Why We don't look at Single Side Band in the Time Domain (#452)

Dave Casler here to help show and explain why we don't look at the Time Domain when using Single Side Bands.


Edited by Callum Jakeman


Theme music is "Sour Tennessee Red," by John Deley and the 41 Players, courtesy YouTube Music Library.



Twitter: @dcasler

[marklundeberg]

In short, the problem is that the signal envelope is only a part of the SSB time domain signal. To get the full information you'd have to show also phase relative to carrier, or better yet decompose into the two quadratures (one of them is the signal exactly). But either is a way more complex thing than a plain envelope!

Still I think for anyone going beyond basic understanding of signals, it's always good to keep in mind the real time domain. A frequency-only understanding is an incomplete one.

(Thank you for making this video. I had exactly this same question and this helped me a bit to wrap my head around the answer.)

[paulmitchell]

Dave, missed a great opportunity to explain the relation of time domain to frequency domain being othogonal. (!!!)
Take a time domain rf signal (sine wave or envelope) turn it by 90 degrees - look at it from the side (in manner of speaking) - viola - you're in frequency domain!!! try and wrap your mind around it. My microwave professor in college had a visual aid made out of wooden sinewaves to help explain it (he was a radar engineer) it blew my mind.

[BryanTorok]

Fifty-some years ago, at about 13 or so years old, I visited with a the father of classmate who was a Ham. I was fascinated. I wanted to be a Ham and get a Technician license because to my mind and experience anyone who was a technician was a well respected professional in electronics.

He tried to explain SSB to me. I knew what a sine wave looked like on an oscilloscope and understood AM modulation. So, I kept trying to get him draw me what a SSB signal looked like. I kept trying to figure out what part of the sine wave was missing. I'm sure I didn't understand terms like time-domain and frequency-domain. It ended up with us both being frustrated and him thinking I was an idiot know-it-all. I had a similar low opinion of his teaching skills.

Even after seeing Dave's demo, I'm not sure I understand why the time domain display of a SSB signal looks like it does. I'm going to have to perform my own experiment with different tones for modulation and see what it does.

First I have to fix my 60 year old 'scope or just buy a new one. I'm amazed that scope Dave used is available on eBay and Amazon (new, shipping included) for $350. 20 years ago, a scope with those capabilities would have cost ten times as much.

Now I have to hit Dave's tip jar.

[billharris]

Hi Dave, the SSB waveform can clearly be seen on an oscilloscope when using a 2-tone test, where audio frequencies in the SSB audio pass band are inserted into the microphone input, typically 400 and 1, 800 Hz, which is commonly used to measure the linearity of the RF Power amplifier in the transmitter. If the audio tones are exactly at the same amplitude, you will see a waveform that somewhat resembles AM, except the valleys of the signal actually go to zero. The apparent modulation on the oscilloscope will be at a frequency that is the difference between the 2 tones.

73, de AC8AQ

[tristanmills]

I'm enjoying these q&a episodes. There's always something to learn from people's questions

[DennisSantos]

I'm confused. If we zoom in on the AM time domain waveform we can see the RF (carrier) frequency. What will we see if we zoom in in the SSB time domain waveform?

[miker]

I think I would have liked to see what a simple voice audio waveform looked like.
Watched this twice. Maybe you could explain what the SSB wave is actually showing/doing at the peak and dip. I’d really like to understand this but I don’t.
73

[wbeaty]

Hold on hold on. That's not the upper sideband waveform. (Or does USB WAVEFORM actually mean universal serial bus, not upper sideband?) That's a carrier-suppressed or DSB waveform, where the audio modulation crosses zero and goes negative. (Take the AM modulation, then subtract the carrier. That's the same as moving the zero-ref of the cpo tone downwards, so the lower peaks go negative at the modulator output, which, in those places gives us high-freq sine, with negative polarity.) But that's not ssb, not a "USB waveform, " instead it's carrier-suppressed only. It's DSB.

The SSB upper sideband should look like a 10800KHz CW sinewave, with some slight distortion since the cpo signal isn't pure 800Hz sine. (Take the CW CPO waveform, and uniformly increase its frequency by 10x. It will still appear to be CW on the scope.)

[vjdav]

Nice way to discuss this topic as you have done here Dave! Enjoyed it.

[johngrwf]

, So good I watched the video twice. Took me back to my military training nearly 40 years ago...

[HobbyHalloween]

WOW Very interesting! Hey Dave: You brought up a great topic/question to ask: The difference of adding vs. mixing a signal... I've seen this on audio forums for mixing sound sources and the discussions blurred so not sure who is right anymore. Thanks and 73's

[Spookieham]

I've dropped more or less every single other Amateur Radio channel because they are clowns ( Dx Commander is a prime example), people shilling equipment or morons talking about things they don't understand.
However Dave is still on my list because I learn at least something new or useful in EVERY single video. Thanks Dave

[watthairston]

Very good explanation of a complex topic Dave! Phase sensitivity of the human ear very different person to person and baffling as to how it is resolved or perceived.
Thanks so much for another very interesting topic and post.
73' de K4WRF

[dominickzappola]

Very cool. Need to do more of this. Nice job on it.

[davemaier]

You are just awesome! Thank you for all your informative videos.

[Mike-H_UK]

Very informative & well presented. Thanks!

[markjames]

I liked the explanation of phase distortion in SSB.

[martinchristiansen]

This was clearly the most interesting video for a very long time - very, very good! But how I wish that you had used the same, pure sine wave for modulation instead of that square wave from the cw training kit, in order to provide direct comparison with the corresponding AM and FM signals. I still wonder what the SSB modulated signal would look like in that case. Could you please, please use your scope again and show us?

[johnbeckham]

Well, David, you have me wanting to go out and buy the new Sihuaudon D-808 by Radiwow with RDS on the FM and of course SSB! Thank you, David!

[tmatheson]

As usual Dave you are very precise and make it interesting. Nice OM OG! 73s.