FM stereo question

Humour me: I live in a large metro vicinity with a diverse radio selection. However, on some stations, which I know are or were previously in stereo, the stereo "indicator" light does not light up on my tuner. Are these now a stereo / mono hybrid signal? Fwiw, the light does engage still on some stations, but not all like it used to. These are classic rock/ community radio stations and not talk radio.

 

Maybe the signal to your tuner is weak and the tuner automatically switches to mono to improve the signal-to-noise ratio. I haven't heard of any hybrid signals. Where I live there is on mono FM station which has been like that forever. Everything else is stereo.

 

Thanks for responding. I thought about that, but the 2 strongest stations which I received in stereo for years no longer 'light up" in stereo.

 

Does it sound like stereo?

 

Good question! Sort of, some separation, but not like I'm used to.

 

Have clear channel/big classic rock stations abandoned true terrestrial stereo broadcasting?

 

Try your car radio and see if the stereo indicator goes on there on the same stations.

 

Check the station's web site or give them a call and ask if they are stereo.

 

There's not exactly a "hybrid" signal. FM Stereo is basically the original standard 1950s mono signal, for compatibility with mono radios, plus a weaker subcarrier (authorized in 1961) (it basically is received more weakly no matter what) that carries information to decode everything into real, true stereo. If you have a weak signal, the subcarrier might not get picked up, or your tuner may decide it is below its standard and stay mono.

At the station office end they make think they're sending out stereo, but out at the broadcast antenna which could be miles away, there may be some technical difficulty impairing the subcarrier for stereo, which the antenna guys don't want to report to the station. This is possible but not likely. Several stations may be sharing the exact same broadcast antenna and some equipment. The antenna location may even be unmanned some of the time.

But it's more likely there is a new building or construction going on where a high crane or something is in the way of the straight line from the broadcast antenna to you, reducing the level of the signal you're receiving, and your tuner is staying in mono. Or, a new tall building could be causing reflections or "multipath", confusing your home receiver.

Your tuner may have steps of using the subcarrier, to give full or less or no stereo separation depending on the level of subcarrier it's receiving. With a weak but present subcarrier, it would be possible to get full true stereo but it would be so horribly noisy that you would want mono anyway. Lower end tuners ignore weak subcarriers and stay mono below a certain signal strength and are just stereo "on" or "off". Better tuners may have a stepping system going from mono with a very weak subcarrier, to steps of some stereo separation but keeping noise down, to maximum separation when it has a strong subcarrier signal.

If you can, find the location of the antenna (the office can tell you), and drive by it, or just toward it, and hear if you get good stereo in your car. If so, at home you'll need to try a more sensitive and/or higher antenna, and in some bad situations you won't be able to fix it that way. If you're using an indoor antenna, move it around the room or into another room and even up and down, and that might help enough.

 

Thanks guys. I'm still a bit confounded, but I connected a backup tuner and that seems to be receiving stereo signals no problemo. It's technically an inferior piece, but until I solve the riddle, it's all I have!

 

Is it a public/community station? I know here in the SF/Bay Area, there is a public station that only broadcasts in stereo for music programs, mono for talk. Music programs are in the evening and on weekends, and the station does this to eliminate multipath programs and make their shows easily listenable in the car during the daytime, even though it's a tiny 1900 watts. So maybe your station is starting on something like this, or perhaps it's a cost issue?

 

If you have plenty of consistent signal strength, and your tuner does receive Stereo on at least something, call the station and ask to speak to the engineer or have the engineer call you, sometimes listener calls have gotten equipment problems to a priority and effort made to repair the equipment. Defective audio processors, stereo multiplex generators, or STL path can cause reversion to mono operation. Good engineers like to know if a listener has reception issues.

 

Thanks again! Well, I decided to send my old vintage Pioneer analogue tuner in for an "alignment". Not sure if this is the cause, but this doesn't cost much, and probably should have been done awhile back. I also included notes on my perceived issues. In the meantime, I have an 80s Denon digital back in service! Actually not a bad CL find. They are giving away tuners now, so hold out for a decent model. I prefer NAD, Proton, Sansui, Marantz, Sansui, Yamaha, etc.

 

Sounds like the internal potentiometer to adjust either the "STEREO THRESHOLD" or "MPX SEPARATION" has drifted out of alignment.