Class A in MONO

[surfdude]

Just interested in what benefits our Class A Oldies station would get broadcasting in Mono - coverage wise.

Tower is centrally located in the market, but a little weak on the fringes and in offices.

Thanks

 

[Turntable]

The 2 main benefits would be:

a) You will be able to modulate slightly higher due to the lack of an FM subcarrier and
b) You will have less multipath problems, especially on the fringes of your coverage area.

Is it worth giving up a stereo signal? That is your call.

-A

 

[gtomas]

If you switch to mono (real mono, meaning killing the 19kHz pilot) you get about 23dB increase in signal to noise ratio, modulation index increases to 5 (versus only 1.5 for stereo) and you significantly reduce multipath problems...


Regards,
Goran Tomas

 

[jboydingram]

I once owned a station with a similar problem, and we went mono...got many complaints because the stereo light would not come on...strange...but true.
The coverage was better, but when the advertisers started to question we
relented and went back stereo...better is not always better, and preception is greater than reality. thanks JBI

 

[gtomas]

Yes, that stereo light is a big issue

Apparently some radios will even skip the stations that don't broadcast 19kHz pilot...


Regards,
Goran tomas

 

[surfdude]

Thanks for the great replies, so far!

Our intention is to leave the stereo pilot on, and strap left and right channels together.
Will we still get any benefit?

 

[Turntable]

Nope. In order to reap any benefits you have to drop the 19khz pilot from your signal. You would have to shut off the stereo gen, resulting in no stereo light.

-A

 

[Leona]

Unless I am wrong, I thought that FM stereo was a supressed carrier, which is why the 19kHz tone is doubled in the receivers to recover the 38kHz carrier? So if the Left and Right inputs are indeed "Strapped" with precise center alignment, if there is no modulation of the stereo subcarrier there should be virtually no subcarrier.

Anyhow, another possibility, and fun experiment might be to ditch the stereo generator and simply insert a 19kHz tone at 9% on top of the mono program audio. This would eliminate any remote possibility of a stereo subcarrier and should still light up the ever popular stereo lights.

I have heard of several Oldies stations operating in mono with no 19kHz tone, and they are very successful stations from what I hear.

 

[ssnake]

Unless I am wrong, I thought that FM stereo was a supressed carrier, which is why the 19kHz tone is doubled in the receivers to recover the 38kHz carrier? So if the Left and Right inputs are indeed "Strapped" with precise center alignment, if there is no modulation of the stereo subcarrier there should be virtually no subcarrier.

Even if you don't modulate the L-R subcarrier, if the pilot is on, the receiver would still be recovering separate channels. This adds noise in low-signal areas (multipath, fringes). Most receivers blend to mono automatically in fringe areas to avoid this.

 

[wgliradio]

Just ask WLNG

They way car stereos blend today, and the poor S/N ratio of portable radios, you may find mono an interesting solution especially if you are in an area prone to multipath problems.

 

[PaulBWalkerJr]

I know the operator of a 100 Watt Class FM NCE in SW Rhode Island that has the stereo light on, but thats it.. no stereo audio.

WLNG rocks!

 

[Turntable]

Paul, that's not the point. The point is that if you simply send monaural audio to the transmitter, with the stereo generator turned on, all you end up with is mono sound on a stereo signal.

Only by turning off the stereo pilot signal at the transmitter/exciter can you keep a stereo radio from turning on its mpx decoder and lighting the stereo indicator. You will still have multipath and mono-mixing problems whether the audio going to the transmitter is stereo or mono.


-A

 

[ISUcyclone]

I actually tested this at the station I last worked at (we were only 250 watts). Not by choice, but because of some problems with the Orban. While we were operating at mono, I noticed coverage definately improved. We got about about two miles further along the interstate and more importantly there was much less noise in the fringe areas. And there wasn't any of that annoying back and forth stereo to mono which can annoy the heck out of many listeners (myself included). The signal sounded perfect even a little below 40 dbu! But we had alot of complaints and once the processor was put back into place we went back to stereo.

Although your program material, mostly being mono to begin with, will sound the same, your paid spots won't. You're advertisers are going to do one of two things (depending on your situatoin): (1) they may notice the "duller" sound of other ads and some may pull their contracts or (2) They will notice the coverage has improved and they will be more willing to buy time.

I suggest you try it sometime for a couple days and see what happens. If you get alot of complaints then just go back to stereo.

Good luck

 

[ironbear]

Mono improves lots of things, but not your relationship with the FCC if you're injecting 19kHZ into a mono transmitter input. In that case, many of the problems (like lower s/n) return anyway, as part of having the stereo demod. circuitry enabled.

 

[jammerdave]

We are running KTKZ-FM in mono, but it's a news/talk simulcast sister to KTKZ-AM. It's a rimshot class B1, and it does make a noticable improvment in fringe area coverage. Lots of stereos these days don't even have stereo pilot indicators, so that's not really an issue, unless you have an analog tuner and use the stereo pilot light as a tuning indicator. (as I used to, back in the day) We have not received one complaint about that. Interestingly enough, we have had many callers to the morning live talk show say how great it is to hear our programming in stereo! They assume being on the FM band means it's stereo...

Go for it!

dave

 

[mikl73]

WYPL 89.3 in Memphis was mono for many years at 2.75kw at 80m i think

not long ago they flipped the switch on to become a C0 and lit up the stereo light
http://www.fcc.gov/fcc-bin/FMTV-service-area?x=FM994601.html

the new stick is located out of the city pretty far and suffers from a little multipath in areas and more so from being mostly talk with low modulated audio often..
the result is pops and hissing as the signal level fluctuates

they should turn it back off in all honesty... it's wierd saying that but its the best scenario for them..

KRNB Majic 101 (now known as KJMS) in the 80s was mono a couple times.. when they were not mono they had the pilot on but it was still mono (seems like they only had a mono STL back then)... I remember them on the aux/back up located at the studio and hearing them go from mono carts to stereo vinyl and I think you could hear the tones on the carts on the air also..
Catching them on the Aux was the only time you would hear music in stereo but then you had to tolerate the buzz caused by RF since the Aux TX was only a few feet away.

My only advise is make sure with oldies you do get a sum of L & R and that nothing is out of phase. Beatles records will tell you you every time.

 

[mikl73]

Most receivers blend to mono automatically in fringe areas to avoid this.
[/quote]

I never could figure out why they wouldn't put a hold or delay on car radios that do this or that reduce the high end.. I find it quite annoying being in a stations fringe and the Radio is fluttering from mono back to stereo constantly or its dropping the high end in and out attempt in hiding the hiss of the weak signal.. this a not a terrible feature as I actually have it enabled on my Blaupunkt LOS Angeles MP72. It would be nice if there was a delay on some radios when the signal momentarily rises above the threashold to prevent it from going back and forth. I'm fortunate that my Blaupunkt does flutter like many radios do when they have this feature.

 

[radiorob2.0]

Another famous mono station is WSGS Hazard, Kentucky. Many time through the years they have attempted stereo but the multipath through the mountains destroyed the signal so they revert to mono. It's ironic but at one time the two AM station licensed to Hazard were stereo while WSGS-FM was mono.

 

[oldrover]

How would one test this on an existing station to determine the benefit? Switch to mono and perform field tests? I'm looking at a class A FM switch to news/talk/sports, and the switch might enable the station to pick up additional sellable towns.

 

[rfry]

How would one test this on an existing station to determine the benefit? Switch to mono and perform field tests?

The specifics will vary depending on your equipment lineup is, but in general you will need to take a mono output from your audio console, transport it to the mono input of your FM exciter, and (of course), remove/disable your FM stereo generator. Your mono modulation level should be checked and re-set to a legal peak.

Your "field tests" should not be expected to show much (if any) difference in received signal strength anywhere. The differences that exist will be in the noise and distortion level of the mono signal at the receiver output, other things equal.
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