I read an article that Omnia proposes an adjusment to the FM stereo standard. They claim that with tuners made since 1973 with PLL decoders you only need to use the lower sideband from 23-38 kHz of the L-R signal and ignore the upper sideband from 38-53 Khz. Is this going to make a real world improvement with less noise and mulitpath?
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New FM stereo Standard
- Thread starter mgpt6
- Start date
I don't know about the effect on multipath. Noise should be the same unless a receiver detects and then takes advantage of an SSB subcarrier signal. In that case, I calculate that LSB-only transmit and receive should increase S/N 3.7 dB. However, using the composite response I measured for one of my tuners (both amplitude and phase), I calculate that LSB-only stereo should degrade stereo separation at higher audio frequencies for analog IFs. For a typical wide IF filter, separation at 15 kHz drops from 55 dB for DSB to 29 dB for SSB. For a narrow IF filter, it drops from 39 dB to 18 dB, assuming the receiver uses a separate stereo separation adjustment for narrow. While I don't think these numbers would bother me much and I suspect most people wouldn't notice the separation loss, they might be enough to prevent general adoption of the method. On the other hand, if the gain in multipath performance were enough, a station might be willing to sacrifice some separation in the extreme treble.
What causes the separation loss for SSB is the slope of the composite response, which is due to the IF filters. The normal DSB subcarrier signal compensates for the slope by combining one sideband that is too low in amplitude and the other that is too high. It works kind of like the vestigial sideband system of NTSC TV. But SSB stereo can use only one sideband, and it is always too high (compared to the DSB level the stereo separation trimpot was adjusted for). The SSB system should work fine with receivers that use flat digital IF filters.
You can download the program and data files I used to generate the numbers here:
http://ham-radio.com/k6sti/SEP.ZIP
It is a DOS program. After unzipping, type SEP at the DOS prompt for instructions.
Brian
What causes the separation loss for SSB is the slope of the composite response, which is due to the IF filters. The normal DSB subcarrier signal compensates for the slope by combining one sideband that is too low in amplitude and the other that is too high. It works kind of like the vestigial sideband system of NTSC TV. But SSB stereo can use only one sideband, and it is always too high (compared to the DSB level the stereo separation trimpot was adjusted for). The SSB system should work fine with receivers that use flat digital IF filters.
You can download the program and data files I used to generate the numbers here:
http://ham-radio.com/k6sti/SEP.ZIP
It is a DOS program. After unzipping, type SEP at the DOS prompt for instructions.
Brian
A complete description of this proposal is shown at the link below, along with comments by Bob Orban and others. It should answer most questions...
http://www.radioworld.com/article/107858
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http://www.radioworld.com/article/107858
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k6sti said:
It needs to be pointed out the results Brian claims, are not a full systemic end-to-end test. That is where stereo separation is measured from the source, through the stereo generator, RF modulated, then demuxed and separation is measured at the receiver outputs. Brian has communicated his questions to me, and we will be evaluating his input during our in-depth testing.
If we wish to be fair about the SSB stereo transmission concept, it would make sense that we do testing to confirm/validate various claims, as compared to judging the topic via incomplete data.
-Frank Foti
I wish I had a way to generate an LSB-only signal so I could measure separation and check the calculations. If you have a 192-kb sound card, you can generate an LSB-only stereo signal with this composite stereo generator:
http://ham-radio.com/k6sti/stereo.exe
This DOS program will generate DSB or SSB test tones. Run them to an FM signal generator or FM exciter and then to a tuner or receiver.
Brian
http://ham-radio.com/k6sti/stereo.exe
This DOS program will generate DSB or SSB test tones. Run them to an FM signal generator or FM exciter and then to a tuner or receiver.
Brian
The document says the LSB-only scheme doesn't work with early non-PLL receivers. So how would my 1971 Bogen (with all discrete transistors, no ICs) react to one of these signals? Obviously the 19 kHz pilot tone is still there, so it would trigger into stereo mode, but would it recover any trace of stereo separation? Or some kind of ugly noise/distortion in the L-R channel? Or just mono audio?R. Fry said:
Frank Foti,
I was doing some research and I couldn't figure out why the LSB L-R subcarrier couldn't be demodulated by a pre-1973 tuner.
I have an HH Scott model 350 FM tuner. It's a tube-type tuner which was built in 1961 or early 1962.
I'm going to build a stereo generator which outputs a 38kHz LSB stereo subcarrier.
I'd like to hear how the old HH Scott tuner handles the signal.
I'll post the results of my tests.
I was doing some research and I couldn't figure out why the LSB L-R subcarrier couldn't be demodulated by a pre-1973 tuner.
I have an HH Scott model 350 FM tuner. It's a tube-type tuner which was built in 1961 or early 1962.
I'm going to build a stereo generator which outputs a 38kHz LSB stereo subcarrier.
I'd like to hear how the old HH Scott tuner handles the signal.
I'll post the results of my tests.
Thanks Frank. That will save me a lot of work. Building a LSB Stereo Generator isn't a small job ... as you well know.
frankberry said:
Group,
Please know...we're doing this, in hopes of something that may better the tech in our industry. We've got no secrets, and the results of this idea are still an unknown. Together, we'll all learn something one way or another. Hence, what we gather, will be shared with this group, as well as the industry as a whole.
-Frank Foti
If it works properly on nearly all radios out there, It'll be a real help to some smaller broadcasters that have little rim-shot stations, etc. I know of a few that run mono right now to help with their signal issues. I'm guessing this LSB deal could help them stay in stereo but with more range. Thanks for taking time and resources to figure this one out Frank!
Does this only help S/N ratios on stereo signals, or can it have an impact on mono signals, too?
I'm suspecting it wouldn't impact mono at all based on my limited understanding of what's being proposed; if that's true, if this would bring stereo FM to parity with mono regarding its noise floor, I can't imagine why ANYONE would operate in mono anymore... even the tiny LPFMs around here.
The LSB-only scheme would not affect mono signals. It would not increase stereo S/N unless receivers were designed to detect and take advantage of the signal. In that case, I calculate that it should increase S/N 3.7 dB. That goes some way toward neutralizing the 20-dB stereo S/N penalty. The improvement would be noticeable but not earthshaking.
The Sony XDR-F1HD and Carver TX-11b tuners use noise reduction systems that make a real improvement in stereo S/N. I've analyzed both here:
http://ham-radio.com/k6sti
I often listen to NPR voice programs in mono to improve S/N from distant stations. The programs normally have little or no stereo content. A 35-watt NPR station I listen to transmits only in mono. Another station transmits NPR programs in mono during the day and switches to stereo at night for music broadcasts and on weekends for NPR variety programs.
Brian
The Sony XDR-F1HD and Carver TX-11b tuners use noise reduction systems that make a real improvement in stereo S/N. I've analyzed both here:
http://ham-radio.com/k6sti
I often listen to NPR voice programs in mono to improve S/N from distant stations. The programs normally have little or no stereo content. A 35-watt NPR station I listen to transmits only in mono. Another station transmits NPR programs in mono during the day and switches to stereo at night for music broadcasts and on weekends for NPR variety programs.
Brian
Stereo vs Mono operation makes little difference on radios with a Mono switch. But stations in stereo will have much greater multipath issues on receivers that always listen in stereo. News talk stations with no stereo content and the silence between words benefit most from mono operation. Another area where I've used mono operation is where translators are picking up a weak signal. Operating the station that is being translated in mono has made the difference between a signal that sound pretty good & one that sounds so bad that no one would listen to it. Stereo is great, but it has it's limitations. Playing the mono card has it's benefits at times.NightAire said:
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