[sdiy] Oscilloscope on a Budget 200

[Richie Burnett]

>> Some of the cheap Chinese copycat models will quite happily show you a 
>> 20MHz signal as a 1kHz signal if you have the timebase set to 100us/div. 
>> That really confuses students (>.<)

> and if it doesn’t confuse the user at least she or he loses time when 
> ruling out artifacts.

*Exactly*  It ultimately comes down to a question of how much your time is 
worth?  If you're doing hobby stuff for fun and have plenty of time to learn 
about aliasing and artefacts then by all means get something cheap and get 
cracking.  But if you are running a business with products to get out the 
door and deadlines to meet, (or have very limited hobby time but a bit of 
spare cash,) then it's worth buying the best that you can afford.

> I’m not looking for something cheap but rather affordable (seeing that as 
> an investment).

What do you class as affordable?

> I remember Tim Stinchcombe bringing his TDS 210 to Cambridge, which is not 
> a handheld but a lot more portable.

The TDS210 is nice, but quite old now.  You can probably pick up later Tek 
TDS1000  and TDS2000 series units second-hand now, and they are more capable 
scopes.

>> Conversely the likes of Agilent and Tektronics either show a nice shaded 
>> smudge of HF, or filter it out completely, but never undersampled.

> What would you prefer? Filtering?

I am a fan of HP / Agilent or whatever they're calling themselves this week.

I've got a DSO6034A on my bench which I think is excellent even though it's 
nearly ten years old now.  It's quite a high spec but I do a lot of work at 
MHz frequencies, and it is essential to my livelihood.  Models with less 
channels and less bandwidth will be cheaper, and can probably even be picked 
up second-hand now too.  (In the ten years that I've had it, I've only 
encountered one tiny bug in the firmware, where it very occasionally powers 
up with the 50-ohm termination enabled on one of the channels, and you have 
to unplug the probe and reconnect it for the termination to switch off!)

A few years ago I compared Agilent's current offerings with Tektronix in the 
same price range, and felt that Agilent had the edge in three areas:

1. More responsive user interface.  The Tek user interface at the time felt 
under-powered and laggy.  Not so much of a problem for a newbie finding 
their way around, but frustrating for anyone who knows their way around a 
scope and makes quick adjustments to controls, if the display takes a while 
to catch up.

2. More features built-in for the price.  The Agilent scope had most maths 
features like FFT built-in, where they cost extra money for the same 
features on the equivalent Tek models.  (These days even the cheap Chinese 
models usually have the maths features built-in!)

3. Better anti-alias filtering and more intuitive display of "difficult 
waveforms".  Things like looking for runt pulses or corrupted data that only 
happens every once in a while.

These days the swing might be back towards Tek or even LeCroy might have a 
more budget offering?

-Richie,