radio station broadcasting silence

If a radio station was to broadcast silence, would we hear it as silence or static? Is there really any difference between broadcasting silence and not broadcasting at all?

If you’re listening to talk radio, and the host adds a dramatic pause to his speaking, does it suddenly burst into static? Or do you hear silence? Why would that change if he didn’t say anything for a LONG time?

That’s basically the root of my question. Since we don’t get static in those cases, there must be some technical difference between not broadcasting and broadcasting silence. But how does that work? If I had a strong enough station could I simply broadcast silence and no-one would hear anything?

When there is no transmission from a radio station, your radio will be picking up the random radio noise of the universe that happens to be at that frequency. What you hear is the average amplitudes being picked up at that frequency.

But when there’s a definite man-made signal, it’s strength overpowers the random radio noise. The average signal received at a given frequency of a station is almost exactly the same as the station’s original broadcast. The radio program is what’s basically played out on the speaker.

If that station is broadcasing silence (break between commercials, pauses in conversation, etc.), that low amplitude signal is bringing down the average amplitude received at your radio. If you listen closely during silences (with the volume up), you’ll hear the random static, just greatly reduced.

But what if they were broadcasting subliminal messages at really high frequencies (to attract dogs and other animals to their station)?

Wait… they can’t do that… at least not with AM radio, since the frequency is constant there. Or is there a difference between the frequency of the signal and the frequency of the sound it produces? Otherwise you’d only get monotone radio…

[unrelated rant]My sports-talk radio station has some weird satellite interfernce/connection problem to the station that originates the Papa Joe Chevallier show. Every couple of minutes the show will just stop, right in the middle of a sentence, and go completely silent for a few seconds. Then it will come back, and I will have missed on of Papa Joe’s profundities. Drives me freaking nuts! [/unrelated rant]

It gets quite deep when you think about it. A two-dimensional radio wave (frequency and amplitude) carries with it more information: sound frequency.

Basically, the rate that the amplitude is changing is what is reproduced at the speaker. The quicker it changes, the higher the pitch heard.

When a complex signal, with sound, singing, sound effects, etc., is broadcast, the amplitude jumps and “vibrates” very erratically, but when applied to a speaker, makes sound that our brains interpret. Pretty @!#?@! amazing!

Let’s see if I can remember any of my broadcast engineering.

Both AM and FM radio stations use carrier waves for their signal. Even if they aren’t broadcasting anything at that moment (silence) the carrier waves are still being sent, so rather than picking up static (random radio noise of the universe – what a nice phrase!) your receiver is still locked on the station. Which means, it’s receiving silence.

And back in my radio days, the rule was you couldn’t broadcast silence for more than 2 minutes, or else you had to cut the carrier. It went back to not cluttering up the air waves.

This thread brings back a memory of my days on the air on a rock station.

Well I was new and wasn’t that good with the board yet. And happen to notice my headphones were on audition instead of on program.

Well I thought I was playing the song over the air when in fact I was playing nothing. But being quick on feet I came back on the air saying, "that was “Silience, an obscure Led Zepplin tract that hardly anyone ever plays and you heard in first on this station…” :smiley:

Yes, although it’s more apparent with FM signals than with AM (mediumwave).

Having the transmitter operate without transmitting any audio is referred to as “dead air” or an “open carrier”. And doing this does tend to drown out static or any other stations which happen to be operating on the same frequency.

With FM signals, the “capture effect” makes this even more effective. For FM signals, radio receivers will “lock on” to signals if they about twice as stong as a second signal on the same frequency. It doesn’t matter if the stronger station is broadcasting any audio or not–if it is the stronger signal, then when you turn to its frequency all you will hear is silence. (If you have two distant FM stations about the same strength, then by moving the antenna around you will often switch abruptly from hearing one station and then another, as the capture effect favorings one station or the other, depending on the orientation of the antenna).

On AM (mediumwave) there is no capture effect, so the sounds of mutiple stations operating on the same frequencies will be audible simultaneously. (This is more apparent at night, when mediumwave signals travel much farther.) However, a nearby station operating with an open carrier does muffle the signals of any other stations on the same frequency.

Here in the United States, some mediumwave stations operate only during the daytime. Many times I have heard a station give its sign-off message, then pause for a few seconds before turning off the transmitter. Depending on how close the station is, during the period until its transmitter shuts down, you can often hear other weak stations, which suddenly become much stronger when the local transmitter shuts down.

In a more extreme case, I live about 1 kilometer from a 50,000 watt mediumwave transmitter that operates on 680 kilohertz. Its signal is so strong that even during pauses in their programming I never hear any of the other stations in the U.S. that operate on this same frequency, although they would be faintly audible if the station signed off.