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Any benefit to keeping FM stereo pilot on w/ mono programming?

G

GeneSavage

I've seen a couple of local FMs which air NOTHING in stereo... I mean NOTHING. One is sports / talk & even the bumpers are mono & half the programs are fed over raw phone lines; the other is a news / talk who may have stereo sources but either their board is set to mono or it's being fed to the processor in mono because there's zero separation on anything, bumpers, spots, etc.

BOTH of these stations are sending the 19KHz pilot, allowing plenty of multipath & hiss on the fringe of their signals.

Is there ANY benefit to leaving the stereo pilot lit? I heard somebody claim once some radios wouldn't stop on seek on stations without a stereo pilot, but I've never seen that behavior in ANY radio I've ever used & think it's balderdash. The local NPR affiliate switches off the pilot during mono programming, and it's a great help.

So... other than seeing the little "ST" light come on when you hit the station, is there ANY reason for these stations to be operating in "stereo" if they have no & will not have any stereo program material?

Thanks in advance for your expertise!
 
There's only 1 benefit I'm aware of...if you shut off the pilot, the phone will ring several times a week with some variation of "ya know that y'alls stereo light is burned out?" on the other end. Aside from minimizing those nuisance calls, I know of no reason to operate that way, but there are reasons to operate without the pilot...just look at Class C WSGS in Hazard,KY...HUGE signal in a mountainous area...plays lots of music & no stereo pilot. Mono does a better job in multi-path prone areas & the eastern KY mountains fit that definition well.
 
I think at one time radios did differentiate stations with the pilot, but I haven't owned a car radio for years that cares. A big disadvantage of the pilot when programming in mono is that the pilot is required to be between 8 and 10 %. That reduces the available modulation.
 
At one time, I am almost certain that FM stations transmitting in stereo were required by FCC rules to turn off the subcarrier during mono programming that lasted more than 5 minutes. I worked at WVUD-FM (now WLQT) in Kettering/Dayton, OH at the time. While our music programming was in stereo, we took the ABC FM Network News in MONO at :15 after the hour. It lasted only 5 minutes, so we kept the stereo going. But during times of public service and religious programming (Sunday mornings), we turned the stereo OFF. I believe this was (and may still be) an FCC requirement as all of us working there at the time had this pounded into our heads. I know for sure that many stations still liked to keep the pilot lights lit, however, Stereo or not! ...And still do. WSGS in Hazard, KY mentioned above, transmits only in MONO and it sounds good, even at great distances from their transmitter.
 
KR4BD said:
At one time, I am almost certain that FM stations transmitting in stereo were required by FCC rules to turn off the subcarrier during mono programming that lasted more than 5 minutes. I worked at WVUD-FM (now WLQT) in Kettering/Dayton, OH at the time. While our music programming was in stereo, we took the ABC FM Network News in MONO at :15 after the hour. It lasted only 5 minutes, so we kept the stereo going. But during times of public service and religious programming (Sunday mornings), we turned the stereo OFF. I believe this was (and may still be) an FCC requirement as all of us working there at the time had this pounded into our heads.
Click to expand...

Agreed, I'm 95% sure there was at one time a FCC regulation requiring the pilot be turned off during mono programming. Unfortunately that rule is not among those excerpted in old Yearbooks so I can't prove it...

73.297 is the modern rule covering stereo FM. Neither it nor the 73.322 and 73.1590 it references say anything about killing the pilot during mono programs.
 
I could be wrong, but I believe WTOP FM in Washington, DC at one time had turned off their stereo pilot. Don't know what the current status is. Not only does it give more clarity in multi-path prone areas, but seems to add an extra 10-20 miles of coverage area in the fringe.
 
KR4BD said:
At one time, I am almost certain that FM stations transmitting in stereo were required by FCC rules to turn off the subcarrier during mono programming that lasted more than 5 minutes. I worked at WVUD-FM (now WLQT) in Kettering/Dayton, OH at the time. While our music programming was in stereo, we took the ABC FM Network News in MONO at :15 after the hour. It lasted only 5 minutes, so we kept the stereo going. But during times of public service and religious programming (Sunday mornings), we turned the stereo OFF. I believe this was (and may still be) an FCC requirement as all of us working there at the time had this pounded into our heads. I know for sure that many stations still liked to keep the pilot lights lit, however, Stereo or not! ...And still do. WSGS in Hazard, KY mentioned above, transmits only in MONO and it sounds good, even at great distances from their transmitter.
Click to expand...

This was in fact the case up until about 1983 and there was a five minute limit, was a check and time entry on the transmitter log as well to indicate it had been done. Back in the early 70’s actually got a citation when it was left on for the thirty minute news block from 5 to 5:30PM. This was a very common citation in those days and it was beaten into every ones head. No big deal given the meters had to be read and logged every thirty minutes as well.

Can you imagine trying to get people to do that today?

w/
 
Leaving the pilot on while running mono programming is about the worst thing you can do. Remember that stereo is made up of two things-L+R (mono) modulating the main FM carrier and also L-R which modulates a 38 kHz suppressed carrier AM signal. When you leave your pilot on, you force the receivers' stereo decoder into adding that (now completely) unmodulated AM carrier back into the mix. Any noise on that carrier's signal will be added back into the final audio coming out of the receiver. The noise on this carrier is why stereo FM is always noisier then mono FM-and that's when stereo information is modulating the AM subcarrier. The noisest that FM can be is when you have 100% mono on a stereo signal. Cutting off the pilot forces the stereo decoder in the receiver off and (as another has commented) also gives back the 8-10 percent of modulation that the pilot takes away.

In the past, some receivers were set upthat when they were scanning they did not stop on mono signals. This has largely disapperared today-so thats's no reason to ever leave your stereo pilot on when running mono programming. My XM radio's FM modulator even switches to mono when it finds a channel in mono (like the traffic and sports channels).
 
You gain slightly less thna 20 dB S/N in mono, which equates out to substantially greater coverage. We used to originate a major SEC football team.. had to remember to turn the 19KHz off for games. The limit was why we never did more than two minutes from a remote, plus a 2 or max 2 1/2 stopset.
If you're running spoken word and a pilot, you're doing your owner - and yourself - a disservice.
 
A little off topic, but it is curious to note that many B/EZ stations in the 70's and 80's used to air their spots in MONO for effect. Don't know what the evidence was behind that, but I thought it was an interesting idea.
 
I think beautiful music stations MIGHT have done their spots in mono to keep them as low-key as possible... they didn't want the spots "jumping out" at the listener, as evidenced by some of the B/EZ programmers who insisted the spots be X-number of db below regular programming.... great for the listener, seems like it would be bad for the advertiser.

Now that I think about it, there are THREE FM stations in the area with all-mono programming, all running in stereo. We've got a Bott radio affiliate (preaching / teaching), a local sports / talk, and a conservative news / talker.

Anybody remember which radios wouldn't stop on an FM signal without a pilot, and why? It seems like it would be easier to detect carrier than pilot, or at least as easy (not knowing a darn thing about how seek / search functions on radios work).

Thanks for the education! This is all very interesting to me.
 
One consideration for running the stereo pilot 24/7 would be having RDS. I don't think you can have RDS without the stereo pilot to lock to.
 
B/EZ station I worked on/for didn't do stereo commercial because the expense of stereo Insticarts was ridiculous. I get ill just thinking about keeping 192 stereo heads aligned. That station kept its' pilot on all the time. That RCA stereo generator made a big "pop" when it switched.

A University FM station here has been mono since it went on. A cost and programming decision since it’s mostly talk. Their HD is also “mono”.

Come to think about it, the mono Insticarts were also way too expensive.
 
Is the coverage the same if a station broadcasts no stereo pilot, versus a radio with the stereo/mono switch set to mono?
 
If I'm not mistaken, Nick, what you're asking is if you get the same perceived increase in reception distance by using the stereo / mono switch on your radio vs the station switching off the stereo pilot.

In my experience, it depends on the radio. The stereo setting next to my computer, which switched to mono, cleans the signal right up. Believe it or not, I've had at least one radio which, when you switched to mono, simply COMBINED THE (noisy) STEREO CHANNELS! I don't know who thought THAT was a helpful design... but it's NOT!

In my car, I have no stereo / mono switch, meaning I'm at the mercy of the station... meaning the 3 local mono programming FMs all spit, slur, and in some cases become too hissy to comfortably listen to... all so the "ST" light will come on...
 
NightAire said:
If I'm not mistaken, Nick, what you're asking is if you get the same perceived increase in reception distance by using the stereo / mono switch on your radio vs the station switching off the stereo pilot.

In my experience, it depends on the radio. The stereo setting next to my computer, which switched to mono, cleans the signal right up. Believe it or not, I've had at least one radio which, when you switched to mono, simply COMBINED THE (noisy) STEREO CHANNELS! I don't know who thought THAT was a helpful design... but it's NOT!

In my car, I have no stereo / mono switch, meaning I'm at the mercy of the station... meaning the 3 local mono programming FMs all spit, slur, and in some cases become too hissy to comfortably listen to... all so the "ST" light will come on...
Click to expand...

Most modern car radios (and others as well) blend to mono when the signal goes below a pre-determined level. That tends to make the mono-stereo question a moot point. If you want to run RDS, you will need a 19KHz pilot. I've experimented both ways with our signal challenged LPFM. As far as I can tell, our listeners prefer seeing a stereo light. Those that are close enough really do get stereo. The rest get mono, but seem happy. YMMV
 
One consideration for running the stereo pilot 24/7 would be having RDS. I don't think you can have RDS without the stereo pilot to lock to.
Click to expand...

I can help you with that: RDS absolutely does *not* need the pilot to work, on either encoders or receivers.

RDS encoders have a pilot-sync input to phase-lock the RDS to the pilot when composite stereo is being used, e.g. the pilot is on. The thinking is to run the peaks of the RDS carrier at 90 degrees to the pilot, so that the zero-crossing of the RDS peaks occurs at the peak of the pilot.

Out in the real world, if you use any type of "peak-holdoff" modulation monitor (I'll pause while some say "what's that?") you'll never be able to tell the difference whether the RDS carrier is locked at 90 or zero degrees to the pilot, or whether it is locked or not, or frankly whether it is injected or not.

In re mono: do it! I was CE at the Howard Stern (I pause again for "what's that?") affiliate in New Orleans, and we made sure to drop into mono for his show. It greatly helped cover interference from the brutal Gulf tropo skip, and it really made Stern and his 30-minute commercial breaks LOUD!

Paul E. Burt, Chief Engineer
Alert FM, an RDS-alerting company
Baton Rouge, LA / Jackson, MS
 
Doctor_Technical said:
In re mono: do it! I was CE at the Howard Stern (I pause again for "what's that?") affiliate in New Orleans, and we made sure to drop into mono for his show. It greatly helped cover interference from the brutal Gulf tropo skip, and it really made Stern and his 30-minute commercial breaks LOUD!
Click to expand...

Well, maybe I'll try it again. I'm in East Texas, and the tropo/skip is brutal this time of year. In previous tests, I have been unable to discern much difference other than listeners seem to like to see the stereo light. We rebroadcast on several translators and use RDS to control them. If they work without the 19KHz pilot (which the instructions seem to think they need) then so much the better.
 
So basically what you are saying then is IF you fool the box into thinking it's got the 19khz in but don't actually put the 19khz on the air, all is good then huh? So use a junk stereo generator in the input of the box and just feed the RDS in like normal, right?
 
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