Video showing undermodulation and overmodulation

Summary

In this video, the creator expresses gratitude to long-term subscribers and discusses the limitations of his equipment. He then delves into a demonstration of amplitude modulation, explaining the concepts of under modulation and over modulation using an oscilloscope. The creator clarifies the importance of modulation percentage in transmitting information and shows the effects of different modulation levels on the signal quality. He also shares his preference for analog oscilloscopes over digital ones and briefly reviews a cheap digital model.

Takeaways

• 🙏 The video creator expresses gratitude to long-term subscribers for their continued support despite the limitations in production quality.
• 🛠 The creator acknowledges having a limited workspace and basic equipment, such as a cheap camera, but makes the best use of what they have.
• 📺 The creator watches videos from their subscribers and gets recommended content on YouTube, which sometimes diverts them from their intended viewing.
• 📡 The video revisits the topic of modulation, specifically addressing the concepts of under modulation and over modulation, which were not clearly explained in a previous video.
• 🔍 The creator is not a modulation expert but shares practical knowledge gained from their work, aiming to clarify what modulation percentages mean in practice.
• 📶 The video demonstrates how different modulation percentages affect the AM waveform, showing the carrier and modulating signals on an oscilloscope.
• 🚫 At low modulation percentages, the audio information can be lost, which is why very low modulation levels are not used.
• 🚨 Over modulation leads to gaps in the waveform, which can cause signal clipping and distortion, hence the importance of avoiding it.
• 🔧 A primitive demodulator is built to remove the carrier and show the effects of over modulation on the audio signal.
• 🔄 The creator compares analog and digital oscilloscopes, expressing a preference for analog scopes but acknowledging the adequacy of digital ones for basic tasks.

Q & A

What is the main focus of the video?

The main focus of the video is to demonstrate and explain the concepts of under modulation and over modulation in the context of amplitude modulation (AM).

Why does the presenter express gratitude to their subscribers at the beginning of the video?

The presenter expresses gratitude to their long-term subscribers for continuing to watch their videos despite the limitations in production quality and resources.

What limitations does the presenter acknowledge in their video production setup?

The presenter acknowledges having a limited size workbench, no access to various cameras or microphones, and using a cheap camera for their videos.

What was the topic of the previous video mentioned in the script?

The topic of the previous video was modulation percentage, specifically discussing AM alignment and the setting of modulation levels.

Why is it important to avoid very low modulation percentages?

Very low modulation percentages can cause the valleys and peaks of the waveform to disappear, resulting in the loss of information, making it inaudible or ineffective for transmission.

What happens when modulation is set to 100% or more?

At 100% modulation or more, gaps appear in the waveform, which can lead to parts of the signal being clipped and lost, causing distortion and signal loss.

What is the purpose of a demodulator as shown in the video?

A demodulator is used to remove the carrier signal from the modulated wave, leaving only the audio information, which can then be amplified and played through a speaker.

How does the presenter demonstrate the effects of modulation?

The presenter uses an oscilloscope to visually demonstrate the waveforms at different modulation levels, showing the effects of under modulation and over modulation.

What is the presenter's stance on digital versus analog oscilloscopes?

The presenter prefers analog oscilloscopes for their work but acknowledges that a cheap digital oscilloscope can be suitable for basic electronics work.

Why might someone choose an analog oscilloscope over a digital one?

An analog oscilloscope might be preferred for its familiarity, ease of use, and real-time display of waveforms without the potential lag or latency that can be present in digital scopes.

What advice does the presenter give regarding the purchase of a digital oscilloscope?

The presenter suggests that the decision to purchase a digital oscilloscope should be based on personal preference and budget, and that the cheapest models may have limitations.

Outlines

00:00

📺 Understanding AM Modulation

The speaker begins by expressing gratitude to long-term subscribers and acknowledges the limitations of his equipment. He discusses a previous video on modulation percentage and the feedback received about not showing under and over modulation. To address this, he demonstrates the appearance of these modulation states on an oscilloscope. He clarifies that he is not an expert but explains the basics of AM modulation, which consists of a carrier wave and a modulating audio frequency. He shows how different modulation percentages affect the waveform, highlighting the importance of not setting the modulation too low, which would cause loss of information, or too high, which would lead to distortion and gaps in the waveform. The speaker also mentions building a primitive demodulator to remove the carrier and leave the audio signal.

05:03

🔍 Demonstrating Modulation Effects

In this segment, the speaker uses a homemade demodulator on a breadboard to visually demonstrate the effects of over modulation on a sine wave using an oscilloscope. He points out the distortion and gaps that occur, explaining why over modulation is undesirable. The speaker then contrasts the use of a cheap digital oscilloscope with his preferred analog oscilloscope, discussing the differences and his personal preference. He shares his experience with the digital oscilloscope and mentions that while it's the cheapest option, he finds the analog scope more suitable for his work. The speaker concludes by reiterating his preference for the analog oscilloscope and thanks the viewers for watching.

Keywords

💡Modulation

Modulation is the process of varying one or more properties of a periodic waveform, called the carrier signal, with a modulating signal that typically contains information to be transmitted. In the video, the creator discusses modulation in the context of AM (Amplitude Modulation), where the amplitude of the carrier wave is varied in proportion to the message signal. The video aims to show the effects of under-modulation and over-modulation on the carrier signal, which is crucial for understanding how information is transmitted in AM radio.

💡Under Modulation

Under modulation refers to a situation where the modulation index is set too low, resulting in a signal that does not fully convey the information of the message signal. In the video, the creator demonstrates under modulation by showing how the valleys and peaks of the AM waveform disappear at low modulation percentages, leading to a loss of information. This is critical because it affects the quality of the signal received, potentially making it inaudible or distorted.

💡Over Modulation

Over modulation occurs when the modulation index exceeds 100%, causing distortion in the signal. The video illustrates over modulation by showing gaps in the waveform, which would lead to parts of the signal being clipped or lost. This is undesirable as it results in a signal that is not an accurate representation of the original message, leading to poor reception quality.

💡Service Manual

A service manual is a technical guide that provides instructions, specifications, and procedures for the installation, maintenance, and repair of equipment. In the context of the video, the creator mentions service manuals in relation to setting specific modulation levels, such as 30% modulation, for AM alignment. This highlights the practical application of modulation concepts in the real-world maintenance and setup of electronic devices.

💡Audio Frequency

Audio frequency refers to the range of frequencies that the human ear can hear, typically from 20 Hz to 20 kHz. In the video, the creator discusses how the audio frequency, which carries the information or 'intelligence' of the signal, rides on the carrier wave in AM modulation. The modulation process is essential for transmitting these audio frequencies over a distance.

💡Oscilloscope

An oscilloscope is an electronic test instrument that allows the observation of varying signal voltages, typically as a two-dimensional plot of one or more signals as a function of time. The video creator uses an oscilloscope to visually demonstrate the effects of modulation on the waveform. The oscilloscope is a key tool in electronics for diagnosing and understanding signal behavior.

💡Demodulator

A demodulator is a device or circuit that extracts the original information-bearing signal from a modulated carrier wave. In the video, the creator builds a primitive demodulator to remove the carrier and leave only the audio signal, demonstrating what happens to the signal when it is over-modulated. This process is essential for receiving and decoding radio transmissions.

💡Carrier Wave

The carrier wave is a waveform, usually sinusoidal, that is used to transmit information in various communication systems. In the video, the carrier wave is mentioned as the 500 kHz signal that is modulated by the audio frequency. The carrier's properties are altered to encode the message, which is then transmitted and later demodulated to retrieve the original information.

💡Modulation Percentage

Modulation percentage refers to the degree to which the carrier wave is modulated by the message signal. In the video, the creator discusses the implications of different modulation percentages, such as 10%, 30%, or 100%, and how they affect the quality and integrity of the transmitted signal. Understanding modulation percentage is crucial for optimizing signal transmission.

💡Information Loss

Information loss occurs when the transmitted signal is not accurately received due to various factors, such as under or over modulation. In the video, the creator shows how under modulation can lead to a loss of the signal's peaks and valleys, resulting in a quieter or inaudible signal. This concept is important for understanding the limitations and challenges in signal transmission.

💡Digital Oscilloscope

A digital oscilloscope is a type of oscilloscope that samples and digitizes the input signal, providing a display of the signal waveform on a screen. The video creator compares a digital oscilloscope to an analog one, discussing personal preference and the suitability for electronics work. The digital oscilloscope is shown as a more affordable option, but the creator prefers the analog scope for its familiarity and reliability in their work.

Highlights

The video begins with the creator expressing gratitude to long-term subscribers and acknowledging the limitations of their equipment.

The creator discusses their viewing habits, including watching subscriber videos and being recommended unrelated content by YouTube.

A previous video on modulation percentage is referenced, with a focus on the lack of demonstration on under and over modulation.

The concept of modulation is introduced, explaining the difference between under and over modulation and its impact on signal quality.

The video demonstrates how to adjust modulation levels using an oscilloscope to visually represent the signal.

The importance of modulation level in AM alignment is highlighted, with a practical example of setting the output generator.

The creator explains the组成 of an AM waveform, including the carrier and the modulating audio frequency.

A demonstration of under modulation is shown, where too low a modulation percentage results in loss of signal information.

The consequences of over modulation are discussed, leading to gaps in the waveform and signal distortion.

A primitive demodulator is introduced to remove the carrier and isolate the audio signal.

The impact of over modulation on the audio signal is visualized, showing distortion in the sine wave.

The creator shares their preference for analog oscilloscopes over digital ones, despite having access to both.

A comparison between the analog and digital oscilloscopes is made, with a demonstration of the same waveform on each.

The video concludes with the creator answering a viewer's question about the suitability of a cheap digital oscilloscope for electronics work.

The creator emphasizes the importance of modulation levels in maintaining signal integrity and the practical demonstration of these concepts.

Transcripts

so I'm back with another short and

hopefully interesting video but first I

just want to say thanks to all my

long-term subscribers that still watch

my videos on a regular basis I know

they're not perfect but I do try to do

the best that I can do I do have limited

means here I have a limited size

workbench and all that I know I don't

have various different cameras or

microphones I have a cheap camera but it

works also I do watch the videos of my

subscribers I don't watch very many

other videos say other electronics

channels lessor subscribers of mine even

if I didn't want to do that

YouTube always recommends videos to me

like hyenas attack Lions in the

Serengeti or something like that then I

end up watching that instead so back to

my original subject here not too long

ago I did a video on I think it was

modulation percentage or it could have

been a little while ago and one

commenter noted I didn't really show

under modulation and over modulation so

I'm just gonna go ahead and show that

real quick on the scope how that would

look I am by no means a modulation

expert or anything like that this is

really an area that really doesn't

interest me that much if for example you

have a service manual and you want to do

say AM alignment and it says for example

set the the output generator for 30%

modulation or something like that well

what exactly does that mean and for

example why not use 10% modulation or

why not use 100 percent or even more

than that right so I'm just gonna go

ahead and show how the waveforms look

real quick and maybe you can see then

why you shouldn't for example use 20

percent modulation or

you shouldn't run up run it up to 100 or

more percent anyways i made of course

another masterpiece here as far as am am

waveforms are concerned basically to

consist of two parts the carrier and the

audio frequency the audio frequency if

you will basically get rides would you

say it rides on the carrier this is the

intelligence this is the information the

audio frequency audio frequencies

basically it could be music a sine wave

or anything like that and when you put

that together that kind of looks like

this on the scope it's not pretty but

hopefully you can get the general idea

okay off to my next step so here is the

amplitude modulated waveform the carrier

right now is 500 kilohertz and the

modulating waveform is 1000 hertz

and i'm going to go ahead and take this

down to let's say 10 or 20 percent

modulation and we can watch here if we

watch you the valleys and peaks that's

going to go ahead and disappear that

means for example if you're feeding in a

signal somewhere and you say you have a

loud speaker or something hook up to a

unit you're not going to hear anything

below a certain percentage if you turn

that modulation down to low you're gonna

lose your info right there see that so

that sound that for example this is a

sine wave if that's going to be gone or

if it would be music or something that

would be gone too and you wouldn't get

anything out that's why you can't have

like really low percentages of

modulation now going to the other

extreme i think i can go right up to 100

percent what happens is you get these

gaps here in between the waveforms and

the more you over modulate but wider

these gaps get and that means basically

you're going to be missing parts

basically what's going to have

is say if this was if the generator and

I was hooked up to say a stereo receiver

what we would be getting then part of

the waveform would be clipped that's why

we don't over want to over modulation we

don't want any over modulation again

like I said I'm not a modulation expert

this is just what I picked up along

basically my line of work so I'm gonna

go ahead I made a primitive demodulator

and I'll go ahead demodulator of course

that removes the carrier and that just

basically gonna leave us with the audio

and you can basically see what happens

when I over modulate how that sine wave

is going to look so hopefully what I

built here on a little breadboard is

going to work halfway okay so I have the

oscilloscope probe hooked up to the

little well the detector diode I guess

and so now we can go ahead and take a

look at the scope now we're taking a

look at the scope here and I'm sorry for

the shaking this is shaky cam I'm

holding this with my arm I'm sitting

down below so I'm gonna make this quick

now this is basically under modulation

here

not enough modulation notice what

happens to our information here if the

if we could hear the sine wave coming

out of the speaker that speaker would

get quieter and quieter because

basically we're losing the information D

intelligence now going into opposite way

we watch the sine wave and we can look

here see for example on the bottom here

we've got distortion that's why we don't

want to over modulate anything hope that

kind of makes sense you can see her

again what happens that's why we don't

want that I had shown that just a minute

ago with the modulated waveform we were

getting like a gap in between the

different waveforms that is that gap

that you're I guess seeing right there

one more thing I also have a cheap

digital oscilloscope which I basically

have just used one single time this is

the second time now I just played around

with it for a couple minutes so I have

to kind of like learn the thing because

it is a little bit different than the

analog oscilloscope gentleman had asked

me well is this a good scope to buy

personally I prefer a analog scope he

wanted to know if this would be suitable

I guess for doing electronics work well

it is a cheap oscilloscope so basically

get what your money buys for me this is

good enough but I think the analog scope

will be my main scope to work with this

is the same waveform that we just saw a

minute ago or so now for contrast I'll

go ahead and show the analog scope again

now here's the analog scope here and

this is what I actually prefer to use

and I actually use most of time I got

the second scope because I might like

redo this oscilloscope and it might be

down for a while and I need something in

the meanwhile again as I said it's a

matter of preference but I just prefer

this and that oscilloscope the digital

one that you just saw that's about the

cheapest one you could buy I think

there's some YouTube videos out on that

I haven't really looked at him it didn't

really influence my decision anyways

this is nothing to do with the subject

earlier this is just because some

gentleman had asked me that question

thanks for watching