Tek 2445 for TDS 1002?

[Kevin Hope]

I am considering trading in my Tek 2445 analog oscilloscope for a
digital one in the TDS 1000 series.

Basically for size and weight savings, as well as direct readouts and
FFT.

Most of the work I do is audio, but sometimes employ 200-300V for tube
work.

I assume others may have gone this way. Could I have a few opinions,
even if on anlog vs. digital in general?

What, if any, limitations would I notice in making this change?

Thank you very much,

Kevin Hope

 

[Phil Allison]

"Kevin Hope"

I am considering trading in my Tek 2445 analog oscilloscope for a
digital one in the TDS 1000 series.

Basically for size and weight savings, as well as direct readouts and
FFT.

Most of the work I do is audio, but sometimes employ 200-300V for tube
work.

I assume others may have gone this way. Could I have a few opinions,
even if on anlog vs. digital in general?

What, if any, limitations would I notice in making this change?

** I strongly advice you to KEEP your analogue scope !!

For audio work and other general analogue work, they are far superior.

Analogue scopes are intuitive to operate, present all waveforms in REAL
time, the bandwidth is fixed instead of changing with the time base setting,
there is no aliasing to drive you nuts and most of all, the CRT trace gives
far more detail, resolution and information about a waveform than an LCD
screen.

Obviously, a good digital scope can do things an analogue cannot (and vice
versa) - so owning one of each is best particularly if you need waveform
capture, signal averaging or on screen measurements of time and voltage etc.

A colleague loaned me his Tek TDS210 scope a while back, for a test drive
for a week or so. I honesty tried *very* hard to get used to it - but to
no avail.

The image quality on the LCD screen was, IMO, appalling. Known clean sine
waves always looked to be infected with noise and even crossover like
distortion artefacts. It was many times slower to use due to constantly
having to fiddle with the settings and I regularly had to go back to my
usual 50MHz analogue scope to check if what I was seeing was for real. Most
often is wasn't.

Having spent nearly 40 years using and trusting ( therefore acting
immediately upon ) what I saw on the screen of a scope, I found what the
TDS 210 was showing me was not at all trustworthy for my purpose - audio
design & servicing.

You mileage may vary, but do try to get a "test drive" for a least a few
days on *actual work* BEFORE laying your dollars down or parting with that
lovely analogue scope.




......... Phil

 

[Paul Mathews]

I am considering trading in my Tek 2445 analog oscilloscope for a
digital one in the TDS 1000 series.

Basically for size and weight savings, as well as direct readouts and
FFT.

Most of the work I do is audio, but sometimes employ 200-300V for tube
work.

I assume others may have gone this way. Could I have a few opinions,
even if on anlog vs. digital in general?

What, if any, limitations would I notice in making this change?

Thank you very much,

Kevin Hope

If you ever need good common mode rejection, you'll be much happier
with TDS3000 series. The bottom-end DSOs from Tek don't seem to have
much CMRR. Good deals can be found on older TDS3012s, for example.

I switched to DSOs as soon as sampling rates of a gigahertz and higher
became available at a reasonable cost, and I'd never go back to analog
now. A lot of the opinions you'll read are based on experiences with
sampling rates of a few 10s of MHz, where aliasing can be a real
problem. I kept an analog scope for a few yrs, but never used it, so
sold it before it became totally valueless.
One other thought: If you do low-level signal work, in the millivolts
and below, then there's definitely still a place for analog scopes,
also.
Paul Mathews

 

[Phil Allison]

"Paul Mathews"

A lot of the opinions you'll read are based on experiences with
sampling rates of a few 10s of MHz, where aliasing can be a real
problem.

** Really ?

The TDS 1002 scope is virtually the same as the TDS 210 that I "road
tested".

Ailiasing is a major problem despite the advertised 1 GS/s spec.

The reason is simple and given in the operator's manual.

When set for 5 milliseconds per division, the actual sampling rate is only
50kS/s.

So ailiasing starts at 25 kHz.

Big problem.



.......... Phil

 

[Richard Freeman]

"Kevin Hope"


** I strongly advice you to KEEP your analogue scope !!

For audio work and other general analogue work, they are far superior.

Analogue scopes are intuitive to operate, present all waveforms in REAL
time, the bandwidth is fixed instead of changing with the time base
setting, there is no aliasing to drive you nuts and most of all, the CRT
trace gives far more detail, resolution and information about a waveform
than an LCD screen.

Obviously, a good digital scope can do things an analogue cannot (and vice
versa) - so owning one of each is best particularly if you need waveform
capture, signal averaging or on screen measurements of time and voltage
etc.

Look I have to agree with Phil, DSO's do feel quite different to an Analog
scope I have both and tend to use the DSO more as a portable (it is a TDS210
and is lightweight and easy to carry), where I need to capture waveforms,
where I want to look at what happens before a trigger and other odds and
ends like that and use an Analogue for most other work.

Bear in mind that a DSO can give you aliasing problems as the Sample rate
does vary with the sweep speed - In fact the Users manual for the TDS 1002
specifcally has a section on this issue (Download the Manual for the TDS1000
and 2000 from the Tektronix website pages 20 to 23 deal specifically with
aliasing).
I have to admit that even though I am familiar with aliasing it has still
caught me out on occasion even though I have by and large developed the
habit of double checking signals at different sweep speeds to get around
aliasing

Of course DSO's do have their uses and the capture facility is great for
looking at non repetitive events such as pulses and digital signals
(although I also tend to use a logic analyser when I am getting into more
detail with Digital issues) and if you can get used to there quirks they can
do a fine job. But you do need to remember that a DSO is a different Beast
to an Analogue scope and does handle things differently. in fact the DSOs
real strength is in its storage capability and the Persistance mode can be
quite usefeul for comparing repetitive waveforms.

If you are used to an Analog scope then For goodness sake do not go out and
swap your analog scope for a Digital one - it will probably drive you
insane.

If you have uses for a DSO and are used to an Analog one then I suggest you
do what I do and have both - You can make your mind up later which one you
prefer if you only want to keep one but do not commit to a DSO until you are
used to one and by this I mean have used one for a while not just bought one
home and plugged it in.
Might I also suggest if you wish to go Digital that you try some of the DRT
(Digital Real Time ) Scopes as they do have more of an Analog feel than the
normal DSOs - although they do still have aliasing issues etc and I strongly
recommend that you get used to one before you replace your analog scope.

Regards
Richard Freeman

 

[Paul Mathews]

"Paul Mathews"


** Really ?

The TDS 1002 scope is virtually the same as the TDS 210 that I "road
tested".

Ailiasing is a major problem despite the advertised 1 GS/s spec.

The reason is simple and given in the operator's manual.

When set for 5 milliseconds per division, the actual sampling rate is only
50kS/s.

So ailiasing starts at 25 kHz.

Big problem.



......... Phil

Hmm. Let's see. 5ms/div, choosing 20kHz (to make the arithmetic easy)
each cycle occupies 50us/5ms/div = .01 divisions. So, on you analog
scope at 5ms/div, any 20kHz content shows up as a blur, and you need to
switch to a faster timebase to see it. The same thing is true for a
DSO. The limitation, for the analog scope, is mostly trace width. For
the DSO, it's the number of points they show on the screen, not the
sampling rate per se. I had a TDS210 about 10 yrs ago, and found it
very useful, within its limitations, which is exactly how I'd describe
any instrument I use. The wise DSO user always views the signal at a
variety of timebase settings, just to make sure that he/she understands
what's really going on with a waveform, and the same is true for analog
scopes. Is that just a blur, or is there high frequency content?
Paul Mathews

 

[Nico Coesel]

"Paul Mathews"


** Really ?

The TDS 1002 scope is virtually the same as the TDS 210 that I "road
tested".

Ailiasing is a major problem despite the advertised 1 GS/s spec.

The reason is simple and given in the operator's manual.

When set for 5 milliseconds per division, the actual sampling rate is only
50kS/s.

So ailiasing starts at 25 kHz.

Big problem.

Yes indeed, it sounds plain stupid to build an oscilloscope that way.
Is Tektronix cutting corners? Nowadays you can expect a digital
oscilloscope to have enough memory to store at least 1M points so
lowering the sampling rate only occurs at very low time/div. settings
(which should change the anti-aliasing filter accordingly). IIRC the
54 series HP / Agilent oscilloscopes work that way.

 

[Jim Yanik]

[email protected] (Nico Coesel) wrote in

Yes indeed, it sounds plain stupid to build an oscilloscope that way.
Is Tektronix cutting corners? Nowadays you can expect a digital
oscilloscope to have enough memory to store at least 1M points so
lowering the sampling rate only occurs at very low time/div. settings
(which should change the anti-aliasing filter accordingly). IIRC the
54 series HP / Agilent oscilloscopes work that way.

I suspect that the HP/Agilent 54 series isn't priced as low as the TEK
TDS1002,nor are they in the same general class of instrument.

 

[Phil Allison]

"Paul Mathews"

Hmm. Let's see.

** Here come a whole pile of smartasre bullshit for sure.......

5ms/div, choosing 20kHz (to make the arithmetic easy)
each cycle occupies 50us/5ms/div = .01 divisions. So, on you analog
scope at 5ms/div, any 20kHz content shows up as a blur, and you need to
switch to a faster timebase to see it.

** Not a blur - but very fine detail that is obviously a high frequency
signal superimposed.

The context of the measurement task makes the user aware if the HF is as
intended or not.

The same thing is true for a DSO.

** WRONG:

What do this clown think ailiasing is?

The limitation, for the analog scope, is mostly trace width.
For the DSO, it's the number of points they show on the screen, not the
sampling rate per se.

** Go read my reply to the OP - this time carefully.

I hit each of these matters hard.

I had a TDS210 about 10 yrs ago, and found it
very useful, within its limitations,

** Utterly meaningless.

The wise DSO user always views the signal at a
variety of timebase settings,

** How fucking tedious.

A service tech trying to make an income cannot afford time wasted by a scope
that shows him trash - making faultless items seem to be full of faults.

just to make sure that he/she understands
what's really going on with a waveform, and the same is true for analog
scopes. Is that just a blur, or is there high frequency content?

** Utter bullshit.

Analogue scopes do not produce ailiasing.

The useful bandwidth is not a function of the time base setting.

The trace is sharp and clean and reveals far more info than a grainy LCD
screen ever can.




........ Phil

 

[Paul Mathews]

[email protected] (Nico Coesel) wrote in


I suspect that the HP/Agilent 54 series isn't priced as low as the TEK
TDS1002,nor are they in the same general class of instrument.

--
Jim Yanik
jyanik
at
kua.net

Actually, it has more to do with the number of pixels available in the
LCD than with the amount of available memory. I stand by my comments,
and I have access to a great variety of scope models from Tek, Agilent,
and LeCroy. I also have written many DSP applications. Most modern DSOs
save so much time, that it's no real inconvenience to double-check for
possible aliasing in new situations.
Paul Mathews

 

[Phil Allison]

"Paul Mathews"

I also have written many DSP applications.

Most modern DSOs
save so much time, that it's no real inconvenience to double-check for
possible aliasing in new situations.

** Another "know all" code scribbler - who has totally failed to
comprehend the significance of that fact the OP specified he worked on audio
and tube gear.

Likely never seen any.



........ Phil

 

[tekamn]

Absolutely correct Paul, that's the point: choosing 20kHz (to make the
arithmetic easy)
each cycle occupies 50us/5ms/div = .01 divisions.

I have the 2465B handy, but for low frequency (audio gear and tube
work), I have had no case where it was necessary to have so much BW.

The DSOs like TDS, etc. are nice for audio, for single events and in
genral if you have to document stuff: interfacing to a PC or laptop is
easily done.

Like with all technical gear, one has to know *how* to use the
different scopes - and most of us needed some time to get the change
from analogue scope to DSO and feel well with it.

Some of us will never make it ;-)



just my 2 cts. of opinion


hth,
Andreas

 

[tekamn]

It a different class of scopes. Not even the analogue to digital
features. Also the "look & feel" of the handling.

Downloading & studying the tektronix "abc of oscilloscopes" helped me a
lot to understand Teks philosophy and get used to the scopes from
Tektronix. Maybe it is helpful for you too.


hth,
Andreas

 

[Phil Hobbs]

The wise DSO user always views the signal at a
variety of timebase settings, just to make sure that he/she understands
what's really going on with a waveform, and the same is true for analog
scopes. Is that just a blur, or is there high frequency content?

The wise user almost never takes the scope out of "envelope" mode, which
in my scopes runs the digitizer at full speed and plots a vertical
line from the highest to lowest values within one display pixel. While
this smears out the signal slightly in the vertical direction, it's
otherwise very much like using an analog scope that can look backwards
in time. Aliasing is not a major problem, and you get an accurate
indication of the limits of the measurement resolution.

I've seen too many strange waveforms that turned out to be caused by
some nasty tarting-up algorithm inside the scope.

Cheers,

Phil Hobbs

 

[Nico Coesel]

"Paul Mathews"


** Another "know all" code scribbler - who has totally failed to
comprehend the significance of that fact the OP specified he worked on audio
and tube gear.

A DSO is very usefull for low frequencies. You'll have a stable
flicker-free picture.

 

[Phil Allison]

"Nico Coesel"

A DSO is very usefull for low frequencies. You'll have a stable
flicker-free picture.

** No problems in the audio band .

Still very usable down to 5 Hz and less with a standard persistence screen.



.......... Phil