How to read frequency on an oscilloscope?

Thread Starter

Tonyr1084

Joined Sep 24, 2015
7,853
Have an old Techtronix scope. Trying to understand the sweep: Sec/Div.

I have it set to 20µ and the sine wave is two major divisions. Is the 20µS per major division or per the minor divisions? If minor - would that be 4000 Hz?

How would I calculate the Hz?

The frequency I'm trying to understand is supposed to be ultrasonic, so 4kHz would be WELL within normal human hearing range. It's GOT to be greater than 20kHz. A dog barking device that's supposed to distract the dog and stop them from barking. I want to know what frequency it's operating on.
 

LesJones

Joined Jan 8, 2017
4,174
I am assuming that you mean that it is set to 20 uS per major division. (That is the normal way the calibration is marked.) So as the sine wave is two major divisons that is 40 uS. One second is 1000000 uS so 1000000/40 = 25000 Hz (Or 25 KHz)

Les.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
7,853
Thanks. Makes sense to me now. Expected something greater than 20kHz. Dog hearing range.

I am assuming that you mean that it is set to 20 uS per major division.
There's no other markings on the dial other than 20µ and Sec/Div. That's partly why I'm wondering if it's major or minor divisions. The minor divisions are 5 to one major division. (four small marks between the big marks)
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
7,853
It's a T921. Single trace. Been kicked around a bit before I got ahold of it. Knobs need some cleaning and probably a new solder joint or two. Sometimes the sweep doesn't behave properly. Also not very confident in its calibration.

For dual trace I have a PC based Hantek. Does the job but I'd have to hook up the computer and I don't feel like doing that. I'm on a Mac right now and the Hantek operates on Windows. The Tektronix is just a plug away from being switched on. And the Hantek does the math for me. Keeps me dumb.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
7,853
Also have a Tektronix 561A. Four trace (3S74) but the darn thing wanders constantly. It needs serious help. I'd sell it if I could find a buyer for it. I also have a couple other plug in modules I know nothing about other than they slip in and out of the chassis. A 3S76 and a 3T77A. They have the old connectors (before BNC connectors). I think I even have a connector or two for it around somewhere along with two 10X Attenuators.

There is a test lead as well (BNC connector type).
 

dl324

Joined Mar 30, 2015
16,846
Those were the first Tek scopes I used at school. We coveted the newer ones, but the older ones were more available.

You probably have some weak tubes.
 

Thread Starter

Tonyr1084

Joined Sep 24, 2015
7,853
Some weak tubes ? ? ? Yeah, getting older for sure. Pushing 70 these days it feels like. (not 70 - just feeling that way after a heavy wet snowfall)

It's dinner time boys and girls. Will check back a little later.
 

sv3ora

Joined Jul 29, 2023
1
Also have a Tektronix 561A. Four trace (3S74) but the darn thing wanders constantly. It needs serious help. I'd sell it if I could find a buyer for it. I also have a couple other plug in modules I know nothing about other than they slip in and out of the chassis. A 3S76 and a 3T77A. They have the old connectors (before BNC connectors). I think I even have a connector or two for it around somewhere along with two 10X Attenuators.

There is a test lead as well (BNC connector type).
Dear Tonyr1084,
I want to buy these 3S76 and 3T77A plugins from you, if you still have them.
I am also interested in a 3L10 plugin.
How can I reach you please?

My contact information is here <snipped> at the end of the page.
Thank you very much!
Kostas

MOD EDIT: Link snipped. If @Tonyr1084 is interested, he can PM you and you can make arrangements.
 
Last edited by a moderator:

Thread Starter

Tonyr1084

Joined Sep 24, 2015
7,853
Sorry, that scope was sold years ago. Since my last post on this thread was back in 2017, that's six years gone by.

If there are any to be had, I'm sure someone here will be able to tell you where you can find them.
 

tautech

Joined Oct 8, 2019
383
This subject is the very thing that drove me nuts with CRO's and led me to DSO's with which frequency display and simply grabbing screenshots to USB are valuable capabilities.
Nice round # frequencies are easy with a CRO but how often do we strike those ?
 

KL7AJ72

Joined Apr 15, 2021
22
Have an old Techtronix scope. Trying to understand the sweep: Sec/Div.

I have it set to 20µ and the sine wave is two major divisions. Is the 20µS per major division or per the minor divisions? If minor - would that be 4000 Hz?

How would I calculate the Hz?

The frequency I'm trying to understand is supposed to be ultrasonic, so 4kHz would be WELL within normal human hearing range. It's GOT to be greater than 20kHz. A dog barking device that's supposed to distract the dog and stop them from barking. I want to know what frequency it's operating on.
Also, when using a scope to measure frequency, ALWAYS use the zero crossing as the reference point. Lots of "noobies" use the peak of the waves....very inaccurate.
 
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