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- Опубликовано: 4 мар 2024
- This is a followup from video #382 where I demonstrate how to measure Am modulation depth using a digital oscilloscope. In this video, we take a look at how to perform the measurement with an older analog scope (Tektronix 485). Additionally, the measurements will be performed on low-cost RF signal generators. Here is a link to the previous video:
• #382: Measuring AM mod... 
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Thank god there is someone like Alan to share and explain all this knowledge. You Sir are a nugget of gold🤓🙂
It's always a joy to see the 485 doing something useful! :-)
Thanks, Alan! Really nice to see a use for the uncalibrated vernier controls. I love these analog scopes!
Bingo! Outstanding explanation and visual showing of this measurement via capabilities of an analog scope! Thank you very much!
Thank you for showing how to measure the modulation index on an analog scope.
Another student checking in to the ocilloscope school, Thanks Alan.
It really is amazing what the TinySA can do. I can't wait to see what else they can cram into those things 5 years from now!
Enjoyed your video!! Gary Grove Minneapolis, MN
A month ago I was kinda struggling with this concept. I was trying to figure out where was the "modulation depth" figure from a signal generator coming from, because my naive assumption was that it was probably a % of VP, but that wasn't matching any measurements I was able to make. After watching this video (and the previous one) I had to try both on analog and digital scopes, and it made everything so much clearer to me. Now I totally understand how it's calculated and can check/calculate this parameter myself.
Thanks!
Thank you sir, always be healthy
Awesome! Thanks for sharing this. Really cool looking output of the TinySA . Your scope knowledge is unparalleled. Take care and 73.
Sweet! Digital is makes life easy, but analog make you understand what is going on!
Very intuitive. Great video...and I love old equipment earning its keep.
Thanks for showing the analog version. I was about to ask for one on the other video as well.
You just can't beat an analog scope for RF envelopes. You can't quite get rid of the triggering jitter on digital scopes easily. The 485 was rock solid with little effort and what a gorgeous display. I'd never give up my Tek 7844R dual beam scope on my bench. I also have a couple of Heathkit SM5228 VTVM's hanging off my equipment shelves that I use for things like aligning radios, you just can't beat a swinging needle for fast peak/null settings of analog signals that I wouldn't ditch either.
I use an analog scope for my RF time domain measurements. Tektronix 2235. Not super high bandwidth but good enough for HF work.
If you have TinySA with AM modulated signal you get carrier frequency and two side bands. The amplitude of side band compare to the amplitude carrier is related to your modulation index:
m=10^((x+6.02)/20)
m=modulation index
x=the difference between carrier amplitude and side tones in dBV
for details please do a search "Measuring the Modulation Index of an AM Signal using an FFT"
Love your work man. Keep making them.
there is a 100% scale on the old tek, too (y) tnx for new input, Alan. And congrats to 200k subs. 73
The 100% scale is used mainly for 10-90% rise and fall time measurements. The 100% scale is shy of the graticule's full scale to account for overshoot/undershoot on the edges.
Awesome & thanks for the video!
Watching the last one, I felt sure that you couldn't do the measurement with an analog scope... great video!
What purpose would a analog oscilloscope serve if it couldn't take measurements? That's why it has calibrated time base and voltage settings for the scale.
@@mikesradiorepair Actually, early oscilloscopes didn't all have calibrated time base and voltage settings. The ability to "see" a waveform was big advantage of the scope. In fact, for the purpose shown here, he is not using the calibrated scales. Many years ago a friend gave me an ancient Heathkit scope which did not have a calibrated display.
👍Thank you sir.
I have a Tiny SA and some DSOs, but also an HP 1740A 'CRO' and a B+K sig gen very similar to yours. So it was good to see the comparison. Sometimes analog is good, and I do miss all those 'scope knobs. 73
These all Teks are such high quality equipment. They seem to last forever, and the pleasure of using their buttons seems unparalleled. They still sell for a good price. The only problem is the room they take.
Nice! And now FM modulation depth please!
I do have a few videos on measuring FM modulation index:
Bessel Null method: ruclips.net/video/8IBOYoIV5m8/видео.htmlsi=b3609rda__8E5QUr
Spectrum Analyzer method: ruclips.net/video/Nw3_w1HrlEs/видео.htmlsi=oB8UkNpGjTKMgazs
Unfortunately, there isn't a really good/accurate way to do this in the time domain with a scope because the change in frequency (deviation) is typically much, much smaller than the carrier frequency, so the difference is hard to measure. One more complicated option would be to down-convert to a lower frequency so that the deviation is a much larger fraction of the carrier (the principle behind the pulse counting FM detector: ruclips.net/video/jQlN2fc7LJc/видео.htmlsi=-LIZgbyeifYtIBv9).
@@w2aew Thank you very much! Will look into it.
Thanks Alan, is it save to say that the HP 15c named Wolke is from your University time? Nice calculator. Have the 28c and once you get used to RpN you never want to go back
No, but shortly after. Purchased in the late 80s I think.
Nice 485!
A 485 found its way into my vintage Tek collection about a year ago. Unfortunately, it has a triggering issue that is probably due to bad tunnel diodes. I haven't had time to work on it any further yet.
Great scope! I hope you can fix it. The 485 has a very sharp trace on its CRT.
@@w2aew
Even wilder, my 485 has a P11 phosphor CRT. It's the only scope in my collection with a P11 phosphor.
Hey there, i just got an oscilloscope Tektronix 465b, in perfectly condition and for free at that. Newer to electronics and wondering which of your videos youd say are best for learning oscilloscopes and all that. Thanks!!
I have a playlist for oscilloscope basics, many of which feature the 465 B
I am considering building the direct conversion transceiver in Eamon Skelton's book; "Build a Transceiver". I've been reading about RF leakage in these transceivers. My question is; is this a serious problem or an annoyance? Is there a solution? Should I consider building a heterodyne unit instead?
Sorry, not familiar with the book or the design of the direct conversion circuits in this book.
What's with the using of conductive pointers, diodegonewild is even worse he used scissors in his last video.
Seemed like a fun use for a broken probe.
why not just say 'part 2'
Well, I wasn't planning to do a part 2 (so no mention of it in the first video), so I just called it a follow up.
@@w2aewI see, thanks