Question from a beginner

[anastienx]

I'm about to buy a new oscilloscope, I understand the meaning of the basic parameters,  but I don't know how many say samples/second the best when compare.
I think I'll buy one of these:
 Tektronix TDS 420A
http://www.ebay.com/itm/271963973518?_trksid=p2050601.m570.l5011&_trkparms=gh1g%3DI271963973518.N26.S2.M-7051.R4.TR4&autorefresh=true
it is free shipping and near to my country.
or I may buy Rigol from china, no local available.
does the extra sample/second worth it, and how is that TDS 420A?

[Galenbo]

I'm about to buy a new oscilloscope,... Tektronix TDS 420A... Rigol

If you really are a beginner, It's maybe the best choice to just follow the masses, and buy the new Rigol, like everybody else.
There will be plenty of videos on internet, tests based on that model, tricks, howto, and even repair info if you blow it up.

With all this new DS1054Z can do, and the low price, I really don't see a reason to buy a used scope anymore.
(except if you can have it for 20 euro, or if you want the specs from a device worth 10K)

[jitter]

Tektronix TDS 420A

Oh no, not one of those. We used to have these at work and I never ever liked using them. I wouldn't pay $ 50 for it. I'd rather get a good analogue scope instead (but I bought a Rigol).

[max666]

I'm about to buy a new oscilloscope, I understand the meaning of the basic parameters,  but I don't know how many say samples/second the best when compare.
...

The sampling rate tells you how many measurements are acquired per second. Now your sampling rate needs to be at least double the bandwidth, or you may start to see things that aren't there:

Fig. 3: The samples of two sine waves can be identical, when at least one of them is at a frequency above half the sample rate. [Sauce]

So I'm actually baffled at that Tektronix scope not complying with the sampling theorem. That scope should actually only be usable for signals up to 50 MHz, or am I missing something here? 
And in light of that I too would recommend the DS1054Z, so many features I wouldn't wanna miss, and $350 is to much for the Tektronix. A cheap analog scope is certainly a good option for a beginner, but if you are willing to pay as much as $350, then save up for a DS1054Z.

[Fat]

I bought a Rigol about a year ago, entry model DS1102E. Wish I'd gotten the Z model.  Great scope for us beginners and pretty easy to use.  I did pick up a third hand Tektronics 2245 for $20.00 a few weeks ago.  It works ok and is fun to use, but it takes a LOT of workbench space.  I use the Rigol the most.  If I was doing it again, I'd make my first scope an entry Rigol and leave the old scopes alone.

Fat

[jitter]

I'm about to buy a new oscilloscope, I understand the meaning of the basic parameters,  but I don't know how many say samples/second the best when compare.
...

The sampling rate tells you how many measurements are acquired per second. Now your sampling rate needs to be at least double the bandwidth, or you may start to see things that aren't there:

Fig. 3: The samples of two sine waves can be identical, when at least one of them is at a frequency above half the sample rate. [Sauce]

So I'm actually baffled at that Tektronix scope not complying with the sampling theorem. That scope should actually only be usable for signals up to 50 MHz, or am I missing something here? 
And in light of that I too would recommend the DS1054Z, so many features I wouldn't wanna miss, and $350 is to much for the Tektronix. A cheap analog scope is certainly a good option for a beginner, but if you are willing to pay as much as $350, then save up for a DS1054Z.

Yeah, I wondered about that too, 200 MHz bandwidth from a 100 MS/s scope?

Here's how they do it.

Edit: here a vid that shows how a 100 MHz sineswave is displayed. Look at how long it takes to construct that wave (just skip through a bit, the power on takes an eternity  ).

[max666]

Ah, yes, they to equivalent time sampling. Thanks
Tektronix should have put a huge asterisk behind that 200 MHz!

[oldway]

Yeah, I wondered about that too, 200 MHz bandwidth from a 100 MS/s scope?

Here's how they do it.

Edit: here a vid that shows how a 100 MHz sineswave is displayed. Look at how long it takes to construct that wave (just skip through a bit, the power on takes an eternity  ).

What a piece of shit !
My old analog 2235 is 1000 x better

[Wim_L]

That's an awfully noisy incoming sine wave, or that scope is broken. Equivalent time sampling has its flaws, but when working properly it should give a much cleaner picture than what you see in the video.

[jitter]

That's why I said "oh no". This is what you can expect from these oldies lack of computing power (when compared to modern day scopes)...

[Wim_L]

True, those old digital scopes aren't the most convenient things to use. However, this is far worse than typical expected performance.

Note the warning next to the frequency measurement on the right side of the screen: "Unstable histogram". I'm guessing there's excessive trigger jitter, either because of a defect inside the scope, or because the incoming signal is too noisy (in that case, the HF reject triggering mode would help if that model has it). The display looks like what you'd expect for an equivalent time sampled sine wave in the presence of an unstable trigger signal.

[max666]

In any case I think this nicely demonstrates that equivalent time sampling is not something you want in a beginner scope.
Not every signal can be viewed at with equivalent time sampling, and you would have to know an awful lot about a signal beforehand to make sense of what you see on the screen.

[tggzzz]

In any case I think this nicely demonstrates that equivalent time sampling is not something you want in a beginner scope.

Probably not, unless their budget and the signals they are looking at make it a good option.

Not every signal can be viewed at with equivalent time sampling, and you would have to know an awful lot about a signal beforehand to make sense of what you see on the screen.

You certainly need repetitive signals, but the latter statement isn't always true. Personally I like scopes that display each individual point as it is measured; you start out with a very sparse display and then the details gradually emerge.

But then 25 years ago I was using a 25MS/s 1GHz boat anchor to look at sub-nanosecond risetimes - very useful and easy to use.