[BC] Running mono on FM...

[Robert Orban]

At 07:58 AM 1/17/2006, you wrote:
>rom: "Andy Green \(Listservers\)" <andyglist at totalbroadcast.net>
>Subject: Re: [BC] Running mono on FM...
>To: "Broadcasters' Mailing List" <broadcast at radiolists.net>
>Message-ID: <01ce01c61b65$9bd0d840$9a02a8c0 at Accounts>
>Content-Type: text/plain; format=flowed; charset="iso-8859-1";
>         reply-type=response
>
>
>----- Original Message -----
>From: "Burt I. Weiner" <biwa at earthlink.net>
>To: <broadcast at radiolists.net>
>Sent: Tuesday, January 17, 2006 6:33 AM
>Subject: [BC] Running mono on FM...
>
>
> >   Just a word of caution - if you simply turn off the pilot be sure you
> > are not leaving the L-R channel running.  One L.A. station was leaving the
> > L-R on and only feeding mono to the left channel.  The L-R channel was
> > gobbling up modulation.
> >
> > Burt
>
>I don't think this is the case (I seem to recall this being discussed before
>on this list) - Bob Orban or someone else good with the Math may care to
>comment, but correct me of I'm wrong, the major downside to broadcating in
>Stereo is the increased signal to noise ratio that comes with demodulating
>the L-r info - since the noise level increases with frequency in FM the
>penalty is quite high.

If one broadcasts "mono" by turning off the pilot tone while sending 
program to one stereo channel and silence to the other, you will lose 6 dB 
of loudness in the L+R channel, which is what receivers will pick up in the 
absence of a pilot tone. It is crucial to remove modulation from the stereo 
subchannnel.

All Optimods have "mono from left channel" and "mono from right channel" 
modes that mute the stereo subchannel and pilot tone and make appropriate 
gain adjustments to ensure that the carrier continues to modulate +/- 75 
kHz. More recent Optimods have a "mono from L+R" in addition to the other two.

These modes can be triggered locally from the front panel, via GPI contract 
closures, and (in recent Optimods) by time-of-day automation.

Bob Orban