RLC bridge

My clients usually want to know right now what's wrong. Infinite persistence does not help because the noise does not always show up in the same place.

I have done several sessions like that with a Pilsener or two in my belly :-)

I have to confess that I use DSOs more than the analog ones and my old low-BW analog scope is even in the storage closet.

I always loved "panoramic adaptors" which are essentially poor man's spectrum analyzers that hook up in front of the IF strip of a radio. Only rich ham radio guys had those and I built mine around an analog scope.

Tell them to consider it a loaner scope from da boss :-)

sellers.

Tell that to Joerg.

Wait until you have your first case of noise of unknown origin :-)

My Tek 7704 doesn't get a lot of use either these days but if it does it's usually cases where a DSO simply can't see stuff. Often the 7704 shows me what's there, I get a grasp of the spectral composition of the noise, and only then can I train my DSO on it. Mostly to be able to put that in the client report because snapping a photo off of the 7704 is more hassle.

My main reason for preferring the DSO is ecological. Pulling the magic button on the 7704 results in a *TUNGGG* sound and you can almost hear the amps flowing. These things were designed when nobody gave a hoot about amps and watts and energy in general. The engineers back then cruised around in cars like the Plymouth Fury. The DSO only sips power, you can run it all day long and the lab temperature won't rise a bit.

It certainly is that seldom for me. I can't remember the last time I actually needed an analog scope. It was likely long enough ago that I didn't even

Come on! Test equipment isn't necessary for government to waste money.

sellers.

That probably has to do with the fact that our lines of work are very different. I do a lot of very noise-sensitive pulse-echo stuff. Until DSOs have an instantaneous dynamic range of more than 80dB plus trace repetition rates of several million per second they won't be very useful for a lot of my measurements. A lot of water will flow down the Mississippi until that happens.

True. In California they currently prefer the "High-Speed Train to Nowhere" for that purpose.

I bought it only about a year ago, so I don't need convincing. I also have a Tek 475 right next to my bench.

You're going all European on us. ;) Compared to turning down the heat by a degree or two, a scope is a drop in the bucket.

Cheers

Phil Hobbs

We get several calls/emails a year with some complaint/ question that's due to alaising. (' course these are (fellow) physicists.) Digital sources into DSO's seem to make it easy.

Thanks for the peak detect trick, Nico.

Our standard answer is to ask them to think, "What's the frequency of interest and 'your' time base"?

Suggesting 'pushing the right buttons' may save a few calls.

George H.

Would a linear to logarithmic pre-amplifier help to get more dynamic range on a scope? I guess it will take some time to get used to look at signals like that.

actually

It would *show* more dynamic range but that's why we have the vertical gain knob. ;-) OTOH, it doesn't help the noise floor a bit so you haven't gained anything. Better bandwidth selection might help some.

Interesting... What kind of rabbit ears do you use to probe your bench space?

Don't you mean "analog scope"?

Mine is on a cart, too. Lots of storage for extra plugins.

Yes, I meany analog.

The same ones we used to watch Bonanza and Lassie before I was in school. Nearly all the gold color has flaked off after about half a century, it's rather ugly by now, but works. It looks like a big bowtie without reflector. The good thing is it has a heavy steel foot so it won't tip over and a gooseneck that allows me to adjust where it points.

In fact, I used that thing at a client to find EMC issues. Hovering over all the parts of the installation I could pinpoint hotspots, then chase stuff with the near field set (I use the EMCO kit). Then they passed class B.

You have an invitation to visit us in August and spend a couple hours in my lab, that might change your mind :-)

Hint: The A/C is typically not running ...

actually

Not really. Sometimes I have to detect a faint pulsating "thickening" of the trace somewhere and a logamp would easily make that go under. 8-bits is simply useless for stuff like that. To add insult to injury, that noise is generally totally asynchronous, meaning the thickening wanders or whizzes through. So any kind of averaging on a DSO is hopeless.

Think of it this way: The (analog) eye of a well trained driver can detect a faint glistening 100ft or more to the side of the road in the brush, a few hundred feet ahead, and cause the driver to set the foot onto the brake. Sure enough, five seconds later a big deer jumps into the road. BT. The glistening was the eyes of the deer. That is totally impossible for an automated system based on digitized image input.

I'd love to come--you think NoCal is bad in August, I invite you to New York.

Cheers

Phil Hobbs

But most people up there run the A/C all day long. Here in the office/lab it can easily be 90F or more. Those are not my favorite days to start a major SPICE simulation session or used too many of the boat anchors. Sometimes it can't be avoided and then I start very early in the morning.

Alabama.

Hmmm. I graduated from HS there (west side), Lynbrook. What years, = level and school?