RLC bridge

Not so--all you need is to choose a slow sweep speed. Peak detect or envelope mode will show you the problem, but IME most digital scopes alias massively in sample mode.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

Not really. Except for the big Hamegs and some others the scopes have a very limited sample memory. As low as 4k with some Tek scopes. So the sample rate is ratcheted down as you increase the time base.

Even the expensive DSOs are too great there.

:-)

--
Regards, Joerg

http://www.analogconsultants.com/

waveform.

record it on tape too.

phenomenal

What for? In those days video storage was prohibitively expensive. The only places that had it were a few high schools and the police.

version.

Do they even speak Dutch up there in Friesland? :-)

--
Regards, Joerg

http://www.analogconsultants.com/

Oh alright. I guess I'm assuming that even our newbie 'scope operator knows to set a sweep speed more-or-less comparable to the frequency of the signal he's measuring.

E.g., trying out a few scopes here...

Say I think my signal is "around" 10Hz -- in that case, a 1 second (or faster) sweep seems "reasonable." At that sweep rate, a Tek DPO4104

1GHz scope samples at 10ksps and a LeCroy 540Zi 4GHz scope samples at 250ksps (with all the scope settings at their defaults). Hence, to see aliasing on the Tek you need a signal at least 5kHz, and at least 12.5kHz on the LeCroy. The later there is an order of magnitude better than what you "thought" your signal was -- if you're that unsure of what the signal should look like then you should start out with very fast sweep and gradually reduce it, or enable peak-detect/envelope mode to force the scopes to increase their sample rates.

That technique might not be something a newbie would know, but it still seems to me their chance of making a poor measurement on an analog scope is about on par.

Or were you thinking our newbie is going to take something like a pulser with a very fast edge rate -- but potentially slow repetition rate -- and feed it into a DSO set to a slow sweep? That could certainly create some confusion. :-)

I noticed that Rohde & Schwarz own up to their ENOBs right on their product flyer; that's pretty respectable at least.

Not as a true network analyzer. But it's in line with what the SR720 will do.

--
Paul Hovnanian     mailto:Paul@Hovnanian.com
------------------------------------------------------------------
Optimist:  "The glass is half-full."
Pessimist: "The glass is half-empty."
Engineer:  "The glass is twice as big as it needs to be."

All the newbie needs is for his emitter follower to start oscillating, and he'll very likely need a sweep speed 50 or 100 times faster than he expects.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

No, newbie is most likely staring at all those buttons, doesn't have the foggiest what most of them are for, then presses the one that has a unique color and where the text on it promises the most relief: Auto-Set.

On analog scopes I have seen most people only having difficulties with the fancier trigger mode and with delayed trigger. The traces deflection is always full realtime and that helps a lot.

All it takes is a burst sequence on a serial bus and a newbie could royally screw up the scope plot. That is fairly common.

--
Regards, Joerg

http://www.analogconsultants.com/

OK, you and Phil have convinced me that our newbie is more likely to get in trouble with a DSO than an analog scope.

I guess that just means we now need a bit more effort towards education before handing our newly minted EE his new DSO? ...since it's not like analog scopes are ever coming back in any large number. :-)

Don't count on it, universities won't likely deliver in that domain. We should put our thinking caps on and include simple circuitry and software that can issue a spectral spill-over alert.

Sometimes this is easy. I've introduced this scheme to an ultrasound company and could not believe when it dropped some jaws: Doppler has the same problem, you can get serious aliasing in the FFT if the doc selects the wrong settings. Usually it's visible but sometimes younger docs might store an aliased and thus rather lousy plot. So I suggested to slightly scoot the sample rate and see if that makes anything in the spectrum move in the wrong direction. Seems that medical device folks barely or never peek over the fence to see how the Radar guys do that. Because they use such schemes since almost forever, except they don't call it alias but target ambiguity.

...since it's not like

Coming back? They are here with us, right now, new and fresh:

If you shop around you can get this one for a little more than $1600 plus tax. Even the rental place that I use sometimes has them if you only need it only for a month or so.

--
Regards, Joerg

http://www.analogconsultants.com/

That depends on whether they use variable sample rates or not. AFAIK most scopes use variable sample rates.

--
Failure does not prove something is impossible, failure simply
indicates you are not using the right tools...
nico@nctdevpuntnl (punt=.)
--------------------------------------------------------------

With some care, I could see that on my sampling scope, but the digital wavemeter method was more fun--peak-to-valley in 1/4 inch of hand motion

-> oscillation frequency ~ 12 GHz.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal Consultant
ElectroOptical Innovations LLC
Optics, Electro-optics, Photonics, Analog Electronics

160 North State Road #203
Briarcliff Manor NY 10510
845-480-2058

hobbs at electrooptical dot net
http://electrooptical.net

Sometimes it is good to let the spectrum analyzer run in the background, connected to rabbit ears that are over the work bench. Mine has a limit function and it'll annunciate if something peeks outside the limits. If I was more of a programmer I could write myself a little routine that lets that start a brief audio file. Maybe a fire bell sound ...

--
Regards, Joerg

http://www.analogconsultants.com/

Yes, yes, but that's still "just barely hanging on in small numbers," not "coming back in large numbers." :-)

Given the cost is no more than a couple days of a consultant's time, you could probably get a lot of clients to buy'em after demonstrating the utility...

By default they do at slower sweep speeds; most can be forced to sample more quickly, at the expense of the stored length (in seconds) of the trace, of course. (Sometimes it's only indirectly via, e.g., peak detect modes... some, such as LeCroy, will let you force the sample rate to pretty much whatever you want.)

[...]

Think of it this way: You've just built the worlds's highest frequency theremin :-)

--
Regards, Joerg

http://www.analogconsultants.com/

Or worse, use of that spiffy HEMT with wires..sweep rate might then need to be "as fast as you can get and do not blink"..

Newark wouldn't have five of these in stock if they were slow sellers:

It's too big to schlepp around. The usual scenario is that I suggest to clients to buy a Tek 2465 at auction. When it arrives there are usually oohs and aahs. One engineer said "This is like we just switched to high beam".

--
Regards, Joerg

http://www.analogconsultants.com/

Bizarre. It's an analog scope described as "CRT Colour" and "20 MSPS".

And the price is insane.

The new digital scopes are so cool, I can't imagine ever using an analog scope again.

--

John Larkin, President
Highland Technology, Inc

jlarkin at highlandtechnology dot com
http://www.highlandtechnology.com

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