[BC] Stereo Pilot question...

[Burt I. Weiner]

If you look at the dB scale on your modulation monitor, you will see 
that at 10% injection, the pilot only takes about 1 dB of the 
modulation.  Moving it down a couple of tenths in injection level is 
only a very small fraction of a dB in modulation.  Who could possibly 
notice the difference?

The real culprit is the L-R channel.  In a weak signal condition the 
L-R channel, which is located between 23 and 53 kHz out from the 
carrier, will noise up before the main channel.  The stereo decoder 
will mix this noise into the audio.  This is why more modern stereo 
receivers blend to mono.

Dropping the pilot will turn off the stereo decoder in the receiver's 
decoder and eliminate the L-R channel from contributing to the noise 
and the perceived weak signal caused by the noise in the L-R 
region.  Turning the pilot down to the lower legal limit (or even 
lower) will only cause the receiver to drop back to mono 
earlier.  Depending on the receiver, this could be more annoying than 
the noise in the L-R channel.

There are three issues you need to be concerned with in dropping the 
pilot and going mono:

1. Will your audience complain, care or even notice?

2. In the olden days there were car receivers that would not lock on 
a station that did not have a pilot.  I doubt there are any of these 
receivers still around.

3. If you have RDS you may need to supply a 19 kHz signal to the 
synch spigot on the RDS generator.  Most that I've seen don't require 
it.  Your's may be different.  If it mutes when you remove the pilot, 
find an old stereo generator just to supply the pilot for the synch 
spigot.  I don't know if the receiver requires a pilot in order for 
the RDS decoder to work.  I don't think it does.

3-1/2.  In dropping the pilot you will be forcing all receivers to 
hear the summed (L+R) channel.  If you have any audio phase shift 
issues they will show up.  If seen several stations that have issues, 
but due to running stereo, and very few receivers are mono, the 
problem is not as obvious.  This holds true when receivers blend to 
mono.  It's hard to imagine a station having a problem in this day 
and age unless something is wired wrong.

Bottom line:  Try it - it's not a Heart-Lung machine.  The switch 
works in both directions (unless it's a really old switch).

Burt

At 06:00 AM 2/28/2010, broadcast-request at radiolists.net wrote
>Chuck,
>
>Nothing wrong with experimenting with mono only; it certainly won't 
>hurt anything. If your signal is getting noisy, then you don't have 
>enough RF to go around. Increasing modulation density is not going 
>to help much.
>
>Playing with the stereo pilot is false economy. Dropping the pilot 
>level will reduce your stereo coverage. Sure, reducing the pilot 
>will in theory, make room for more program modulation, but the 
>stereo receivers will lose stereo lock sooner, the more you reduce 
>the pilot injection. It might not matter much in your case since you 
>are already considering going mono.
>
>It sounds to me like the biggest you're having has more to do with 
>RF coverage. You might want to consider having the antenna checked 
>out to verify that you're getting all the coverage you can. Check 
>the orientation of the antenna on the tower.
>
>I don't think you will be able to make the noisy signal sound clean 
>by doing anything with modulation levels. The exception is if your 
>modulation is much lower than it should be. Check this by listening 
>to your station in a strong signal area and compare your loudness to 
>other stations. You have a modulation density problem if you are 
>tempted to turn the volume up on your radio when tuning from the 
>other signals over to your own station. Grossly weak modulation will 
>make the signal sound hissy. Don't get carried away with using 
>processing to extend your coverage. This is an option but it is 
>limited in effectiveness. You can't use modulation density to take 
>the place of a weak RF signal.
>
>It's always a good investment to have a state of the art audio 
>processor in your system; it's to your advantage to get the most out 
>of your signal. If your philosophy is to provide the loudest signal 
>or the cleanest signal, you must have a good audio processor to do 
>that. This is true for either a stereo station, or a mono station.
>
>Best of luck and do let us know what you come up with.
>
>Jeff Glass