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Single Sideband Suppressed Carrier (SSBSC) Video Demonstration

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Greater Media, in cooperation with Omnia Audio, conducted some on-air testing in Boston to compare the legacy DSBSC system vs. the proposed SSBSC (Single Sideband Suppressed Carrier) alternative for FM Stereo. Their chief engineer, Paul Shullins, drove a well known multipath challenging route within the coverage area of WMJX 106.7 FM, the Greater Media station there. He did something which further confirmed the testing. He ran video from the dashboard of his car and captured the audio. This validates the location of the captured off-air audio.

There are two videos back to back, about 30 seconds in length. They are taken from the exact same points along the route. The first one, dated November 15, 2011, is of the standard DSBSC stereo system, and the other one is taken the next day on November 16, 2011, using the SSBSC method.

http://www.youtube.com/watch?v=KlxeI2uqCOw
 
Very impressive! I hope that if a station tests this locally (Portland, Oregon) I get a chance to check it out.
 
I have to say, I'm impressed too. What is supposed to be the down-side of this?

Most modern processors have this option built-in, yes? If an older station wanted to "retrofit" their signal to do SSBSC (assuming the FCC approves it), would there be much expense or labor involved?

Anything that improves the FM stereo experience for listeners without requiring the purchase of a new radio, I am "for!" :)
 
NightAire said:
I have to say, I'm impressed too. What is supposed to be the down-side of this?

Most modern processors have this option built-in, yes? If an older station wanted to "retrofit" their signal to do SSBSC (assuming the FCC approves it), would there be much expense or labor involved?

Anything that improves the FM stereo experience for listeners without requiring the purchase of a new radio, I am "for!" :)
Click to expand...

So far, we have not, nor has any broadcaster who is using SSB, observed any downsides to it. If anything, there are probably some areas where the difference may not be as great. The areas where the overall RF signal is severely challenged to begin with.

Right now, Omnia.11 and Omnia.9 have the SSB option built-in. I believe the Optimod 8600 has it too. We'll be offering a stand alone stereo generator that will have the option for those who wish to retrofit older gear.

The labor involved to put SSB on the air is very intense!! It's a matter of selecting the option in the stereo generator menu!! :) Actually, that's all there is to it. Modulation level remains the same. There's no need to do anything differently at all other than a menu selection.

-Frank Foti
 
Frank,

Are you at liberty to explain your approach at controlling the inherent overshoots of SSB? I am aware that no standard exists, and each company may have some of their own "black magic." :-X
 
fm-engineer said:
Frank,

Are you at liberty to explain your approach at controlling the inherent overshoots of SSB? I am aware that no standard exists, and each company may have some of their own "black magic." :-X
Click to expand...

Actually, more is made out of this than needs to be. A SSB modulator can produce overshoots due to the angular filtering involved. The method used to control them is not much different than the inaudible method used to eliminate clipping overshoots in processor's low pass filter. Our approach manages the SSB modulator so that the spectrum remains clean, modulation is as tight as it is in DSB mode, and this is done inaudibly.

BTW: Both Omnia.11 and Omnia.9 handle SSB modulation control in an inaudible fashion. When A/B switching between DSB and SSB, you can not hear any difference to the audio, with regards to fidelity. If observing peak level on a scope or mod monitor, the modulation remains the same for either mode.

-Frank Foti
 
What's the FCC stance on SSB?
 
BobOnTheJob said:
What's the FCC stance on SSB?
Click to expand...

They want to know more about what happens when SSB is used. To that extent, any broadcaster can use SSB. All they need to do is obtain Experimental Authorization from the FCC. We have posted information how to do on the OmniaAudio.com website.

-Frank
 
satech said:
Does it reduce noise in stereo reception, or only when the receiver has already blended to mono?
Click to expand...

With an existing receiver that decodes a DSB mix signal, stereo S/N is the same.

But, when transmitting SSB, and the decoder in the receiver is only sensitive to SSB, there's a broadband noise improvement of 3.7dB. While that figure doesn't look like much, there's a hidden benefit. Due to the rise in noise across the FM channel, at 6dB/octave, and the lower sideband freq response going in the 'opposite' direction, there's an improvement of 10dB S/N at 15kHz!! The HF hiss, which is more perceptable and annoying, is further reduced. I've run the SSB decoder - realtime - in MatLab, and when switching between DSB and SSB decoding the hiss (HF noise) reduction is noticeable.

-Frank Foti
 
Frank, does the modulation level of the one sideband need to be 'turned up' to make up for the loss of energy in the missing sideband?
 
LA_Guy said:
Frank, does the modulation level of the one sideband need to be 'turned up' to make up for the loss of energy in the missing sideband?
Click to expand...

No. The lower sideband is increased by 6dB in order to maintain the 1:1 ratio of L+R to L-R. On account of this, mpx modulation levels are the same for DSB and SSB.

-Frank Foti
 
NightAire said:
What is supposed to be the down-side of this?
Click to expand...

1. Reduced stereo separation for any receiver with a nonflat IF passband (all analog receivers). I've calculated the 15-kHz separation for one of my high-performance tuners as 29 dB in wide-IF mode and 18 dB in narrow for an SSB signal. http://ham-radio.com/k6sti/SEP.ZIP The calculated figures for a DSB signal are 55 and 39 dB.

2. Incompatibility with any tuner, such as the Sony XDR-F1HD, that uses power in the 38-kHz quadrature channel to estimate stereo S/N. The SSB quadrature signal can fool a receiver into thinking that a perfectly clean signal is noisy or multipathy, which may cause the tuner to blend the signal to mono or mute it.

3. Incompatibility with any receiver circuit that relies on the vector sum of DSB sidebands to be nearly constant, such as this postdetection filter for HD Radio self-noise: http://ham-radio.com/k6sti/ibocfltr.htm. An SSB signal will yield a nonflat composite, which will reduce stereo separation.

Brian
 
FFoti1 said:
BobOnTheJob said:
What's the FCC stance on SSB?
Click to expand...

They want to know more about what happens when SSB is used. To that extent, any broadcaster can use SSB. All they need to do is obtain Experimental Authorization from the FCC. We have posted information how to do on the OmniaAudio.com website.

-Frank
Click to expand...
Can't find info that tells who to file the request with, what the request needs to say and the address it goes to. Can I get a URL for this? The boss wants me to proceed.
 
k6sti said:
NightAire said:
What is supposed to be the down-side of this?
Click to expand...

1. Reduced stereo separation for any receiver with a nonflat IF passband (all analog receivers). I've calculated the 15-kHz separation for one of my high-performance tuners as 29 dB in wide-IF mode and 18 dB in narrow for an SSB signal. http://ham-radio.com/k6sti/SEP.ZIP The calculated figures for a DSB signal are 55 and 39 dB.

2. Incompatibility with any tuner, such as the Sony XDR-F1HD, that uses power in the 38-kHz quadrature channel to estimate stereo S/N. The SSB quadrature signal can fool a receiver into thinking that a perfectly clean signal is noisy or multipathy, which may cause the tuner to blend the signal to mono or mute it.

3. Incompatibility with any receiver circuit that relies on the vector sum of DSB sidebands to be nearly constant, such as this postdetection filter for HD Radio self-noise: http://ham-radio.com/k6sti/ibocfltr.htm. An SSB signal will yield a nonflat composite, which will reduce stereo separation.

Brian
Click to expand...

I've discussed with receiver manufactures how they test decoder separation. They DO NOT calculate stereo separation based upon the IF response as you describe. They perform a complete end-to-end system test. The same as done by broadcasters. Some receivers *may* have a slight separation reduction at the very top end of the audio band.

The critical issue -if a receiver had reduced HF separation- is can this be perceived? If someone had to choose: yield a bit of HF separation and have less multipath, or keep the status quo and live with annoying multipath? It must be pointed out that most receivers stereo separation remains the same with SSB, and a few actually show improved separation response.

We are in the process of testing the other two points you mention, and will share the results. Thus far, we have not received any negative feedback regarding receiver incompatibility, as you described. Although we have received feedback from a number of stations who are now able to penetrate various areas of their service are, which were sketchy before.

-Frank Foti
 
FFoti1 said:
I've discussed with receiver manufactures how they test decoder separation. They DO NOT calculate stereo separation based upon the IF response as you describe.
Click to expand...

The composite signal passes through the IF filter before the stereo decoder sees it. Its response must be taken into account. For example, some receivers with two IF bandwidths reduce L+R injection to the stereo decoder in narrow so that it matches the reduced L-R level caused by the IF filter. If you don't do this, separation can easily drop to 20 dB in narrow. If the IF filter response didn't matter, why is this degradation observed? Why would manufacturers bother to include compensation circuitry?

I've included the source code for my program in the ZIP file. The calculations are simple and straightforward. You're welcome to inspect the code. If you find an error, tell me and I'll correct it.

I neglected to mention

4. Incompatibility with multipath monitor circuits that use the quadrature stereo channel, such as this one:
http://ham-radio.com/k6sti/qmm.htm

Brian
 
Brian,

Would you agree that receivers you mention in 2, 3 and 4 are quite rare, compared to the number of receivers that are in most of the cars (where 90% of radio listening takes place)?

Nevertheless, I would be interested if you have any suggestions how to perhaps alleviate some of the issues you mention?


Regards,
Goran Tomas
 
I believe this method is also going to be incompatible with analog decoders using the older non-PLL methods, like diode-ring demodulators and any other decoder made before PLLs became the standard in the mid to late 1970s. There are still quite a few older tuners out there. I recently fixed a friend's 1973 Pioneer receiver which he bought upon graduating law school. He still uses it nearly every day and refuses all attempts to upgrade to something newer because he likes the way this one sounds. On the other hand, a few million older receivers is a drop in the bucket compared to the hundreds of millions of active PLL decoders in use. Also, many people won't even notice if the audio isn't stereo, as long as the LED is lit.
 
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