Single Sideband (SSB): How does it do that? (036)

Single Sideband (SSB) is the standard mode of voice communication for HF operation in Amateur Radio across the globe.
It was used for Intercontinental Telephone communication long before it found its way into Amateur Radio (1923).
In this video I will help you understand the How and Why of Single Sideband communication both on the Transmit side and the Receive side.
I start with its foundation in the world of Amplitude Modulated Phone and how it evolved into modern Single Sideband.

When you look at the spectral content of the AM and the DSB Suppressed Carrier signals, you will notice that there are multiple sideband pips at 1xModulating Frequency, Fm, 2xFm, 3xFm, etc. away from the carrier.
It turns out that the pips at 2xFm and above are due to distortion of the audio, not the "ideal" signal. I discovered this through the mathematical investigation into the "ideal" AM signal which only contains the carrier, Fc, and one sideband pip at Fm away from the carrier on either side of the Fc, carrier.
Furthermore, the real world mixer is not necessarily linear. This fact also adds to the additional sideband pips (and the F1 +/- (F2*n) reality).
If you are interested in playing with this, I've provided the link to my GNU Octave file, below.

I have provided a link to a very interesting video on the history of Single Sideband in the promised links, below. It is 47 minutes long, but contains a lot of cool information. The presenter is Ed Gable (no relation of mine).

Promised Links:
AM, LSB and USB Spectral Content Compared (IC-7610 experiment) Spreadsheet

GNU Octave Simulation & Frequency Content of an Ideal AM Signal

The History of Single Sideband (Antique Wireless Museum)

Time Markers for Your Convenience
----------------------------
00:05 Introductory Comments
01:10 Amplitude Modulation, S.S.B.'s foundation
01:29 Definition of Terms
01:38 Modulation
02:03 Carrier
02:49 What is Amplitude Modulation?
02:57 Amplitude
03:25 A.M. Demo-Introduction
03:59 Time Domain
04:37 Frequency Domain
05:48 Double Sideband, Suppressed Carrier: Introduction
06:56 Generating the Signal
09:27 DEMO: The Tour of the Hardware
10:14 Time Domain
10:50 Frequency Domain
11:44 Single Sideband: Introduction
12:19 A Little Amazing History
13:07 How do we generate the signal?
14:28 Receiving SSB: Introduction
15:07 How do we do that?
15:10 Carrier Injection
15:58 The Product Detector
17:07 Final Comments and Toodle-Oots
-----------------------------

[paullittler]

Just getting into amateur radio and after much searching i finally find a video that describes in detail how SSB works.thank you.

[aaronlindemann]

This video gets an A+ for clear education. This has been the most helpful explanation of SSB signal vs AM. Thank you.

[matthewwilson]

Thank you. I am a teacher just beginning to explore radio for various student projects and this was the first video I came across that showed how the process of carrier removal and side band halving worked to be turned into the original signal that I could readily follow and see the changes to the waveforms. Well done and thank you again for the clear explanation.

[bloguetronica]

The quality of your channel is rare. Very well produced videos. Subscribed!

[BrightBlueJim]

Thank you for presenting a rational explanation of single-sideband signals that does not require an understanding of calculus.

The signals produced by a balanced mixer aren't quite what you describe. They are in fact, F1, F2, F1+F2, and F1-F2, for carrier and modulation frequencies of F1 and F2, respectively. There are no F1+F2*2, F1+F2*3, and so on. The reason you see those frequencies on the spectrum analyzer is due to two things: harmonic distortion in the modulating signal, and nonlinearities in the modulator and stages of RF amplification after the modulator. In your first example at 4:51, you can see that the F2*2 (and its opposite sideband) components are 20 dB below the F2 signal. This is what you should expect to see if your signal generator has just 1% harmonic distortion. But as I said, nonlinearities in the RF path will also cause these sideband components to increase. You mentioned later (11:04) that you were surprised to see odd harmonics but not even harmonics of the modulating frequency in your SSB signal. This is related to they type of distortion in your modulating signal, or the type of nonlinearity in your RF path. Since I assume you're using the same 1 kHz source for both examples, my guess is that the additional signals are being produced mainly by RF nonlinearity. A clue to this is that what you are seeing are only odd harmonics. As you probably know, square waves contain only odd harmonics. So any kind of nonlinearity that behaves like a square wave is likely to show domination by odd harmonics. In practice, "acting like square waves" is what happens when both peaks of your RF signal are being clipped or limited. It is this symmetrical limiting that is the most common nonlinearity in RF amplifiers, and also the reason you see mostly odd harmonics of the modulating frequency in an SSB RF signal.

I will also pick a nit with your statement that double-sideband wastes power. It DOES waste spectrum, exactly as you describe, but what I have noticed, using software-defined radio to listen into shortwave broadcasts, is that if you use SSB demodulation to detect an AM signal, you get a lower signal-to-noise ratio than you do when using a DSB demodulator. If you think about that for a moment, the reason becomes clear: by having energy in both sidebands, you are detecting twice as much energy for the same amplitude of signal, just because the DSB detector sums those energies together. So to get the same signal level from an SSB signal, you actually need twice as much energy in that one sideband. You might ask, doesn't the noise also get doubled as well, since your receiver bandwidth is twice as wide? The answer requires more math than I am prepared to present right here, but the noise in a receiver does not increase linearly with bandwidth, but as the square root of the bandwidth. So by using a double-sideband demodulator, you increase the sideband energy by 2, but the noise level by only 1.4 (square root of 2). So in practice, the much more significant advantage of SSB is about bandwidth conservation rather than power conservation.

Thank you again.

[johnling]

A lovely explanation, thank you-as a ‘returnee’ to Ham radio after 40 odd years, I need the cobwebs blowing away. All the info is in there..somewhere. This helped bring some of it back!

[manusudha]

Excellent useful lecture. Greatly appreciated.

[hennero.]

Thank you, Ralph. 🙂
Learning all this by means of self-study to pass a ham radio license test is one thing, watching your explanations with the actual signals both on the oscilloscope and the spectrum analyzer is another. The first one is just enough to pass the test, whereas the latter one is adding to the pieces of the puzzle that makes the background clear. 🙂
Especially what you said about the carrier that needs to be added on the receiver's side to have a _reference_ for the information in the side band which is otherwise unusable makes things somewhat more understandable for me (and as SSB is more or less the only mode I am using, I would like to understand more of a what my TRX is doing 😉).

[gregory-hmgm]

Thank you. What a brilliant explanation!

[aaronlindemann]

I’d really appreciate a video that covers the circuit theory around the balanced modulator. This video covers a high level overview but not a lot of the electrical engineering around component selection. A good video for its intended purpose.

[patrick]

Again, a very informative video on not-so-simple topics. Thanks for that!

[martyb]

This is great information and presentation. Thanks for making this video!

[margaqrt]

It is evident that you put a great deal of attention, thought and effort into your presentation. And it was a comprehensive refresher that I really enjoyed.

There is one question I have about SSB that I've never found a satisfying answer. And tonight I just re-created the experiment that illustrates my question:

Transmitting with a FT 747-GX into a dummy load and listening on an Icom 7300 (with headphones) on 80 meters I transmitted my voice in AM and SSB.

Comparing the two, AM has a noticeably higher audio quality. It sounds more rich, and I would not be surprised if more of the audio spectrum is being "captured" and "transported" on AM.

We know AM is about double the bandwidth of SSB modulation. But, as your video explains, each sideband in traditional AM is a mirror duplicate. And in AM, if I'm not mistaken, the detector diode of a basic receiver only cares about one of the sidebands.

For the human audio spectrum: 20hz - 20khz; it seems to me going from 3khz up to 6khz is a bit of a wider of a slice of it. But I'm not convinced it's the increased bandwidth that explains the better audio quality.

Is it this, or something else?

Thank you.

[ernestb.]

Great, short and clear. Of course, not in depth, but just to get me curious to find out more 😀

[shakamuni]

at the 5:40 mark you are talking about the right and the left of the carrier which I am deciding to call the base 1K "tone". My questions is the modulation seems to be about up and down in the amplitude and not left and right. Why are you saying left and right?

[byronpangburn]

Simply amazing explaination of SSB and easy to comprehend! I am now subscribed.

[Numberlead]

One of the earlier attempts to use the radio spectrum more efficiently. Now we have ctcss and other tones to help. Also trunking systems and other digital communication systems.

[cameronbegin]

Brilliantly clear video. Earned a subscriber!

[TymexComputing]

Thank you for John 3.16 and for Ainos (0:49 - Ainoses were a NATION, not a tribe, in Japan and eastern Asia - nationalized finally by Japaneese. I came here looking for ssb information - i am not even a licenced radio operator :)

[brothertyler]

Thanks for including Bible right in the channel.