Recommendations for a cheap 'scope

[MrBungle]

I’ve come to the conclusion myself that analogue scopes are great if you like fixing scopes. I like fixing scopes. However I don’t like when I have to fix scopes sometimes which is usually right in the middle of something. Ergo, new scope it was and that’s by necessity, digital. Most of the ooh ahh factor of analogue comes from instant response of controls and everything being there in your face. That’s makes you feel empowered.

However I can’t agree with any real advantage of analogue scopes other than price if I’m honest and if I was in a professional environment I probably wouldn’t touch one now. They are pretty useless when it comes to slow and rare events and they’re big liars. I use my scope most of the time for sweeping filters, capturing slow events and measuring transient response, something you just can’t do without eye gouging flicker or special phosphors or configuration or storage tubes on an analogue. The usual cases of watching a repetitive wave on an analogue scope is actually not all that good either. You’re seeing hundreds of them overlayed. The one time an odd one slips in, you can’t see it because it’s so dim. . You need crazy bandwidth and acceleration voltages to even capture rare events like that on an analogue scope leaving you with an expensive bill for an old 2465 or 485. The digital scopes allow you to see a window into an event. They’re a time machine and have the memory of an elephant. Scroll back 50us on a single triggered event after you’ve made your tea; yes please. I suspect that anyone who is brought up with modern digital scopes would find the old analogue ones frustrating.

[Bonky28]

Thanks everyone; quite a diversity of views!

Do I gather that something like this: http://www.ebay.co.uk/itm/DSO138-2-4...687MGNdY1VPq4A

is a complete waste of time?

Richard

[paulsherwin]

Not necessarily, but what are you planning to do with it? How would it help you to fix instability in a Hacker RP25 radio?

[Bonky28]

Good question. There's the rub...I don't know how to use one ...but am willing to learn...(and I like gadgets!). I have the Hacker manual that mentions using one- with a 'wobulator' and as I have a simple sig gen and multimeter (digital and an old Avo7) thought it could be another arrow in my quiver.

Perhaps I'm barking up the wrong tree... (Apologies for mixed metaphors)
Richard.

[Argus25]

Originally Posted by MrBungle

I suspect that anyone who is brought up with modern digital scopes would find the old analogue ones frustrating.

Well I wasn't brought up on digital scopes, but I have used them. Even the 100MHz ones are inferior to my 50MHz analog scopes for waveform reproduction.

You can see this easily when attempting to compensate a probe and the initial data that is missing on the digital scope after the fast rise. Sure if you want to capture and store waveforms and send them to your computer for a presentation, or do a math function on it, then go digital.

However, for looking at real waves in analog circuits, the analog scope is unbeatable. Take the Tek 2465B, they say its 400MHz bandwidth. It can actually display and lock, yes lock, a 900MHz waveform. While the amplitude info is meaningless you can still see it. Try that with a 400MHz bandwidth rated digital scope.

[Argus25]

..though I would be first to agree that digital scopes are superior to analog storage scopes for very slow or capture of infrequent data and for some multi-channel logic probe applications.

[Radio Wrangler]

Not a complete waste of time, you can learn things from this sort of kit, but when you start to use it for real, you quickly run into limitations.

Whether a scope is analogue, digital or whatever, it needs good attenuators to handle the range of input voltage it will meet. It needs high impedance input amplifiers with the necessary bandwidth and low enough capacitance to match scope probes... you'll use scope probes a lot.

The digital-scope-in-a-dongle or on one board things miss out badly in this area.

If you choose new, then a basic Rigol is probably the first worthwhile step on the ladder.

There are things digital scopes can do which analogue ones are incapable of, but there are things the other way round too. I use both types. They cover each other's blind spots.

Digital scopes sample the signal as a series of little snapshots. This can impose unreal patterns on the displayed signal called sampling artefacts and aliases. It can make signals appear to have a completely misleading timescale. To use one properly, you have to take precautions to find the real signal and not be mislead by an alias.

I spent 30+ years at HP as senior design engineer, designing spectrum analysers, sig gens, noise figure analysers, loads of telecomms stuff - and one 500MHz digital oscilloscope! It was good fun, and I've got fairly good knowledge of what goes on inside most test gear.

On the bench at home is a Tektronix 465B 100MHz scope (with one for spares in the attic) I switch it around with an HP1740A, its chief competitor, for a bit of variety. These are all complex instruments but £80 was the most expensive. There's a Tek digital one on the dining table, connected to a dismantled Icom IC765 transceiver.

David

[G0HZU_JMR]

However, for looking at real waves in analog circuits, the analog scope is unbeatable. Take the Tek 2465B, they say its 400MHz bandwidth. It can actually display and lock, yes lock, a 900MHz waveform. While the amplitude info is meaningless you can still see it. Try that with a 400MHz bandwidth rated digital scope.

Many scopes with a Gaussian front end response will be able to see up to three times the rated BW at reduced amplitude. So if the (400MHz BW) digital scope has a Gaussian response then I'd expect it to be able to easily display the 900MHz waveform provided the operator set it up correctly to make the measurement. Obviously, it will be at reduced amplitude. However, some digital scopes have a different type of front end filter that is much more like a brickwall but this is a tradeoff wrt sampling rate and alias response.

Getting back to general radio/hobby use I think it is crazy to spend more than about £50 on an analogue scope today in the UK. Most of the ones available will be old and tired and tinkered with inside. That's why it's best to try and find something like a surplus Hameg scope that might not be so old. Even 30 years ago many hobbyists who bought a used scope actually bought someone else's problems... eg you would often hear radio hams say they had bought a scope at a rally but they then listed all the niggly faults they had already found with it.

Analogue scopes often lead a hard life and the controls need to be rugged because there are so many controls that need to be adjusted for every measurement. In my experience the only brands I found that could survive intensive use in a busy lab were Tek, Iwatsu and Hameg.

[MrBungle]

The newer digital scopes have anti-aliasing filters (stochastic sampling) and heuristics for defining sample rates to avoid this so aliasing is rarely a problem any more. I haven't seen aliasing problems for a number of years. If you look at how the digital scopes work, they overlay samples and support averaging to give the same appearance as an analogue scope. You just have to press the right buttons!

[cmjones01]

Originally Posted by Bonky28

Do I gather that something like this: http://www.ebay.co.uk/itm/DSO138-2-4...687MGNdY1VPq4A

is a complete waste of time?

Building the kit will probably be fun and satisfying, but the result will be a really inconvenient and annoying scope. It would be pretty much useless for fixing radios. Not recommended.

Regarding the analogue/digital debate, I find that bad digital scopes (and I've used some shockers) make me wish I was using an analogue one. Good digital scopes are great and can do the job of an analogue one, but they're expensive for a hobbyist.

Chris

[Nickthedentist]

I would ask whether anyone here has a straightforward, working, reliable, analogue scope they could sell you for, say, under £50, and see whether you get any responses.

[cmjones01]

Good call.

Chris

[Bonky28]

Hi again everyone; many thanks. I have been offered a scope but the present owner lives in Glasgow and would wish for it to be collected in person. I live in Sheffield(!)
Is anyone travelling in the vicinities? I don't mind paying a contribution towards fuel etc.
Thanks,
Richard

[Radio Wrangler]

There's a thread on this group for transport wanted/offered and people check for anything they can help with before a journey. It's what is meant by the "Forum Courier Service" and people are much more careful with stuff than any courier firm.

I just drove down from Fife to Huddersfield on Friday and if I'd known, I could have put a couple of different scopes in the car to show you what they can do and how to drive them. Hands-on one-to-one driving lessons can't be beaten.

David

I would avoid a digital scope as a first instrument

So would I unless you can afford a really good digital one (excluded by the title) which, ironically try to emulate analogue 'scopes. Learn on a proper analogue 'scope then a much cheaper digital one would be understood and take up a lot less bench space.

And as to the original question, any 'scope will work for most day to day stuff.

[high_vacuum_house]

My first oscilloscope was a basic 20Mhz analogue 2 channel model that my dad bought from Maplin in a sale. It is a Topward brand and was ideal learning tool for basic op amp and simple transistor amplifier theory.

With a Maplin function generator kit as well it became significantly more useful and my dad taught me LC filter theory and design with them.

Depending on what you want to do a sine/square/triangle function generator will compliment an oscilloscope well as it produces a stable signal which is easier to follow than a constantly changing signal.

Certainly good probes are a must for anything more than a few MHz

The Philips PM 3xxx series of oscilloscopes are very good 2 channel analogue models that are robust and the controls are well laid out and shouldn't give problems driving them.
I have a good working one which I bought with probes and a manual for £30

Christopher Capener

[julie_m]

I just ordered one of those eBay kits, purely for interest's sake.

By the time it arrives on the slow boat from China, I probably will have forgotten all about it, so it should be a nice surprise .....

[Al (astral highway)]

Originally Posted by Bonky28

I like trying to repair Hacker radios. I have a sig get but no 'scope.

I have to agree with those who wonder why a 'scope is needed to repair most radios? I do own one but I use it for project work, never need to for radio or audio repair.

[MrBungle]

Originally Posted by julie_m

I just ordered one of those eBay kits, purely for interest's sake.

By the time it arrives on the slow boat from China, I probably will have forgotten all about it, so it should be a nice surprise .....

To quote someone I know who bought one, he went: "ooh, ahh, oh it's broken"

[Bonky28]

Originally Posted by Radio Wrangler

There's a thread on this group for transport wanted/offered and people check for anything they can help with before a journey. It's what is meant by the "Forum Courier Service" and people are much more careful with stuff than any courier firm.

I just drove down from Fife to Huddersfield on Friday and if I'd known, I could have put a couple of different scopes in the car to show you what they can do and how to drive them. Hands-on one-to-one driving lessons can't be beaten.

David

Thanks David, I'll investigate

BW

Richard