Electronics > Beginners

Oscilloscope training class (long)

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Grandchuck:
You do not have to spend hundreds of pounds.  Look around and you will find many, many inexpensive offerings.  Also, used scopes can be great buys.

xrunner:

--- Quote from: Grandchuck on December 18, 2023, 01:08:46 pm ---You do not have to spend hundreds of pounds.  Look around and you will find many, many inexpensive offerings.  Also, used scopes can be great buys.

--- End quote ---

 :-+


--- Quote from: lieinking on December 17, 2023, 10:44:26 pm ---Is there anyway around buying an oscilloscope or paying so much?

--- End quote ---

The term "paying so much" is very subjective. What is the budget you are allowing yourself? You can get a used 20 MHz analog scope for under $150.

If "paying so much" means $25 to you, then you will have a hard time getting one.  :-//

radiohomebrewer2000:
Is there a tutorial video out there of someone showing how to do a stable measure of a AC waveform on an oscilloscope?

Really, a radio frequency wave - say about 2 MHz, 5 MHz, or 7 MHz.

I am interested in the numerical frequency and voltage. 

More specifically, I would like to measure a VFO or oscillator of a transceiver like a NorCal 40B CW Transceiver Kit.  There are various test points already on the PCB you can use to test.  However, using my old HP scope or my new Siglent scope, the measurements bounce around.

Here is a topic on EEVBlog already. 
https://www.eevblog.com/forum/rf-microwave/how-to-get-a-stable-measure-of-v-and-freq-using-an-oscilloscope-on-a-vfo/

I was just wondering if someone has a video or tutorial already of this scenario.

My old scope is a HP 54600B 100 MHz 2-channel digital scope from the early 1990s.
My new scope is a Siglent SDS814X HD 100 MHz 4-channel digital scope - this scope has a hardware frequency counter; however, it still requires a few seconds to display a stable measurement for the frequency.

In the link above, there was some good suggestions like using the average to get a stable reading.  Or add more periods.  Or create an inductor that has a few turns.   I do not think just getting the probe near the test point will work.   I have to touch the test point with the probe to get a reading.   If I want a stable frequency reading, I can hook it up to my old HP frequency counter.  But I just rather do it all in my scope.

There are "trigger" options in an oscilloscope, but I am clueless about them.   Besides, the wave form seems to display OK - stable.  It is the numerical readings I am interested in here.

Thanks in advance.

shabaz:
Connecting anything to the output of the VFO will load it slightly, so it's not possible to precisely set it to a frequency using that method. However, you can use the scope to trim any adjustments in your circuit to see when the 'scope shows a signal that isn't weak and collapsing (such circuits will oscillate well in a range, and the output may collapse at extremes).
It probably won't look like an ideal sine-wave, this is OK. If you really want a voltage measurement, then even a peak-to-peak measurement (using cursors or automated measurements, either will be fine, there's no need for accuracy) is sufficient (I've not checked your documentation to see if p-p is what is being asked). If (say) the documentation says to adjust to 500mV p-p, then if it is 450mV or 550mV makes little difference.
If the measurement is very low, it may well collapse and produce unstable results. But there's a very good chance the unstable results are from a triggering issue. A screenshot/capture from your 'scope will help to narrow that down.

Once you're in the ballpark frequency based on what you've measured on the 'scope (automated measurements, but do a sanity check using cursors too, or with calculator and eyeballing it), and once the amplitude is in the ballpark you are expecting, then you could remove the 'scope, and then try to tune in your receiver to a known frequency transmission, and then fine-tune based on what you hear.

The screenshots below show two example 'scope traces for a particular VFO (different to your design, i.e. not related to that attached schematic) set to a center frequency, and to an extreme frequency.

Notice how the right-side screenshot looks more like a sinewave. However, that right-side screenshot actually shows a lower amplitude (see the volts per div setting on the screenshot), and and it is unstable (see the fuzziness on the trace).
The left side screenshot is actually the better setting. There, the amplitude is higher, and the signal is stable. The actual shape of it is less important, because it is normal for there to be harmonics that will cause that misshapeness.



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