Yeah, I see what you mean about the ‘want’ and ‘know’ etc. There’s definitely a bit too much describing things as a decisions, negotiation or communication for my tastes. That might just reflect having learned about this stuff in a much drier format at University, though, and if it helps with making the topic more approachable then that’s all for the better, I guess.
It’s an impressive amount of work to go through and collect the data for all of this visualisation, though, and it has enough noise and other real-world effects to be very obviously real-world data. It seems like the whole thing could probably be demonstrated a lot more cleanly using or overlaying the theoretical transmission line mathematics, though.
The other thing is that he doesn’t seem to mention the magnetic field/inductance effect all that much. Realistically everything he’s showing is a factor of two dominant ‘parasitic’ effects, the inductance of the circuit and the capacitance of the circuit. The other factor is that these are not a lumped element anywhere, but occur incrementally along the length.
The way this was taught at university is that with a transmission line, you can essentially consider the entire thing as the integral of a bunch of infinitely short segments. The inductance and capacitance are both linear with length, so the ratio between the two is always the same. That ratio is what gets used to calculate the characteristic impedance of the transmission line. If you ever see an impedance for a transmission line like 50 ohm, 75 ohm or 300 ohm, that’s the characteristic impedance. As the inductance of the transmission line increases relative to the capacitance, the impedance gets higher and vice versa. That impedance doesn’t have a whole lot of use in DC environments like demonstrated there, but it’s super important when it comes to AC signals. Having a load that is ‘matched’ to the transmission line means that there are none of the reflected effects that he is demonstrating. If the load is too low impedance vs the characteristic impedance, you get a version of what he showed on the shorted end of the branch while if the load is too high, you get a version of what he showed on the opened end. The difference with an AC signal is that it’s always happening constantly.
It can also get pretty gnarly. If you’re talking about high power transmission, you might have a few hundred volts or even a few kV in the transmission line. If the load isn’t matched or gets disconnected, that reflected wave means that you’ll get voltages along the line that are twice what they should be, which can lead to catastrophic transmitter failure or even the transmission line itself failing and catching fire etc. Fun stuff.
In his defense, I think the video is approachable for anyone and high level engineering classes aren’t (I have a master’s in EE from CSM, but I haven’t used it). He also has some other videos about impedance matching (which I haven’t watched yet). I also thought the exaggerated electron simulation really showed what was happening best. That connected the Ohm’s law and impedance model to something tangible for me.
Oh for sure, that’s why I commented that my distaste may reflect the way I was taught it. Ultimately, if it helps someone understand the concept then that’s good. I just think it could remain equally as approachable with different and ‘less mystical’ phrasing, for lack of a better description.
Yeah, the exaggerated electron display is a good way to do it. It’s also nice because it’s an exaggeration of the effect that still matches the actual situation pretty well.
Interesting looking option if you need something small/portable. The specs are pretty mediocre, though, but fair for the price I guess. 4k samples and 15MHz bandwidth is very much on the bottom end of performance. At $150 USD I’d say it’s at a weird point. It’s a decent chunk of money for something with relatively poor performance. The open source application layer sounds interesting, but without knowing how much that’s supported then I’m not sure I’d personally see any use for it.
Compared to a GDS-1054B which can apparently be found for $300 on special and is 50MHz with 4 analog channels, 10Mpt memory and a more standard interface.
Or the Siglent SDS1052D which is $240 on special at the moment on Amazon and is 50MHz, 2 channel, 32k point (still a bit low, imo) and has a more standard interface.
Those 2 options seem like a LOT more capability for the money, to me.
I’ve had this one in my amazon cart for a long time after watching this video
But I go back and forth about whether I REEAAAALLLY need it for what I do…So I keep going back to these $30 portable small ones, but just end it never buying any lol
That looks pretty reasonable, actually. I had a friend who bought a similar one and found it was kinda terrible due to a poor waveform capture rate so I’d check that spec first, but everything else looks good.
Are these ones obsolete now. They are always up for auction and go for around 100.00 to 300.00 Canadian. Check your local government auction sites.
A guy at work has a hantek unit that seems to work pretty good for a hand held unit.
Yeah, unfortunately. It’s essentially the difference between an old analog radio and a modern smart phone. They’re technically doing the same job in some cases but the technology has advanced SO much that the $300-500 new scopes discussed above are likely better in almost every single way to a scope that was $10-20k when I started into the industry and better than anything that could even really be imagined 40-50 years ago, money be damned.
There are still areas where the cheaper scopes discussed here take massive shortcuts. Typically they have poor sensitivity and high noise on the inputs, along with poor common-mode rejection. That makes life difficult if you’re looking at small analog signals. Most people are going to find the advantages of a modern scope significantly more helpful than the minor disadvantages listed here.
The build quality will also likely be much worse, along with the quality of the probes etc. All of that will be better in older 2nd hand gear, most likely, but those aren’t the things that are going to be valuable to someone for a hobby workshop type scenario.
If you’re in the market for one, at that kind of price range I’d be going with the Hantek that Mike M posted above, but my extremely biased recommendation would be to spend a little more and get something similar from a slightly more well known brand like Siglent, Rigol or GW Instek, in that order. The Siglent stuff is extremely well regarded at this level as well as being easily software unlocked for significantly higher capability.
