Does anyone have time to explain bandwidth of SSB transmissions

[YesterdayMan]

I thought I completely understood AM modulation since I learned about it in college 30 years ago, but now I have to question my understanding, since I've found several sources that explain the bandwidth of SSB transmission the same.

Please allow me to present an example that conveys my confusion:

A carrier signal of 20kHZ is used to transmit a 3kHZ sinewave. The receiver can reconstruct the sinewave from the amplitude of the carrier signal. Therefore, the bandwidth consists of only one frequency, 20kHZ. If we consider the 3kHZ sinewave that's being superimposed upon the carrier wave, we could say that in addition to the 20kHZ carrier wave, there is also a 3kHZ sinewave that rides upon the top of the carrier signal and a mirror image signal that's imposed upon the bottom. However, both the top and the bottom signals that are imposed upon the carrier frequency would be a 3kHZ sine wave. This 3kHZ sinewave, if it were transmitted with a higher frequency carrier wave, say 40kHZ, would have greater definition, but the same frequency, 3kHZ. The frequency of the transmitted signal is independent of the carrier frequency.

What I envision is 2 signals that could be drawn from the transmission. A 20kHZ carrier frequency, and the 3kHZ signal. There is nothing being transmitted at 10kHZ for instance. However, in the scenario I described above, if we were transmitting a 3kHZ signal on a 20kHZ carrier wave, using SSB, I believe the conventional wisdom is that the bandwidth would be 23kHZ. This doesn't make sense to me. We're not using 23kHZ of bandwidth. We're using one frequency only.

Can someone help me make sense of this?

Thank you,

 

[ve3lny]

I thought I completely understood AM modulation since I learned about it in college 30 years ago, but now I have to question my understanding, since I've found several sources that explain the bandwidth of SSB transmission the same.

Please allow me to present an example that conveys my confusion:

A carrier signal of 20kHZ is used to transmit a 3kHZ sinewave. The receiver can reconstruct the sinewave from the amplitude of the carrier signal. Therefore, the bandwidth consists of only one frequency, 20kHZ. If we consider the 3kHZ sinewave that's being superimposed upon the carrier wave, we could say that in addition to the 20kHZ carrier wave, there is also a 3kHZ sinewave that rides upon the top of the carrier signal and a mirror image signal that's imposed upon the bottom. However, both the top and the bottom signals that are imposed upon the carrier frequency would be a 3kHZ sine wave. This 3kHZ sinewave, if it were transmitted with a higher frequency carrier wave, say 40kHZ, would have greater definition, but the same frequency, 3kHZ. The frequency of the transmitted signal is independent of the carrier frequency.

What I envision is 2 signals that could be drawn from the transmission. A 20kHZ carrier frequency, and the 3kHZ signal. There is nothing being transmitted at 10kHZ for instance. However, in the scenario I described above, if we were transmitting a 3kHZ signal on a 20kHZ carrier wave, using SSB, I believe the conventional wisdom is that the bandwidth would be 23kHZ. This doesn't make sense to me. We're not using 23kHZ of bandwidth. We're using one frequency only.

Can someone help me make sense of this?

Thank you,

An SSB signal is not AM. There is no carrier and only one sideband. Using a 3KHz tone into an SSB modulator in your example will give you a CW signal of 23 KHz or 17 KHz depending on whether it is USB or LSB. From the receiver's point of view, there is only one signal to receive and no way to tell what the original modulating tone was. The bandwidth in this case is very narrow, as with receiving CW.

 

[BinaryMode]

And it's kHz...

I would try ChatGPT, Venice.ai or Claude. You can even roll your own with Ollama. There are Ollama GUI frontends.

The point is this: if you have questions, ChatGPT et al is like RadioShack +1,000,000.

It's helped me tremendously understand certain topics.

Anyway...

 

[K3YGX]

I trust "AI" as far as I can throw a loaded dump truck.
AM is 'double sideband with carrier - SSB is an upper or lower sideband with no carrier
Receivers filter out the opposite sideband and the BFO adds the 'missing' carrier
so it won't sound like a 'duck quack'

 

[BinaryMode]

Yeah, I don't trust it either. I certainly don't trust the companies behind it as well. But so far so good. And for the stuff I'm wanting definitive answers I do MY due diligence and double, triple or quadruple check.

Rolling your own AI with Ollama and a pretty decent GPU (Graphics Processor Unit) would be the way to go. Venice.ai seems a little more promising though, but I (disappointingly found) that ChatGPT and Claude are the better. Disappointingly in that I don't care for these companies and their money making, privacy invading tactics. Heck, as it is I don't even use Android but rather a third-party OS built from the Android Open Source Project called CalyxOS for what ever that's worth. Seems pretty good so far. I even run a heavily stripped down version of Winblows 10. 11? Won't touch that garbage with a ten foot pole.

But yeah, asking AI about SSB or AM or QPSK or OFDM, etc and it'll give you the lowdown without a doubt...

 

[dlwtrunked]

... If we consider the 3kHZ sinewave that's being superimposed upon the carrier wave, we could say that in addition to the 20kHZ carrier wave, there is also a 3kHZ sinewave that rides upon the top of the carrier signal and a mirror image signal that's imposed upon the bottom. However, both the top and the bottom signals that are imposed upon the carrier frequency would be a 3kHZ sine wave. This 3kHZ sinewave, if it were transmitted with a higher frequency carrier wave, say 40kHZ, would have greater definition, but the same frequency, 3kHZ. The frequency of the transmitted signal is independent of the carrier frequency.

What I envision is 2 signals that could be drawn from the transmission. A 20kHZ carrier frequency, and the 3kHZ signal. ...

This is technically not correct. There is no 3 kHz sine wave "above" your 20kHz signal (though the information for one is there). One can be recovered by demodulation though and that is what is done. If there were, and you removed the carrier (as done is a side-band receiver) and tuned there with an AM receiver, you would hear your 3 kHz sine wave but of course you do not (actually there will be a 23 kHz and not 3 kHz signal on the frequency and your receiver will see that as a dead carrier). Also, "rides upon." is not a technical term and thus vague at best and meaningless at worth. Same for "imposed upon". (And your "greater definition" sentence is just false despite the vagueness of "definition" and any reasonable meaning that you can put on that word.) Translating technical terms into such language is a bad idea. I am not trying to be over critical, just trying to say simplifying as you have done leads to inaccuracies and false conclusions that compound each other. It is best to stick with the technical descriptions, if simpler ones worked (which would be nice), we would all use them. But your question about why is the bandwidth 3 kHz instead of 23 kHz for your example signal is also indicative of the same problem. Your definition of "bandwidth" may be the problem. Yes the receiver has to be able to receive frequencies spanning around 23 kHz, but only those close to that because that is where your signal is.

 

[prcguy]

I think the key to understanding single sideband is to start with creating an AM signal as the OP says he is familiar with, which has a carrier, a lower sideband and an upper sideband, both which carry the same information, Then you filter out the carrier and one sideband leaving just the other sideband.

Most SSB transmitters create the AM signal and filter out the carrier and one sideband at a low frequency then translate that to the final operating frequency by mixing with other signals and filtering out unwanted mixer products to end up with the desired frequency. This allows the transmitter to be more frequency agile and not have a specific carrier and sideband filter for every frequency you want to use. The final filter that removes mixer products can be somewhat wide allowing the transmitter to operate within a range of frequencies for that one filter selection.

Newer transmitters are using SDR technology where a computer is creating a simulation of an SSB transmitter in software and creates the modulated RF carrier without using typical radio hardware.

 

[YesterdayMan]

I really do appreciate all of your input. The 23kHZ makes perfect sense to me for a frequency modulated signal and no sense at all to me for an amplitude modulated signal, which is why I asked the question in the first place. I only asked because I kept finding resources that discussed the SSB as though it were AM.

I first came across this at hamstudy.org, where the explanation for a question about SSB was asked. I typically will read the explanations for all the questions so that I can check my understanding. In this case the question was:

What is the approximate bandwidth of a typical single sideband (SSB) voice signal?

The correct answer is 3kHZ.

The explanation given is:

Single Side Band is a modified form of Amplitude Modulation (AM). Because AM has two mirror-image sidebands, it normally uses twice the bandwidth of the modulating signal. Because single sideband only transmits one sideband, its radio frequency bandwidth is equal to the bandwidth of the modulating signal. SSB also omits the AM carrier, but it does not consume any radio bandwidth.

A traditional communications-grade voice signal extends from about 300 to 3300 Hz, with newer transceivers using digital signal processing (DSP) extending the low end to about 100 Hz to improve fidelity. So the radio bandwidth of a SSB signal is very approximately 3 kHz.

As a memory aid, note that SSB has 3 letters, which is the same number of kHz as the bandwidth, 3 kHz.

As for using the correct terminology, I will as I become familiar with it.

Thanks,

 

[prcguy]

I really do appreciate all of your input. The 23kHZ makes perfect sense to me for a frequency modulated signal and no sense at all to me for an amplitude modulated signal, which is why I asked the question in the first place. I only asked because I kept finding resources that discussed the SSB as though it were AM.

I first came across this at hamstudy.org, where the explanation for a question about SSB was asked. I typically will read the explanations for all the questions so that I can check my understanding. In this case the question was:

What is the approximate bandwidth of a typical single sideband (SSB) voice signal?

The correct answer is 3kHZ.

The explanation given is:

Single Side Band is a modified form of Amplitude Modulation (AM). Because AM has two mirror-image sidebands, it normally uses twice the bandwidth of the modulating signal. Because single sideband only transmits one sideband, its radio frequency bandwidth is equal to the bandwidth of the modulating signal. SSB also omits the AM carrier, but it does not consume any radio bandwidth.

A traditional communications-grade voice signal extends from about 300 to 3300 Hz, with newer transceivers using digital signal processing (DSP) extending the low end to about 100 Hz to improve fidelity. So the radio bandwidth of a SSB signal is very approximately 3 kHz.

As a memory aid, note that SSB has 3 letters, which is the same number of kHz as the bandwidth, 3 kHz.

As for using the correct terminology, I will as I become familiar with it.

Thanks,

With the example of a 20KHz center frequency, if its modulated with USB it would still be a center tuning frequency of 20KHz but the modulation would occupy roughly 20 to 23KHz if it had a 3KHz band width and the lower audio frequencies would be on the 20KHz end and the higher audio frequencies would be near the 23KHz end.

If it was modulated LSB it would occupy roughly 20KHz down to 17KHz with higher audio frequencies being at the 17KHz end and lower audio frequencies at the 20KHz end like a mirror image of the USB signal. Modulating the same 20KHz center frequency with AM and a 3KHz audio band width would occupy roughly the entire 17 to 23KHz range or +/- 3KHz from center frequency.

 

[AK9R]

What is the approximate bandwidth of a typical single sideband (SSB) voice signal?

The correct answer is 3kHZ.

I don't think that question can be answered without knowing the bandwidth of the audio signal being used to modulate the RF. There are hams engaged in "expanded" or "extended" single sideband communications (sometimes abbreviated ESSB) where they use audio that's wider than 3 kHz. As a result, the resulting SSB signal is wider than 3 kHz.

Typically, amateur radio SSB starts with audio that is less than 3 kHz wide so the resulting RF signal is 3 kHz, too. For example, many late-model Icom radios cut off the lower end of the audio at 100 Hz and the higher end at 2900 kHz which results in an SSB signal that's 2.8 kHz wide.