70 MHZ Oscilloscope with higher rated probes - Page 1
Forum section: electronics / beginners

author: Rick King
author_rank: Contributor
timestamp: April 15, 2021, 03:09:14 pm
content: Hi,My first post and a retired beginner for hobby.First, I searched the web and here for a previous post so not to duplicate (i.e. eevblog.com: probes on Google.) So, sorry if I did.So you know my use: Only Hifi amplifiers, Tape decks etc. Keep in mind I am a newbie and learning, although I retired from IT. I may be way off base in my thinking. Reading a lot of books and watching EEVBlog videos. I may be ahead of myself in my learning curve. At my age I am trying to learn only what I need to know for hobby and probably missing a lot of basics.I bought a cheap scope (Hantek 70 MHz, although has decent reviews) to learn with. I also purchased extra 200 MHz probes. I'm not sure if I needed them. When looking at SINE waves from a Audio Function Generator the signal seems distorted at x10 and even worse with the 200 MHz probes. [Probably not the best way to get a signal, but using software as opposed to a proper stand-alone Signal Generator, which may be the problem] Lastly, I have calibrated and also tried to fine-tune with the screws on the probe; which helped a little.I guess my question is guidance. Do I need 200 MHz probes? Should I buy a separate unit? Many of the HiFi techs I talk to say they don't use one that often. Any recommendations for a better learning path would be welcomed as well. Hope I have made some sense.Cheers!RickP.S. I am not thin skinned. I can handle directness. Just want to learn.

author: tggzzz
author_rank: Super Contributor
timestamp: April 15, 2021, 03:25:40 pm
content: Welcome. Thinkg and wanting to learn are a good starting point.I can't think what you might mean by "distortion"; a photo would help, as might a description of your probing technique.200MHz probes will be fine,but their extra bandwidth will be "wasted".You may find it helpful to read the references athttps://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/particularly the "ABC" guides and the safety guides.

author: radiolistener
author_rank: Super Contributor
timestamp: April 15, 2021, 03:56:36 pm
content: wide bandwidth probes are bad for digital oscilloscope with low bandwidth. It's better to use the probe with narrower bandwidth than your oscilloscope input bandwidth. This is because it's better to cut-off high frequency components, because otherwise it will be folded into higher Nyquist zone of ADC and leads to a signal distortion due to aliasing.For a clean signal which bandwidth completely fits into the first Nyquist zone (half of the sampling rate) you will not notice any problem. But when signal consists of high frequency components you will see significant difference.Do you measure D-class amplifier? What kind of distortion you're talking about?

author: tggzzz
author_rank: Super Contributor
timestamp: April 15, 2021, 04:19:17 pm
content: A probe's frequency rolloff is much too poor and poorly defined to be of any use as an anti-aliasing filter.The scope should incorporate the specific anti-aliasing filter that the scope needs. If not, then get another scope. (There are rare counter cases, but they are not relevant to a beginner)

author: bdunham7
author_rank: Super Contributor
timestamp: April 15, 2021, 04:30:15 pm
content: Describe your Audio Generator and post a screenshot of the distorted waveform. Also, the exact model of the scope?Are you saying the the signal isnotdistorted using the 1X setting on the Hantek probes? Have you calibrated the probes using the scopes calibrator output? What frequency sine wave are you trying?

author: Vovk_Z
author_rank: Super Contributor
timestamp: April 15, 2021, 04:43:47 pm
content: Probe bandwidth doesn't matter. It may be 50 MHz or 500 MHz. It only must be calibrated with the exact input. That's all. Wider bandwidth is almost always better then narrow.

author: Rick King
author_rank: Contributor
timestamp: April 15, 2021, 05:07:21 pm
content: Really appreciate the responses. It must be very frustrating trying to help someone (like me) that has no clue what they are doing, or how to ask a proper or relevant question.I will respond back fully in an hour with some images.I will say that I am just experimenting right now (learning). I don't know enough to start testing my stereo components. Connecting directly from an iPad with EE Toolkit Audio Function Generator. I made new cables to connect directly to the probes rather than several adapters and the signal is cleaner.Thank you!!Back in a few...Rick

author: radiolistener
author_rank: Super Contributor
timestamp: April 15, 2021, 05:39:47 pm
content: Quote from: tggzzz on April 15, 2021, 04:19:17 pmyes, probe frequency rolloff is not the best, but it helps to reduce high frequency components to eliminate aliasing issue. Especially for a slow time/div modes which is required to analyze low frequency audio signals. And it's better than no filtering at all when you use very wide bandwidth probe with low bandwidth oscilloscope.Quote from: tggzzz on April 15, 2021, 04:19:17 pmYes, good oscilloscope should have antialias filter on the input. But using narrow bandwidth probe helps to reject unwanted high frequency components much better.For example oscilloscope antialiasing filter may reject some component for 30 dB. And narrow bandwidth probe provide additional 30 dB rejection. In total we have 30+30 = 60 dB rejection. When you use wide bandwidth probe you will get just 30 dB rejection, which is not enough to not see unwanted aliasing.Cheap oscilloscopes, like these 70 MHz may not have antialiasing filter at all.For example FNIRSI-1013D shows aliasing distortions because it's specification bandwidth is higher than the half of it's ADC sample rate.But the thing going to be much worseif you needsto measure low frequency signals(this is exactly the case of topic starter) and your oscilloscope has too small memory or too slow DSP (which is guaranteed for a cheap oscilloscopes). In such case oscilloscope needs to force reduce ADC sample rate for slow horizontal resolutions. Because it will be unable to capture and process enough sample count at full ADC speed for a long time interval (which is required to see a low frequency waveforms).In such case internal antialiasing filter of oscilloscope cannot help, because it's cut-off is much higher than half sample rate for selected mode and your waveform will suffers distortions due to aliasing. This is a standard issue for a slow time/div modes in a cheap oscilloscopes.Quote from: Vovk_Z on April 15, 2021, 04:43:47 pmthis is false information. Using expensive wide bandwidth probe with a cheap narrow bandwidth oscilloscope may leads to a waveform distortion due to aliasing. How much worse depends on the used antialiasing filter and osclilloscope bandwidth to oscilloscope sample rate relation and also oscilloscope memory size and it's DSP/CPU speed. For a cheap oscilloscope it may be very bad and very noticeable.

author: Rick King
author_rank: Contributor
timestamp: April 15, 2021, 06:26:54 pm
content: I will try to explain what I am thinking in my head so you can help me better. I appologize that I was not clear.My whole mindset, right or wrong, is setup. Am I using the right probes and setup for learning. I am also reading and watching videos from basic elctronics level. I understand in principle the concept of circuitry and know what all the components are. I am still learning how they work together to form a functional unit (i.e. amplifier). At times I want to get away from the "books" and learn the equipment; and the oscilliscope is what I started playing with lately. Before I spent weeks on a multimeter. I will get back to the multimeter later. I want to know the basics of each of my tools for now instead of staring at them.I picked up a Hantek DSO5072P 70 MHZ Scope for learning. I have no idea what I untimately need. One of the reviews said to upgrade the probes. I purchased 200 MHZ probes based on the fact that they were more expensive. Don't laugh.I set the Scope and calibrated probes per the manual. I then wanted to learn about Signal Generarators. Rather than purchase one, I purchased an iPad app (actually paid for it) to learn what it does.What I found was that with a SINE wave it was fairly clear using either probe. When I switch to SQUARE wave its where most of distortion is. I think my connections were bad when I first posted.The real question initially was: Does it matter which probes I use; 80 MHZ or the 200MHz. I was thinking I needed the best setup I could get for learning so that I could see what it does. I was concerned that if my basis for learning was off, it would effect knowing what a good signal should look like; for my scope. I have seen what a Siglent looks like.I could go on, but let me post some images to see my current state.

author: Vovk_Z
author_rank: Super Contributor
timestamp: April 15, 2021, 06:41:11 pm
content: About last picture with a squre wave: it is 1 kHz signal, so 70 or 200 MHz BW probes doesn't matter. I guess this signal is so bad at its sourse.And don't forget to use always 10:1 divider (otherwise any probes will affect a circuit by their capacitance).

author: radiolistener
author_rank: Super Contributor
timestamp: April 15, 2021, 06:46:34 pm
content: Quote from: Rick King on April 15, 2021, 06:26:54 pmThat's the problem of your signal source. iPhone has something like 48-96 kHz sample rate (like any other sound card) and a low pass antialiasing filter on the output, so it cannot produce nice square wave. You're needs a good signal generator in order to get more nice waveforms

author: Rick King
author_rank: Contributor
timestamp: April 15, 2021, 06:50:19 pm
content: Quote from: radiolistener on April 15, 2021, 06:46:34 pmOK. That makes since. In the future, when I do start using these tools for "HiFI components"; will the SQUARE wave be used?

author: radiolistener
author_rank: Super Contributor
timestamp: April 15, 2021, 06:55:53 pm
content: Quote from: Rick King on April 15, 2021, 06:50:19 pmSmartphone as a signal source for HiFi component testing is a very bad choice. I recommend you to buy a good old (used) analog signal generator. If you're interested in just an audio circuits, not HiFi or audiophile, you can buy some cheap Chinese signal generator like FY6800. They have about 45 dB dynamic range. This is not HiFi, but good enough for a regular audio component testing.Another way for audio component testing is to buy some professional audio card like EMU with a good dynamic range and use special software for PC. It produce specific signal output and then analyze how it was changed on the input and displaying you frequency response and many other measurement details, like IMD distortions level, etc.

author: Rick King
author_rank: Contributor
timestamp: April 15, 2021, 06:59:05 pm
content: I really, really appreciate you guys taking the time to answer my questions; and yes it is helpful. I feel like a mouse walking around with giants, but gentle giants.Further comments are welcomed.Thank you sincerely,Rick

author: bdunham7
author_rank: Super Contributor
timestamp: April 15, 2021, 07:15:12 pm
content: Quote from: Rick King on April 15, 2021, 06:50:19 pmYou've discovered Gibbs and Nyquist all at once! Presumably the output DAC for the iPad is 48kSa/s (48,000 samples per second)https://en.wikipedia.org/wiki/Gibbs_phenomenonhttps://en.wikipedia.org/wiki/Nyquist%E2%80%93Shannon_sampling_theoremYour scope is working OK from the looks of it. The bandwidth of the probe is much less important than it's other qualities and how well it is calibrated, especially at audio frequencies. As far as square waves, yes they can be used to test audio equipment if you have sufficient understanding, but first you have to understand what a square wave actually represents. Then you have to understand group delay and phase response so that you can understand what to expect from various audio circuits. I'd suggest you keep it simple for now, especially if you want to use a software signal generator.

author: tggzzz
author_rank: Super Contributor
timestamp: April 15, 2021, 07:16:15 pm
content: Quote from: radiolistener on April 15, 2021, 05:39:47 pmIf you choose a particularly crap scope to justify your statements, then you are making a mistake.If you are considering noise at low sweep speeds, then you should consider using an external low pass filter to limit the noise. It will also be useful to consider the scopes quantisation noise at the relevant signal levelsOut of curiosity,how much experience do you have with designing DSP systems?

author: bdunham7
author_rank: Super Contributor
timestamp: April 15, 2021, 07:35:29 pm
content: Quote from: radiolistener on April 15, 2021, 05:39:47 pmMaybe in some extreme case, but this scope--like most--has a 20MHz bandwidth filter that ought to be engaged when measuring slow signals HF signal noise is any concern. Aliasing a 1GSa/s scope, no matter how crappy, at audio frequencies, seems unlikely. As for lower sampling rates due to memory limitations, the square wave he demonstrates works out to a sampling rate of 12.5MSa/s (40K record length, 3200uS on screen) for a 6.25MHz Nyquist. The BW filter won't help if there were HF noise, but the probe bandwidth won't matter either.

author: Vovk_Z
author_rank: Super Contributor
timestamp: April 15, 2021, 07:38:03 pm
content: Quote from: radiolistener on April 15, 2021, 05:39:47 pmOf cause, you are right too, but I can't agree with you totally, because of several reasons.Yes, aliasing is a weak side of any digital scope, but to fight with it by an unknown amplitude-frequency characteristic of a probe is not reliable.What you say, as for me, means that for the same signal a digital scope has to have wider bandwith (up to several times) then analog one. This is a drawback - working with a digital scope you always have to take into consideration a possible aliasing.A frequency response of a cheap non-brand probe is usually 'wavy' and unknown. So (as for me again) I would rather have a good high-BW probe than cheap, which works like filter but very unknown filter.

author: Vovk_Z
author_rank: Super Contributor
timestamp: April 15, 2021, 07:41:06 pm
content: I mean I would better have one onknown variable (aliasing) than two unknown variables - aliasing and low-BW probe.

author: Rick King
author_rank: Contributor
timestamp: April 15, 2021, 08:41:41 pm
content: Until I buy a "real" signal generator, would I be better off using my PC and the external DAC? It will output up to 32-bit 384khz.

author: Kleinstein
author_rank: Super Contributor
timestamp: April 15, 2021, 09:18:45 pm
content: The PC sound-cards often contain a reconstruction filter. So even if the DAC may be 192 kHz the actual BW may still be limited (in the extremes some 22 kHz).The sampling rate is not enough to make sure to get higher bandwidth output.For just audio a normal soundcard is fast enough though.To get some higher frequency contend, one may consider building a simple square wave souce (e.g. NE555 based). The harmonics extened to beyound 100 kHz and the shape of the transitions can tell a little about the higher frequency range - though a bit tricky to interprete for a beginner.Ususally a faster probe is OK, especially in the low cost range. Even the cheap probes usually come as 100-150 MHz.

author: Rick King
author_rank: Contributor
timestamp: April 15, 2021, 09:29:40 pm
content: Between the two, the PC DAC looks good in all waveforms up to about 22.0500KHz if I configured it right.

author: radiolistener
author_rank: Super Contributor
timestamp: April 15, 2021, 09:32:16 pm
content: Quote from: tggzzz on April 15, 2021, 07:16:15 pmAs I know, almost all budget oscilloscopes with price up to 500 USD have aliasing issue at slow sweep. They are not crap and have antialiasing filter. But they have just 14-28 megapoints memory which is just 14-28 ms. This is not too much for a low frequency audio signals, because 14 ms is a one period for 71 Hz. Many other oscilloscope have even smaller memory.Quote from: tggzzz on April 15, 2021, 07:16:15 pmCannot say exactly, as I remember I made my first DTMF recognition firmware on a PIC16F84 microntroller at about 1995 as a student. Probably this was my first project which utilized signal processing. If we're talking about deep signal processing and ADC/FPGA stuff - about 8 years. Actually I'm software engineer, electronics is my hobby, but before I go into software stuff I also completed education for digital electronics and computer design.Just a month ago I made my own 14-bit oscilloscope with ADC running at 96 MHz (high speed ADC + FPGA + GMII ethernet + software processing on PC), here is screenshot of 1 MHz a square wave output from PSG9080 with no antialiasing filter and with 30 MHz LPF.

author: David Hess
author_rank: Super Contributor
timestamp: April 16, 2021, 03:37:32 am
content: There is nothing wrong with higher bandwidth probes on a lower bandwidth oscilloscope.Instead of thinking of the oscilloscope probe's bandwidth specification as its -3dB point, consider it to be the highest usable frequency before aberrations in the probe's response corrupt the signal. This becomes apparent with a high frequency transient response test on a probe which has a lower bandwidth than the oscilloscope; the oscilloscope will display aberrations caused by the lower bandwidth probe.

author: bdunham7
author_rank: Super Contributor
timestamp: April 16, 2021, 04:20:59 am
content: Quote from: Rick King on April 15, 2021, 08:41:41 pmYes, give it a try and see how it looks. Keep in mind that the distortion you saw on your square wave was not a result of the Nyquist limit, but rather of the output filter required to avoid it. With a higher sampling rate, the transition frequency might not be any higher, but they can use a simple first or second order filter.

author: jdutky
author_rank: Regular Contributor
timestamp: April 17, 2021, 08:00:13 am
content: Quote from: Rick King on April 15, 2021, 06:26:54 pmWhat you are seeing on the square wave is called "ringing" and it is caused by the way you have tried to probe the signal, not by the signal source or the bandwidth of the probes you are using. I'm guessing that you used the 3 inch or 6 inch ground leads that came with your probe to connect to the signal ground. That lead is adding a lot of inductance to your measurement and causing the ringing you are seeing on after the rise and fall of the square wave. If you really want to reduce the ringing you need to reduce the length of your ground loop, either by using a ground spring (which probably came with your probe) or by using a probe-tip to BNC adapter (if you are getting your signal from a BNC connector).Here is a good video that spends some time talking about probe grounding techniques:As to the question about using high bandwidth probes on a low bandwidth scope: it's better to use the probes that came with your scope, but if the "high bandwidth" probes are of the cheap Chinese variety, it may not be making all that much difference. Still, it would be better to get probes that are properly matched to the scope, both in bandwidth rating, and in capacitance.Probes have a compensation network that allows you to match the probe to the instrument. Most of the compensation adjustment is done by an adjustable capacitor, and the probe documentation should tell you what the range of that adjustment is. What you need is a probe whose compensation range contains the input capacitance of your scope. Your scope's documentation should tell you what the input capacitance is. As an example, I have an old Tektronix 475, a 200 Mhz analog oscilloscope, with an input capacitance of 20 pF. I bought cheap Chinese probes on Amazon rated at 200 MHz with an input capacitance adjustable from 13 pF to 25 pF, so those probes can be compensated to match my scope.Higher bandwidth probes often have lower compensation ranges than lower bandwidth probes, and higher bandwidth scopes have lower input capacitance than lower bandwidth scopes. If the compensation range for you probe does not encompass the input capacitance of your scope you will not be able to properly compensate the probe, and you will get distortion of your measurements. So, best to get probes that are well matched to your scope, both in bandwidth, and in compensation range.As for using your probes to filter out high bandwidth components of your measured signals, that is probably not an issue. While I am quite happy with the 200 MHz cheap Chinese probes I bought (you can't go far wrong for $15), other people have reported that the Chinese probes are actually much lower bandwidth than their specs indicate. So, even though you bought 200 MHz probes, you may actually have only 100 MHz probes. In order to test that you would need a much better signal generator than you probably have on hand, and since your scope is only 70 MHz, it's not even worth worrying about. Suffice to say that your 200 MHz probes are probably not causing your noticeable problems, assuming that you were able to properly compensate them (which you said you did).-- Jeff Dutky

author: David Hess
author_rank: Super Contributor
timestamp: April 17, 2021, 03:43:13 pm
content: Quote from: jdutky on April 17, 2021, 08:00:13 amThat is usually the case but not always. In the example I gave of a low bandwidth probe used with a high bandwidth oscilloscope, the probe's response can include ringing even with a coaxial connection to the probe.

author: bdunham7
author_rank: Super Contributor
timestamp: April 17, 2021, 03:57:57 pm
content: Quote from: jdutky on April 17, 2021, 08:00:13 amWell, it is ringing of a sort, but you aren't likely to see ringing due to ground lead inductance at that low of a frequency.

author: radiolistener
author_rank: Super Contributor
timestamp: April 17, 2021, 04:18:15 pm
content: Quote from: David Hess on April 17, 2021, 03:43:13 pmyes, the frequency response of a Chinese probes (which is usually included with 500-1000 USD oscilloscopes) is not flat and may be very terrible. Especially if you bought it on ebay or aliexpress for 10-20 USD as a "brand new 200 MHz probe".But the probe ringing effect can be caught at much higher frequencies, more than 1-10 MHz. At low frequency it's influence is too low to be noticeable.

author: David Hess
author_rank: Super Contributor
timestamp: April 17, 2021, 06:24:58 pm
content: Quote from: radiolistener on April 17, 2021, 04:18:15 pmSome probes are just defective by design.QuoteI agree.When the probe and oscilloscope bandwidth are the same, then the limited bandwidth of the oscilloscope will conceal the poor response of the probe above the probe's bandwidth, for the most part; it can still be observed with a good enough signal source for testing. When the probe's bandwidth is higher than the oscilloscope's bandwidth, then any aberrations in the probe's response are much higher and attenuated by the oscilloscope's more limited response even more.

author: Rick King
author_rank: Contributor
timestamp: April 18, 2021, 12:37:05 pm
content: Hi,I really appreciate all the information. I am kind of over my head; but that's how I learn.I can't always trust YouTube reviews because many of them get free stuff for doing the reviews. What I get here is real world experience. Not all Chinese made "stuff" is bad. Before I retired I worked for a US monitor company and we had some made in China; to our spec and parts with US inspectors.Keep in mind; as I said before, I am just experimenting and learning.I will say with my limited knowledge and thinking through what you guys have been saying; I made new cables to connect to the PC DAC. Tested the cables with a Fluke 115 RMS multimeter. I am getting very nice SINE waves and the SQUARE waves look much better depending on the frequency and TIME/DIV. At some point I will invest in a better signal generator.What I want to do is learn and to try a real world application because the extent of my use will be troubleshooting a manufactured component. Mostly vintage. My end goal is to work on this equipment and possibly sell some of them at a good price, but I can't sell something that may or may not work properly. It's not in me. I will only sell something that I know is working and would use myself. I'm having a hard time parting with some of them though (i.e. 1963 Sherwood S-2100 valve tube receiver). So I guess at some point I will need an RF signal generator??Keep it coming.RickP.S. I can't seem to figure out how to get reply notifications to the post; or any. I will go back to check my settings; again.

author: Rick King
author_rank: Contributor
timestamp: April 18, 2021, 12:39:57 pm
content: P.S.S. I reset notifications so will see if it works.

author: Rick King
author_rank: Contributor
timestamp: April 18, 2021, 12:56:28 pm
content: Here are the probes characteristics. The one on the left came with the scope. The one on the right (P6200) are the ones I bought.

author: tggzzz
author_rank: Super Contributor
timestamp: April 18, 2021, 01:30:05 pm
content: Quote from: Rick King on April 18, 2021, 12:37:05 pmI'm glad you are making progressGiven those two points, I strongly suggest you understand the "effective use" and "safety" refeerences inhttps://entertaininghacks.wordpress.com/library-2/scope-probe-reference-material/

author: Rick King
author_rank: Contributor
timestamp: April 18, 2021, 04:50:29 pm
content: Quote from: tggzzz on April 18, 2021, 01:30:05 pmI have started reading The Art of Electronics by Paul Horowitz & Winfield Hill. It's an older eBook version, but helpful. I would like to get the 3rd edition, but it's expensive. Oddly a used copy is more than the new hard book copy on Amazon.Rick

author: Rick King
author_rank: Contributor
timestamp: April 18, 2021, 07:04:46 pm
content: Hi,Sorry for so many questions.It's somewhat related to my topic. I made some cables to connect the PC signal generator to scope with braided wire. I'm curious; does this act like a coil and effect the signal; even though I securely welded the wires? Should I use a solid wire? If so, what gauge? I have 24 AWG solid with silicon insulation.Thank you.Rick

author: jdutky
author_rank: Regular Contributor
timestamp: April 19, 2021, 06:11:44 am
content: Quote from: Rick King on April 18, 2021, 12:37:05 pmjumping in over your head is a fine way to learn.QuoteThis is very true, and it's not even all that easy to triangulate off of multiple reviews because so many of them are for hire. EEVblog is a good honest source for reviews and information. The fundamentals videos are quite helpful if you are just learning this stuff. There are a couple other YouTube channels that I rely on for similar content:W2EAW is a ham radio operator who works for Tektronix and makes very informative videos,https://www.youtube.com/user/w2aewMr. Carlson's Lab is full of practical repair tips or working on vintage (usually tube) equipment,https://www.youtube.com/user/MrCarlsonsLabThe late Bob Pease, who wrote the Pease Porridge column for many years, also had a TV show, some of which are on YouTube athttps://www.youtube.com/user/andyaronsonnscThere are other good sources, but these are my most frequently visited, as they are full of so much information that I can't absorb it all in one viewing.Good luck and have fun.-- Jeff Dutky

author: tggzzz
author_rank: Super Contributor
timestamp: April 19, 2021, 09:23:16 am
content: Quote from: jdutky on April 19, 2021, 06:11:44 amProvided, of course, you don't damage equipment or yourself in the process. With high voltages and old equipment with "variable" chassis/earthing, that really cannot be ruled out.QuoteAs I told my daughter when we were doing things that could have killed us, "have fun - safely".

author: Rick King
author_rank: Contributor
timestamp: April 19, 2021, 02:16:17 pm
content: Quote from: tggzzz on April 19, 2021, 09:23:16 amI did purchase an anti-static wrist strap. I need to remember to use it. I also heard of the "one hand in back pocket"; so I end up working with my teeth. Oh; but then there is lead from solder; so the teeth are out. That just leaves my toes I guess. Haha

author: tggzzz
author_rank: Super Contributor
timestamp: April 19, 2021, 05:01:10 pm
content: Neither an antistatic wrist strap nor RCD will make you safe!