hi, I am new to a lot of this and wondering if I can figure out 50% modulation with analog scope? Scope is at 5 volts/div in picture.

Setup with scope says to set the 'level' at mid position I guess that isi 50%?

I cal at 20v pp for most settings (manual) & at mid level little less than 10v pp. so close to 2.5v with 50% deviation or half of 10v? thanks trying to understand.

instructions

How to calculate modulation percentage:

http://rfcec.com/RFCEC/Section-3%20-%20 ... le%20K4RFE).pdf

get error on link? maybe shorter link - simplify http://rfcec.com? thks

Sorry it wasn't a good link. But the info is widely available.

"http://rfcec.com/RFCEC/Section-3%20-%20Fundamentals%20of%20RF%20Communication-Electronics/33%20-%20TRANSCEIVER/Transceiver%20-%20Amplitude%20Modulation%20Percent%20of%20Modulation%20(By%20Larry%20E.%20Gugle%20K4RFE).pdf"

Eliminate the quotes. The system truncates the link if I don't add them.

thks will try and pull out only the key words and try

No, just highlight the link but only the part inside the quote marks and you will have it.

you got me and Da........... between bad eyes and clicking the link I got error removed the quotes and it work, thanks for the kick. I wont say I built websites & have cis degree along with admin work. thks...

I think I am about where I can be w/o a reference. Need to get a dig scope to help verify my thinking someday..

There are some tricks to getting a good stable trigger on a modulated RF signal. You won't be able to determine the modulation level very easily until you can get good stable triggering.

One approach is to adjust the trigger level to near the peak of the modulation, in other words, way above zero, until the trigger level is so high that the scope doesn't trigger any more, then back off a little.

Another approach is to rely on some of the modulation coming through at audio frequencies (i.e. feedthrough from the modulation signal), and so set the trigger to "HF Reject" and hope there's enough audio coming through to trigger on. Your scope doesn't give you this option.

A third and very good approach is to apply the AF modulation signal (not the modulated RF, just the signal that's modulating the RF) to the external trigger input and set the trigger to EXT.

A different approach is to skip trying to get a stable trigger of the modulated RF, and instead set up the scope for a trapezoidal waveform. You can read about it in just about any edition of the ARRL Handbook. Here's a couple of web links, too:
https://www.tpub.com/neets/book21/90a.htm
http://rfcafe.com/references/radio-news ... o-news.htm

By the way, what was your scope triggering on? In the photo, it looks like the trigger selector was set to EXT rather than CH1.

thks.. I was/am trying to cal my eci transistorized 80s function generator. wanting to understand how to cal 50% mod on the scope if possible at those settings. Dont have much RF experience. Math is what I could work with.. might not be that simple.

Someday if I get a dig scope I might not further learn to read a scope. need both.

2v/div, dc in pict. sine wave not very rounded

p.s. set up as previous described..

Slow down the sweep to something closer to the period of the audio modulation. It’s hard to tell, but I think the photos are showing a few cycles of the RF carrier, with a low level of modulation, only about 30%. That might just be an artifact of the triggering, though. Slow the sweep down until we can see a few cycles of the audio modulation. That’s where the triggering gets tricky, you might need to hook up the external trigger or go to X-Y mode and look at the trapezoid.

will this work? 2vdiv - mid level gen set
how do you fig out 50% mod? is it just linear math? thks

Do you have a manual for your scope? In the photo, you have both X and Y inputs set to be CH1.

Does your function generator have a separate output of the modulating signal? If it doesn’t, you can’t easily make a trapezoidal display of the signal.

If it does, then set the Y Mode, on the left-hand side, to CH2. Then disconnect the main function generator output from VH1 and instead connect it to CH2, so it will be the Y axis signal. Then connect the modulating signal output of the function generator to the CH1 input of the scope. Adjust the VOLTS/DIV knobs until the whole trapezoid fits within the scope screen.

As for calculating the percentage of modulation, did you read either of the links I previously posted? I can’t explain it any better than the links do. The RFcafe link has a picture that summarizes the calculation:


Read the links and then come back with specific questions if there is something you don’t understand.

manual shows only half pages,,, again.. this is a good link

bad link https://www.ece.rice.edu/~jdw/data_sheets/ss5702.pdf

good link for me anyway - https://elektrotanya.com/iwatsu_ss-5702 ... nload.html

my scope needs two inputs for x-y no? when I use my octopus box I use two feeds?

is this what you are asking? took this pict yesterday before the x-y picts above.. slowed the sweep down, believe its in 2vdiv.. thks

Well, your scope photos show an XY display with only one signal, so no, your scope can do XY with only one input. That’s not very useful, though, because it will always just show a 45 degree line.

But yes, in general you want two different inputs for XY mode.

Yes, that’s what I meant when I asked you to slow down the sweep.

The drawing I posted tells you exactly how to calculate the percentage modulation from that scope display.