 02:37:53 amQuote from: rf-design on April 19, 2014, 07:46:50 amQuote from: Neganur on April 19, 2014, 02:37:53 amI think exactly the same.More of the same (Selecting-the-right-bandwidth-scope.wmv):http://www.element14.com/community/servlet/JiveServlet/downloadBody/35773-102-1-217101/T%26M-Learning%20Center-Oscilloscopes-Video-Agilent.Training_Videos_10.wmvInevitably, you will need more and more BW.

author: David Hess
author_rank: Super Contributor
timestamp: April 19, 2014, 05:00:12 pm
content: Quote from: rf-design on April 19, 2014, 07:46:50 amI wondered if this would come up in the discussion. I had an opportunity to evaluate a Tektronix MSO5204 (2 GHz and 5 GS/s) a couple of years ago which *sometimes* displayed this problem. When the DSP based bandwidth filters were used, fast transition edges displayed overshoot. When hardware based bandwidth limiting with the same cutoff frequency was used, there was no overshoot.

author: David Hess
author_rank: Super Contributor
timestamp: April 19, 2014, 05:35:07 pm
content: Quote from: Marco on February 02, 2013, 01:50:12 pmAll of the active probes I am familiar with have a 50 ohm output and rely on a 50 ohm termination when used with a high impedance oscilloscope input.There were at one time low input impedance probes intended for use with high impedance inputs which used a transmission line higher than 50 ohms with a similarly high termination resistance included as part of the compensation box but I have not seen one in a long time. Their advantage over standard passive probes was lower input capacitance. With a 100 ohm transmission line and termination, a x10 probe would have a 1k input resistance instead of the 500 ohm input resistance of a 50 ohm probe.

author: David Hess
author_rank: Super Contributor
timestamp: April 19, 2014, 06:52:22 pm
content: Quote from: grumpydoc on February 03, 2013, 05:12:40 pmThe SG503 does not have an external leveling head but does include one before its two x10 switchable attenuator stages.It also specifically states on the front panel that calibration occurs with a specific Tektronix part numbered 50 ohm coaxial patch cable so presumably the cable characteristics are calibrated out.

author: David Hess
author_rank: Super Contributor
timestamp: April 19, 2014, 07:00:55 pm
content: Quote from: Marco on February 02, 2013, 01:49:19 amQuote from: Neganur on April 19, 2014, 02:37:53 amIt is worth noting that lower frequency oscilloscopes, at least Tektronix ones with low frequency extending into the 100s of MHz, were specified for bandwidth *at the probe tip* with specific exceptions. This is from an older (paper!) version of "ABC's of Probes" by Tektronix which is available online as part of Linear Technology application note 47:Most manufacturers of general-purpose oscilloscopes that include standard accessory probes in the package, promise and deliver the advertised scope bandwidthat the probe tip.For example, the Tektronix 2465B 400 MHz Portable Oscilloscope and its standard accessory P6137 Passive Probes deliver 400 MHz (-3db) at the probe tip.However, not all high performance scopes can offer this feature, even when used with their recommended passive probes. For example, the Tektronix 11A32 400 MHz plug-in has a system bandwidth of 300 MHz when used with its recommend P6134 passive probe. This is simply because even the highest impedance passive probes are limited to about 300 to 350 MHz, while still meeting their other specifications.This makes calculating the system bandwidth from the root sum of the squares of the specified probe and oscilloscope bandwidth marginal at best and impossible at worst and cheap oscilloscope manufacturers and marketing droids are hardly going to make it easier.It is worth mentioning that the standard probe tip measurement uses a coaxial probe tip connection, 50 ohm signal source, and 50 ohm termination so the probe tip sees 25 ohms in a coaxial environment which is hardly representative of actual use.QuoteThe only aliasing errors I run across are those caused by nonlinearities in the digitizer itself which mix the incoming signal with the sampling frequency producing products above the Nyquist frequency. Interleaved ADCs are especially prone to this problem as Agilent discusses in one of their application notes. Equivalent time sampling if available largely negates this issue simply by supporting a sampling rate so high that aliasing becomes a non-problem even with a Gaussian response.QuoteI am inclined to think that an old style sampling oscilloscope is an even better choice in this case although they lack a Gaussian response as well. They have the advantage of predictable frequency response and are my go-to tool for calibrating the pulse generators used to calibrate the transient response on analog oscilloscopes.My fastest analog non-sampling oscilloscope is a 500 MHz 7904 and my fastest vertical amplifiers for it are only 400 MHz but wow, it sure works well and especially so with lower bandwidth vertical amplifiers. It is difficult to appreciate how visually clear a high acceleration potential oscilloscope CRT is when used at low bandwidths until you see one. Just that by itself is enough reason to use a 500 MHz CRT oscilloscope in a low bandwidth application and may explain much of the nostalgia for the 2465 series of oscilloscopes.QuoteI started having the same concern after evaluating a couple of low end and high end DSOs which all displayed this problem in one form or another and I suspect oscilloscopes which have "upgradable" bandwidths will suffer from this to an even greater extent. I would much rather have good transient response which I cannot fix than better anti-aliasing since that has been a solved problem, at least for those who understood it, until recently.On one hand, their anti-aliasing prevents aliasing which was not a problem before. On the other hand, the same anti-aliasing messes up the transient response. I am failing to see an advantage here.If I get around to it this weekend, I will post the measured frequency response of my 2232 in DSO mode using an SG503 leveled sine wave oscillator. I have faster DSOs I could test but lack a faster leveled signal source.

author: EV
author_rank: Frequent Contributor
timestamp: April 20, 2014, 07:29:58 am
content: There is overshoot also in the pulse from your Vince's MK2 #43 pulse generator.Quote from: Neganur on April 19, 2014, 02:37:53 am

author: Carrington
author_rank: Super Contributor
timestamp: April 20, 2014, 05:21:30 pm
content: I don't know the JW-32 BW, so suppose that is 1GHz with gaussian response (at least it seems), now the JW-43 have a BW of 1GHz with flat response. So under these conditions, it is clear that for a pulse with a rise time of 200ps both must have an error greater than 20%, in fact, for 500ps already is 20% for both (gaussian and flat). Unfortunately seems that every measure has been taken by a different person, and therefore with different types of generators and cables, so the following comparison is not very accurate, since each system will introduce different artifacts...Anyway, this is the result:JW-43 (red) appears to be less accurate that JW-32 (green), right? However, if I'm not mistaken, for a tr of 700ps JW-43 (flat) should be more accurate than JW-32 (gaussian).Please note that the time axis was modified to match it for all, but the amplitude and delay are incorrect.

author: EV
author_rank: Frequent Contributor
timestamp: April 20, 2014, 06:05:54 pm
content: JW-32 BW is 1 GHz and it is gaussian. Its risetime 20%-80% is 190 ps as it is 200 ps for JW-43. It is a little faster than for JW-43. I attach Vince's test also for JW-32.Quote from: Carrington on April 20, 2014, 05:21:30 pm

author: EV
author_rank: Frequent Contributor
timestamp: April 20, 2014, 06:14:02 pm
content: All JW tests can be seen here:https://www.eevblog.com/forum/blog/eevblog-306-jim-williams-pulse-generator/360/in « Reply #373 on: May 20, 2013, 01:52:27 AM »

author: David Hess
author_rank: Super Contributor
timestamp: April 27, 2014, 09:36:47 pm
content: Here is the plotted frequency response of my Tektronix 2232 in DSO mode using an SG503 leveled sine wave generator up to 260 MHz with 2 nanoseconds of RG-400 cable and a 50 ohm feedthrough termination that is suppose to be good to at least 1 GHz.One curve is with the 2232 alone and the other includes the cheap 100 MHz x10 probe that I normally use with a coaxial probe tip to BNC adapter. The measured bandwidth is 104 MHz for the oscilloscope alone and 106 MHz with the oscilloscope and probe. The probe measurement was done using a different input level and attenuator setting which may have affected the results slightly.Up to about 20 MHz, the oscilloscope absolute level measurement agreed with the output indicator on the signal generator to within 1%.