25 MHz Oscilloscope - Page 1
Forum section: electronics / beginners

author: n0b
author_rank: Contributor
timestamp: December 27, 2015, 11:09:31 pm
content: I found a 25 MHz analog oscilloscope on Ebay and I am wondering if 25 MHz is enough. I am only a beginner and just want to use the oscilloscope for measuring and I'm experimenting with this and would like to see how the circuits are behaving vs time.Thanks

author: tggzzz
author_rank: Super Contributor
timestamp: December 27, 2015, 11:47:27 pm
content: Yes it is sufficient, repeat, no it is insufficient. The answer depends on what you want to observe. Give us a clue about that and we will be able to give a more personalised answer.This question has been asked and answered many many times on this forum. Looking at the answers will help you understand what questions you need to ask and answer before we can help you more.In the absence of such info, it is worth noting that surplus 20MHz analogue scopes are commonplace. My local hackspace has more than it needs; yours might too.Only buy one if it is fully guaranteed and cheap.Any scope is better than none, but with a little imagination you can do a hell of a lot with a multimeter, some switches, a variable PSU, and some LEDs.The one area where an analogue scope is not sufficient is if you neet to observe one-off events; there a digital scope is highly beneficial.

author: Howardlong
author_rank: Super Contributor
timestamp: December 28, 2015, 12:58:52 am
content: Quote from: tggzzz on December 27, 2015, 11:47:27 pmIndeed, and learn a whole lot too.QuoteThat's true, except how did we ever manage without storage scopes? We forced non-repetitive things to be repetitive by setting up a test jig, and/or put marks on paper lined up on the scope graticule. Nowadays, even with an analogue scope you can capture single shot with a digital camera placed in front on a long exposure, and while hardly convenient, it would have been a godsend back in the 70s. Setting up a Polaroid shot was generally an prohibitively expensive undertaking for the home lab. Ah, those were the days.

author: vvv
author_rank: Newbie
timestamp: December 28, 2015, 01:00:14 am
content: Quote from: n0b on December 27, 2015, 11:09:31 pmAs tggzzz said, it depends. If you are just starting out with simple electronics it may be enough. It also depends on your budget. However even simple microcontrollers can be faster than 25Mhz, so there is something to be said about getting something you can grow into. Give us an example of what you are trying to experiment with and you will get a better answer. Maybe consider getting a 50Mhz or 100Mhz scope if you think you will continue with this hobby for a while

author: jpmkm
author_rank: Contributor
timestamp: December 28, 2015, 01:48:46 am
content: If it's cheap and this is your first scope, go for it. When you get to the point of needing more, you'll know.Just make sure the thing works properly(be wary of scopes that are sold "as is"). If you get a scope that's flaky and you're having problems, it can be hard to tell if it's with the scope itself, the circuit under test, or the user.

author: n0b
author_rank: Contributor
timestamp: December 28, 2015, 04:09:00 am
content: I appreciate the answers!It is a $70 scope, so I think I am going to reconsider, and find a different one. I am going to be working in electronics ( I hope ). I am just dipping my toes into FM radio and am building some transmitters and receivers that work just out of the FM band at about 97.7 MHz. So I think a 100 MHz scope would work better. But they are more expensive.P.SThe one thing is that I really like the layout of the one I am looking at. It is a BK Precision 2120bBut I have been looking at some Hitachi ones as well.

author: cponcsak
author_rank: Contributor
timestamp: December 28, 2015, 08:40:17 am
content: I think the general rule is to get a scope that has 5 times the needed bandwidth because the sample rate near the upper limits is almost useless.

author: tggzzz
author_rank: Super Contributor
timestamp: December 28, 2015, 11:06:31 am
content: Quote from: cponcsak on December 28, 2015, 08:40:17 amNo. Or rather you have to specify "needed bandwidth".In particular, if you are looking at a 1kHz digital output, a 5kHz scope won't be sufficient. Nor will a 25MHz scope if you want to see the edges and assess signal integrity.

author: tggzzz
author_rank: Super Contributor
timestamp: December 28, 2015, 11:12:08 am
content: Quote from: Howardlong on December 28, 2015, 12:58:52 amJust so, but some things can be difficult to make repetitive, e.g. PSU sequencing and turn-on transientsI always like forcing youngsters to think about how they could display a digital signal using only an analogue X-Y pen plotter with a sweep time of 10s and bandwidthe of (at best) a few Hz. No computers and no ADCs are allowed, because they aren't necessary - all you need are a few diodes and capacitors and resistors and transitors.

author: tggzzz
author_rank: Super Contributor
timestamp: December 28, 2015, 11:17:26 am
content: Quote from: n0b on December 28, 2015, 04:09:00 am$70 is expensive.If you are interested in radio in general and specifically in building transmitters, then a spectrum analyser would be more useful than a scope.Note that you have to beverycareful that your transmitter doesn't interfere with other people. A scope won't help you measure such effects. Get it wrong and you will be prosecuted, as it is a criminal offence in most jurisdictions.Strongly consider joining you local radio ham society - they will give you a lot of help and guidance and training.

author: n0b
author_rank: Contributor
timestamp: December 28, 2015, 06:30:15 pm
content: Yeah thanks for the warning, but I do understand about FM transmitting and how to transmit on an empty channel. Or a channel that is not on the public range. I actually have a neighbor that does HAM radio and he is a good friend of mine, so I will definitely talk to him.Again about the oscilloscope. I am not going to only use my oscilloscope for FM and radio but that is what I am doing currently. But if I find a cheap oscilloscope with sort of low bandwidth, say 30 - 60 MHz , I will probably buy it.One last thing about HAM radio. If I joined my local HAM Radio community would I have to buy a HAM radio or could I just go to the meetings or whatever they do. Never mind I will talk to my neighbor.Thanks

author: tggzzz
author_rank: Super Contributor
timestamp: December 28, 2015, 09:00:51 pm
content: Transmitting on an empty channel is the least of the problems. Talk to your neighbour about harmonics, intermod products, and as a sanity check, make sure you can explain how the IP2 and IP3 specs affect the output.You will see little of interest using a scope to look at an FM modulated RF carrier. You will see much more of interest using a $15 RTL-SDR either as a spectrum analyser or to demodulate the signal.

author: TimFox
author_rank: Super Contributor
timestamp: December 29, 2015, 03:13:09 pm
content: Even with audio circuits, sometimes 25 MHz is insufficient. With either solid-state or vacuum-tube circuits, oscillation above 100 MHz is always possible, and the circuit will not perform properly if oscillation is present.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: December 29, 2015, 04:55:33 pm
content: Nowadays, I'd consider something like a Tektronix 2213a as the _minimum_ analog scope for a beginner scoposcopist. Tek quality construction, 60 MHz bandwidth, 2 channels, basic delayed timebase, trigger capability and trace inversion/addition. And actually repairable if something goes wrong, with documentation and a lot of Tek parts easily available on the net.

author: Howardlong
author_rank: Super Contributor
timestamp: December 29, 2015, 05:02:07 pm
content: Quote from: tggzzz on December 28, 2015, 09:00:51 pm100% agreed, and SDR, although not calibrated, can be an invaluable tool in troubleshooting RF. A scope is usually the wrong tool for analysing RF, like trying to use a spanner as a chisel.

author: alsetalokin4017
author_rank: Super Contributor
timestamp: December 29, 2015, 09:19:17 pm
content: Quote from: Howardlong on December 29, 2015, 05:02:07 pmRight. A screwdriver makes a much better chisel than a spanner.(The flat kind, silly, not the pointy kind. Those are for drilling.)