On Sat, 27 Oct 2018 09:36:54 +0100, Tom Gardner wrote:> On 27/10/18 04:32, Johnny B Good wrote: >> On Fri, 26 Oct 2018 13:27:07 -0700, Klaus Kragelund wrote: >> >>> A 200MHz scope for 379 USD: >>> >>> >> I've been considering replacing my ancient 1950s CRT dual beam 70Lbs >> 'scope with something more up to date recently and this Siglent >> Technologies SDS1202X-E 'scope looked like it might be a good value >> proposition (a snip at a mere £363.05 for UK customers via Amazon's >> 'Fulfilment' delivery) so have checked out some reviews[1] which seem >> to confirm this view. >> >> However, this is a subject of very recent interest so I haven't yet >> researched this in any great depth as yet so I was wondering if you had >> any advice on this 'scope or possibly better alternatives (100MHz B/W >> dual trace at a minimum) that you could offer to aid me in my search >> for a reasonably specced and priced unit? > > This topic comes up once per week on EEVBlog forum, and is discussed ad > nauseam there. Many of the responses are "just buy X it is the best > available now", but a few are more measured.I've looked at few of those reviews now and I'm more than mindful of their very short BB dates for such rapidly evolving kit. Apropos of which, the Rigol DS1052E, a ten year old design which I referred to in note [2] at the end of this post, which is still being sold by Rigol uk at just a hundred quid less than the asking price for an SDS1202X-E.> > There are also some long /long/ threads on reviews of the popular > bottom-end scopes.I haven't explored any of those threads (assuming you're referring to the comments below the youtube vids) in any depth so far.> > Read EEVBlog forum and you will have a better idea of what questions you > should ask, and some answers for them.Thanks for the suggestion. I'll google my way to that forum now that I've read the wikipedia article on oscilloscopes by way of a refresher/ technology update course. Mind you, I have to say that the Siglent Technologies SDS1202X-E is still looking like the "Best Bang for my Buck" option right now despite it still being quite a chunk of cash to part with in one go. There are plenty of alternatives at modestly cheaper price points but they seem to leave you rather short changed by charging extra for optional (and useful) features that come as standard with the SDS1202-E.> > Don't throw the boat anchor away until you are satisfied that the new > scope can do everything you want at least as well as the boat anchor.Well, I've just ventured into our basement (one time radio shack and workshop that became a rather neglected facility when I went self employed some 23 years ago) to take a look at this venerable "boat anchor" to try and note make and model details and confirm its dual beamness (my recollection of this feature is a little bit hazy to say the least after some 20 years of neglect). At first, I couldn't locate it from amongst the original inventory plus the additional junk accumulated over the past two decades or so but more careful scrutiny revealed its presence on the dexion shelving tucked right into the back corner of the basement, a location where access is currently blocked by a pile of junk heaped on the floor. It wasn't quite as imposing a boat anchor as I'd been expecting and that with its matt black paint job had helped camouflage it from my initial scan of the dexion shelving. Anyhow, I wasn't about to initiate another clear-out and I didn't want to expend energy on merely moving the clutter to another part of the basement so its spec remains a mystery for the time being. That corner of the basement was the driest part so it's quite possible (exploding electrolytics hazard aside) that it might still be in a serviceable condition, assuming the HT windings on its BFO mains transformer haven't succumbed to the very real possibility of 'green spot' failure (AFAICR, the transformer(s) had all been impregnated with bitumen sealing compound as was the practice of the day back in the 40s and 50s so might still be 'green spot' free even now). AFAICR, its bandwidth was a mere 5MHz at best (certainly nowhere near 10MHz or above) so really only good for audio frequency work which is what I'd really purchased it for way back in the early 70s (most likely from my local WD surplus shop). I'd been building a 200W RMS per 4 ohm load stereo PA amp of my own unique design using ex main frame computer PSU parts (also from my local WD surplus shop) and a cheap 'scope seemed like a useful item of test kit to help me test my amplifier designing efforts. The need to record wave traces led me via the art of oscillography into a more general interest in photography since the 'weapon of choice' for this work was the SLR camera. If nothing else, I have good enough reason to hang onto this venerable bit of kit, even if only as a 'keepsake' rather than bust a gut trying to get rid of it. :-) Other than the initial oscillography, it never saw a lot of use. However, its 1v 50Hz mains derived calibration test voltage did eventually reveal that the slightly flat topped mains voltage waveform, that I'd assumed was possibly an artefact of the BFO mains transformer's loading or possibly an iron core saturation effect, turned out to be the real waveform of the mains supply. When I powered it up via my 2nd hand APC SmartUPS2000 2KVA/1500W line interactive Pure Sine wave UPS and unplugged it from the mains supply to switch over to battery power the visibly distorted sine wave magically morphed into a perfect sine wave (with just a slight hint of the 5KSa/s ripple from the class D inverter used to synthesise the sine wave output). A little while later, when I was repeating this test of UPS and petrol (gasoline) powered generator sine wave purity using Cool Edit Pro on a laptop to record a sample of the mains voltage obtained using an old 6vac wallwart transformer with resistor network attenuator into the line in on the laptop's sound adapter's interface, I saw exactly the same waveforms which neatly removed any question of 'transformer distortion' from the equation. It turns out the purity of the UK's national grid 50Hz sine wave supply is somewhat lacking even when compared to that of a cheap 2.8KVA generator [1]. For reference, it's more accurately best described as having a 'down sloping' flat topped appearance (with respect to absolute amplitude - it's an 'up-slope' on the negative peaks). I make this reference for the benefit of those armed only with a cheap digital 'scope[2] that simply shows a flat topping effect without any hint of a slope on the mains waveform versus the more pure looking sine wave from a cheap 1KW Parkside inverter generator (PGI 1200 B2). [1] Curiously, the quality of the UPS's sine wave inverter output was comparable to that of the single phase single pole pair generator head used on the cheap 2.8KVA generator in that both exhibited a high frequency (circa 5KHz) ripple superimposed on the 50Hz fundamental. In the case of the generator this is an artefact known as 'slot winding ripple'. In both cases, such high frequency ripple is of absolutely no consequence to even the most fussiest of mains voltage power supplies used by the most sensitive items of "Electronic Equipment". What makes such cheap generators unsuitable for use with "Sensitive Electronic Equipment"(tm) is their over-volting response to modest amounts of capacitive loading, a characteristic that's totally absent from inverter gensets, hence their suitability so often and (for once) justifiably advertised, for use with such "sensitive equipment". [2] For example the Rigol DS1052E being used here by Chris Howard (callsign GOMTCH) in his youtube video of a test he did with a Parkside PGI 1200 B2 inverter genset <https://youtu.be/JTTGvjbY8_s?t=403> After identifying the scope being used in this youtube video, I was able to google for reviews which revealed that it's a ten year old model that's now long since passed its BBD. I did note a reference to an 8 bit (256 levels) vertical resolution and the use of a 320 by 240 pixel screen which just might account for it failing to accurately show the sloped flat topping of the mains supply voltage in this video. However, the fact that both this and the SDS1202X-E both have vertical ADC resolutions limited to just 8 bits suggests the latter might also fail to miss such subtleties as the sloped flat topping of the UK mains voltage waveform that is so clearly and unambiguously displayed on a classic CRO. The doubled vertical resolution of the SDS1202X-E's 800 by 480 pixel display might mitigate this shortcoming to some extent. This curious stagnation of vertical resolution over the past decade probably explains why there is still a fondness for the classic CRO and a lingering sense of dissatisfaction with the new fangled DSO (at least at the entry level end of that market segment). Perhaps I should be looking out for the use of 10 and 12 bit vertical resolutions in the specifications of any candidate DSOs that take my fancy. No doubt there'll most likely be an added cost for such improved resolution. :-( -- Johnny B Good
amazing ARB pricing
Started by ●October 25, 2018
Reply by ●October 27, 20182018-10-27
Reply by ●October 27, 20182018-10-27
On Sat, 27 Oct 2018 14:50:08 -0700, Joerg <news@analogconsultants.com> wrote:>On 2018-10-25 14:27, John Larkin wrote: >> >> >> https://www.amazon.com/Adoner-Precision-Arbitrary-819214bits-Modulation/dp/B07BF7Y7TJ/ref=sr_1_3?ie=UTF8&qid=1540502597&sr=8-3&keywords=fy6600&dpID=41vbYI%252B7YiL&preST=_SX342_QL70_&dpSrc=srch >> >> Other places have this box for $99. >> >> > >I have a no-name ARB because I needed one year ago for aerospace >testing. The 1st one had a bum FPGA. Was replaced. The 2nd one now has a >slowly failing rotary encoder. Oh well.Even if they are junk, I can't understand how or why they would sell all that for $99. -- John Larkin Highland Technology, Inc lunatic fringe electronics
Reply by ●October 27, 20182018-10-27
On Saturday, 27 October 2018 04:32:42 UTC+1, Johnny B Good wrote:> On Fri, 26 Oct 2018 13:27:07 -0700, Klaus Kragelund wrote: > > > A 200MHz scope for 379 USD: > > > > I've been considering replacing my ancient 1950s CRT dual beam 70Lbs > 'scope with something more up to date recently and this Siglent > Technologies SDS1202X-E 'scope looked like it might be a good value > proposition (a snip at a mere £363.05 for UK customers via Amazon's > 'Fulfilment' delivery) so have checked out some reviews[1] which seem to > confirm this view. > > However, this is a subject of very recent interest so I haven't yet > researched this in any great depth as yet so I was wondering if you had > any advice on this 'scope or possibly better alternatives (100MHz B/W > dual trace at a minimum) that you could offer to aid me in my search for > a reasonably specced and priced unit? > > [1] Amazon customer reviews here: > > <https://www.amazon.co.uk/Siglent-Technologies-SDS1202X- > Oscilloscope-Channels/dp/B06XZML6RD/ref=sr_1_1? > ie=UTF8&qid=1540608976&sr=8-1&keywords=sds1202x-e> > > TinyURL <https://tinyurl.com/ydgpong6> > > (click the customer reviews link near the top of the page) > > > The Defpom's Repair Channel review videos here: > > <https://youtu.be/64kxGDOg7es?t=19> Part 1 > <https://youtu.be/laK1v2Zas4o?t=12> Part 2If you're only doing audio the boat anchor should be plenty. It's 5x faster than my first scope. Or you could upgrade to the £11 DSO-138 with all of 200kHz bw :) Seriously, although that's beyond basic, it's also tiny enough and cheap enough to take to any job anywhere anytime. I do that with multimeters, as well as decent ones I got a clutch of £2.34 ones that I can leave in potentially convenient places and take anywhere without concern. They've been handy in all sorts of situations where I would not have thought to take a proper meter. For 100MHz there's a fair assortment of used scopes on ebay, some at good prices. And some definite horrors. NT
Reply by ●October 28, 20182018-10-28
John Larkin wrote:> On Sat, 27 Oct 2018 14:50:08 -0700, Joerg <news@analogconsultants.com> > wrote: > >> On 2018-10-25 14:27, John Larkin wrote: >>> >>> >>> https://www.amazon.com/Adoner-Precision-Arbitrary-819214bits-Modulation/dp/B07BF7Y7TJ/ref=sr_1_3?ie=UTF8&qid=1540502597&sr=8-3&keywords=fy6600&dpID=41vbYI%252B7YiL&preST=_SX342_QL70_&dpSrc=srch >>> >>> Other places have this box for $99. >>> >>> >> >> I have a no-name ARB because I needed one year ago for aerospace >> testing. The 1st one had a bum FPGA. Was replaced. The 2nd one now >> has a slowly failing rotary encoder. Oh well. > > Even if they are junk, I can't understand how or why they would sell > all that for $99.They seem not to understand that they can make much better quality for a little more money. It might be symptomatic of copying the design in the first place.
Reply by ●October 28, 20182018-10-28
Carl wrote:> Tom Del Rosso wrote: >> Just how arbitrary is an ARB? Can any of them download a waveform >> from a scope and make little adjustments like reducing overshoot or >> ringing, so you can see if doing so would help before you go to the >> effort of reducing it for real? >> >> Or do they just do complex modulations, or is it just another name >> for function generator? > > Some may be able to download directly from a scope but it would > probably have to be the same brand. They usually have front panel > waveform creation and editing where you can step through a waveform > point by point and either directly enter a numerical value or use the > up and down arrows to modify it. All should be able to talk to a PC, > and the scope should also be able to talk to the PC so you should be > able to upload a waveform with the scope software, either save it > directly or export as a CSV file depending on the brands, then import > into the ARB software, edit as desired, and then download. The > waveform is point-by-point completely arbitrary but then you have to > take into account the sample rate and bandwidth of the ARB to > determine just how sharp a corner you can actually get and also what > the actual output frequencies will be (if the scope and ARB sampling > rates differ, for example). They are great fun to play with, and > actually useful too :-). One gotcha for me with the cheap ARBs in > this thread is that the longest a single waveform can be is only 8192 > points. I assume that you can slow down the sample rate to extend > that in time but eventually you hit the minimum required bandwidth. > They can store 64 waveforms and might be able to chain waveforms > together with no glitches or timing issues which would allow one 512 > Kpt waveform but you would have to handle the breaking apart and > downloading in software. I haven't read the manual to see if all > that would work.Thanks, I suspected as much. There's still lots of room for improvement in the software to cut the number of steps. I assume the memories are so small because they used a small FPGA with not enough address lines. That's another place where they could improve it a lot for a few dollars.
Reply by ●October 28, 20182018-10-28
On 27/10/18 23:07, Johnny B Good wrote:> It turns out the purity of the UK's national grid 50Hz sine wave supply > is somewhat lacking even when compared to that of a cheap 2.8KVA generator > [1]. For reference, it's more accurately best described as having a 'down > sloping' flat topped appearance (with respect to absolute amplitude - > it's an 'up-slope' on the negative peaks). I make this reference for the > benefit of those armed only with a cheap digital 'scope[2] that simply > shows a flat topping effect without any hint of a slope on the mains > waveform versus the more pure looking sine wave from a cheap 1KW Parkside > inverter generator (PGI 1200 B2).The "clipped sine wave" appearance surprised me, when I looked at it for the first time since the 70s. I believe it is because there has been a change in the loads on the grid. Nowadays there are a large number of devices with SMPSs. Many presume a more-or-less constant input voltage throughout the mains cycle, so they rectify the and smooth the mains, "topping up" the charge in the capacitor only at the peak voltages. Hence significantly more current is drawn at the peaks than at other parts of the cycle. As for inverters (i.e. not petrol-driven generators), I would be wary about applying a "modified sine wave" output to valuable equipment. The PSU might be unfazed by such rectangular input, but in cheap equipment, who knows.
Reply by ●October 28, 20182018-10-28
On 27/10/2018 23:36, John Larkin wrote:> On Sat, 27 Oct 2018 14:50:08 -0700, Joerg <news@analogconsultants.com> > wrote: > >> On 2018-10-25 14:27, John Larkin wrote: >>> >>> >>> https://www.amazon.com/Adoner-Precision-Arbitrary-819214bits-Modulation/dp/B07BF7Y7TJ/ref=sr_1_3?ie=UTF8&qid=1540502597&sr=8-3&keywords=fy6600&dpID=41vbYI%252B7YiL&preST=_SX342_QL70_&dpSrc=srch >>> >>> Other places have this box for $99. >> >> I have a no-name ARB because I needed one year ago for aerospace >> testing. The 1st one had a bum FPGA. Was replaced. The 2nd one now has a >> slowly failing rotary encoder. Oh well. > > Even if they are junk, I can't understand how or why they would sell > all that for $99.Presumably because they can make them in bulk for less than $80 and are content with a rather small margin on each sale. I am tempted to get one but so far I have resisted. Sooner or later I will find an excuse to buy one and clutter up my equipment rack some more. I presume the model of choice is the 14bit DAC version but which of the many "brands" of identical spec kit is the original design or are they all made in one factory and badged by the resellers (much like some LCD TVs). -- Regards, Martin Brown
Reply by ●October 28, 20182018-10-28
On 27/10/18 03:23, George Herold wrote:> On Friday, October 26, 2018 at 4:27:11 PM UTC-4, Klaus Kragelund wrote: >> A 200MHz scope for 379 USD: >> >> https://www.amazon.com/Siglent-Technologies-SDS1202X-Oscilloscope-Channels/dp/B06XZML6RD/ref=pd_aw_sbs_328_of_13?_encoding=UTF8&pd_rd_i=B06XZML6RD&pd_rd_r=0578ee0f-d95c-11e8-8a27-e7c97784a407&pd_rd_w=dV3r6&pd_rd_wg=B2YIF&pf_rd_i=mobile-dp-sims&pf_rd_m=ATVPDKIKX0DER&pf_rd_p=926ebe02-3236-40c6-ac63-01ad178f498a&pf_rd_r=Y2SMMGCRT1ZGCYBYF1GE&pf_rd_s=mobile-dp-sims&pf_rd_t=40701&psc=1&refRID=7M8XSZS3XF3JSQZ68R27 >> >> Cheers >> >> Klaus > > I'm totally in love with this keysight 'scope, but I think it's > close to ~$1k.. it just does everything right. > (and it all starts with the triggering.) > > I turn it on and it remembers all the last settings, > all stuff should do that. > > George H. >All stuff *used to* do that. Welcome to the new age. Jeroen Belleman
Reply by ●October 28, 20182018-10-28
Tom Gardner <spamjunk@blueyonder.co.uk> wrote:> I believe it is because there has been a change in the loads > on the grid. Nowadays there are a large number of devices > with SMPSs. Many presume a more-or-less constant input voltage > throughout the mains cycle, so they rectify the and smooth the > mains, "topping up" the charge in the capacitor only at the > peak voltages. Hence significantly more current is drawn at > the peaks than at other parts of the cycle.More modern SMPSs should fix that by having PFC (Power Factor Correction). It basically is an extra switching boost-converter in front of the main capacitor operating from unsmoothed rectified mains, it converts the half-sinewave voltage to a constant voltage to charge the capacitor. (the working point of the converter is changing all the time in the rhythm of the mains voltage) Of course there still exists a lot of equipment without this, now manadatory, feature. And it is not required for lowpower devices, which become more and more prevalent.
Reply by ●October 28, 20182018-10-28
On 28/10/18 13:24, Rob wrote:> Tom Gardner <spamjunk@blueyonder.co.uk> wrote: >> I believe it is because there has been a change in the loads >> on the grid. Nowadays there are a large number of devices >> with SMPSs. Many presume a more-or-less constant input voltage >> throughout the mains cycle, so they rectify the and smooth the >> mains, "topping up" the charge in the capacitor only at the >> peak voltages. Hence significantly more current is drawn at >> the peaks than at other parts of the cycle. > > More modern SMPSs should fix that by having PFC (Power Factor Correction). > > It basically is an extra switching boost-converter in front of the main > capacitor operating from unsmoothed rectified mains, it converts the > half-sinewave voltage to a constant voltage to charge the capacitor. > (the working point of the converter is changing all the time in the > rhythm of the mains voltage) > > Of course there still exists a lot of equipment without this, now > manadatory, feature. And it is not required for lowpower devices, > which become more and more prevalent.What's not clear to me is whether the large number of "low power" PSUs in domestic equipment is sufficient to clip the peaks. I'm open to other suggestions, of course.
