Does anyone have time to explain bandwidth of SSB transmissions

[mayidunk]

The power is determined by the carrier. At 100% modulation the PEP will be 4x carrier power. You can achieve 100% PEP with a single tone but it won't use the entire available audio bandwidth that the modulator is set for.

You need to think in terms of looking at this on an oscilloscope, not what you see on a waterfall or frequency spectrum display.

I get that. What I was always trying to wrap my head around was the concept of how the sidebands would contain the two component parts of speech or music, which are made up of many different frequencies that are spread out across the bandwidth, along with their individual levels. Does that make sense? I'm thinking more in terms of the theory, as opposed to the practical.

Consider what you'd have in each sideband if you were to modulate the carrier with a white noise signal, where each frequency in the white noise was at the same power level. That's what I've been unable to conceptualize until I really started looking at the waterfall spectral display on my receiver. It got me thinking about it tonight, after having it pointed out to me about my error in saying that the loudness, or amplitude of the modulating signal determined the bandwidth. I started thinking about the spectral display on my radio, and I think I finally saw what I had been missing for so long about all this. I finally saw in the spectral display what I couldn't see in my head for so long! And, it really should have been obvious to me knowing that, if a modulating signal of a single frequency can produce sidebands of a single frequency, that that same modulating signal made up of many different frequencies will produce sidebands with corresponding frequencies, each individual frequency spread across the bandwidth of the sidebands that the modulating signal creates that, when the two sides are added together, comprise the entire bandwidth of the AM signal. Does that make sense?

I think my brain just cramped with that one!

 

[AC9KH]

Despite the brain cramp you pretty much got it

The spectral display is nice to see the modulated audio frequencies in the sidebands if you zoom in on it. Depending on what radio you got you can even transmit into your dummy load and use a tone generator to see this and watch the spike move across the display as you increase the audio frequency.

 

[mayidunk]

Despite the brain cramp you pretty much got it

The spectral display is nice to see the modulated audio frequencies in the sidebands if you zoom in on it. Depending on what radio you got you can even transmit into your dummy load and use a tone generator to see this and watch the spike move across the display as you increase the audio frequency.

Thanks. This has always been kinda like knowing the melody, recognizing it when you hear it, but never really hearing all the words in the song no matter how many times you hear it! Frustrating, but I could always work with it in spite of that.

 

[AB5ID]

Consider what you'd have in each sideband if you were to modulate the carrier with a white noise signal, where each frequency in the white noise was at the same power level.

Even though White noise is made up of all frequencies it's still limited to the bandwidth of the circuits that it passes through. That bandwidth for SSB will typically be 300hz-3000Hz, which is what is needed to carry a intelligible human voice.

 

[mayidunk]

Even though White noise is made up of all frequencies it's still limited to the bandwidth of the circuits that it passes through. That bandwidth for SSB will typically be 300hz-3000Hz, which is what is needed to carry a intelligible human voice.

Thanks for pointing that out, I can appreciate the need for intelligibility, and conservation of spectrum, over fidelity.

 

[mayidunk]

This is only indirectly. The AM modulator actually determines the bandwidth. AM takes a low frequency sine wave like audio and imposes it on a high-frequency carrier, which changes the amplitude of the carrier. The width of the signal is determined by the high and low cut of the modulator. The wider the high cut filters in the modulator, the more audio-frequency information it can carry.

Typical spoken voice on the air is going to carry from about maybe 250 Hz to 3,000 Hz audio. But this is like a two-lane freeway. Those two lanes can carry your cars, increase the width of the freeway to 8 lanes and it can carry more cars going at 8 different speeds. So by widening the filter in the modulator you can now stick 10K audio on that AM signal and make it sound more natural because most humans can hear up to 20K audio.

So it's actually the high and low cut filter in the modulator that will determine bandwidth of the envelope.

Practically speaking, you are correct, in that, the equipment that generates the modulated RF signal can limit the highest and lowest frequency of the modulating signal, thus directly controlling the bandwidth of the signal radiated.

However, apart from the limitations of the equipment involved, you can theoretically modulate a carrier with a signal with a very wide frequency response, which would result in a transmitted signal which will use an extremely wide swath of the RF spectrum.

 

[AC9KH]

I just did a little demo with the 7300's audio scope. The left side of the display shows where a particular audio frequency is modulated in the passband. The scope is set to 30dB on the y-scale, 4ms on the x-scale. The amplitude of the sine wave (audio drive) is shown on the scope, The frequency is on the x-scale (or time scale). When I talk you can see the complex, or composite, waveform that is imposed on the AM carrier by the modulator. The modulator simply steps the audio frequencies up to radio frequency and the demodulator does the opposite. A blade of grass or even a hot dog can become a demodulator by using the plasma arc to step the RF down to audio frequency as shown in the second video.

IC-7300 Audio Scopevimeo.com

 

[dlwtrunked]

This is only indirectly. The AM modulator actually determines the bandwidth. AM takes a low frequency sine wave like audio and imposes it on a high-frequency carrier, which changes the amplitude of the carrier. The width of the signal is determined by the high and low cut of the modulator. The wider the high cut filters in the modulator, the more audio-frequency information it can carry.

Typical spoken voice on the air is going to carry from about maybe 250 Hz to 3,000 Hz audio. But this is like a two-lane freeway. Those two lanes can carry your cars, increase the width of the freeway to 8 lanes and it can carry more cars going at 8 different speeds. So by widening the filter in the modulator you can now stick 10K audio on that AM signal and make it sound more natural because most humans can hear up to 20K audio.

So it's actually the high and low cut filter in the modulator that will determine bandwidth of the envelope.

 

[dlwtrunked]

When you say "amplitude of the carrier", if you mean power for the carrier, at 100% modulation, the carrier average power will be 2/3 of the average transmitted power.

And one thing is being ignored, we are really concerned about receiving, for optimum reception, we only want to receive bandwidth consistent with the intended signal. If the AM modulated is wider, receiving a wider bandwidth only adds noise and is non-desirable. So when discussing the bandwidth, it is that bandwidth that really should be considered.

And no, most humans "cannot hear up to 20kHz"--children can typically hear . An adult my hear 15kHz, in their 50's that drops usually to about 12kHz and some senior citizens hear will below half to this (I wish I could hear, 20kHz but my limit is 4 or 5 kHz--although a significant loss it frequency response, I do not really notice it at all.

 

[AC9KH]

And no, most humans "cannot hear up to 20kHz"--children can typically hear . An adult my hear 15kHz, in their 50's that drops usually to about 12kHz and some senior citizens hear will below half to this

You are correct, of course. Maybe I should've said the potential human hearing range is considered to be 20 to 20,000 Hz. The "useable" frequencies are more like 250 to 8,000 Hz.

Per your comment on the bandwidth, it takes more power to shove a wider signal at the same S/N. But 2.9 khz SSB or 6 kHz AM doesn't have the audio "punch" of 100% modulated 20 kHz AM broadcast. Those lower audio frequencies are more easily lost in the noise. This is why when you tune in WWV on a frequency with a marginal signal you may not be able to hear the 40 millisecond "ticks" but you can plainly hear the 440, 500 and 600 Hz tones, and the 600 Hz tone is usually more audible than the 440. A female voice usually carries more audio "punch" than a male voice. This has been known for centuries with the ancient Swedish herding call (Kulning) where it is typically an art mastered by women. A woman's voice will carry for incredible distances and the livestock would respond to it. It was even used in ancient times as a form of communication between Swedish villages, strictly done by women. Men have never been consistently successful at it.

 

[dlwtrunked]

You are correct, of course. Maybe I should've said the potential human hearing range is considered to be 20 to 20,000 Hz. The "useable" frequencies are more like 250 to 8,000 Hz.

Per your comment on the bandwidth, it takes more power to shove a wider signal at the same S/N. But 2.9 khz SSB or 6 kHz AM doesn't have the audio "punch" of 100% modulated 20 kHz AM broadcast. Those lower audio frequencies are more easily lost in the noise. This is why when you tune in WWV on a frequency with a marginal signal you may not be able to hear the 40 millisecond "ticks" but you can plainly hear the 440, 500 and 600 Hz tones, and the 600 Hz tone is usually more audible than the 440. A female voice usually carries more audio "punch" than a male voice. This has been known for centuries with the ancient Swedish herding call (Kulning) where it is typically an art mastered by women. A woman's voice will carry for incredible distances and the livestock would respond to it. It was even used in ancient times as a form of communication between Swedish villages, strictly done by women. Men have never been consistently successful at it.

Your first sentence is, of course, true. But in what follows, one should note that most 2.9 kHz or similar SSB filtering often also suppresses the audio below 400 Hz or so, as voice does not need it (and for voice it is more like interfering noise).

But AM is often music so the filtering for that generally tries to keep lower frequencies and desires to sound natural. I am listening to WWV now and no matter what bandwidth whether AM or SSB (I am using USB), I hear the ticks just as well regardless of the bandwidth. (I was listening to WWV at 8 minutes past the hour to hear the tests at that time.) I think your observation on this may be due to the type/model of receiver you use and be a factor in you observation. If there is a "punch" wider bandwidth signal AM signals, it is its own signals suppressing hearing other weaker signals or static in the bandwidth (particularly if AGC is engaged). (Not the same as FM capturing a signal but rather the effect of hiding other signals with one's own noise).

Regarding human voices, hearing a women's voice differently is not an audio thing but a brain thing as recent research shows. It's official! Listening to women pays off › News in Science (ABC Science)

 

[AC9KH]

Your first sentence is, of course, true. But in what follows, one should note that most 2.9 kHz or similar SSB filtering often also suppresses the audio below 400 Hz or so, as voice does not need it (and for voice it is more like interfering noise).

I think typical with sideband, the lower cut is usually 100Hz, the upper is 2900 so transmitted audio is 2800 Hz. Icom pretty much established this. And in lower-end radios I must admit that it's really hard to beat the transmit audio quality of a IC-7300. But if you use a tone generator and test this as per my little demo, you'll find that. a 7300 actually will modulate 3200 Hz audio. They use a soft-edge filter and I think this is why the radio sounds so good on sideband.

My FlexRadio OTOH, set to the same settings, has a brick wall filter and it won't even modulate 2930 Hz if the cut is set at 2900. But frankly, the Icom sounds better on sideband.

On AM it's the other way around. The 7300's lack of a 8 or 10 band equalizer and limited filter adjustment hurts it and it still sounds like a sideband radio on AM. If you want to play with the guys running 12 kHz AM on 160, may as well forget it with the Icom because it can't do it.

With the voice tone of a woman vs man, the ancient art of Kulning relies on the echo in the hills and valleys of northern Sweden, and the woman's voice will carry sometimes up to 8km. The man's voice won't carry that far with the echos and men have never been successful at it. It is kind of a lost art today, but a few women in northern Sweden still practice it.

 

[AC9KH]

i will add that the specific tones used in Kulning were developed or discovered over centuries to use tones that carry long distances. It uses tones up to 16 kHz. Most modern singers can't duplicate it without coaching and practice to achieve the specific melody of tones. There's somewhat of a scientific explanation on the wiki as to what makes it work. But I think this also applies to radio with audio frequencies that will "carry" vs being lost in the background noise.

Kulning - Wikipedia

en.wikipedia.org