Wireless Tips

There is an important feature found in all FM communications and wireless mic receivers that relatively few users appreciate or are even aware of at all. Its job is to keep the receiver quiet when it is on but not receiving a signal. Without it we would hear continuous ”white” noise at full level and risk damaging speakers or even ears, not to mention ones mental condition.

We are referring to the lowly squelch circuit. In its most basic form it is a noise gate that simply blocks the receiver’s audio output the instant the transmitter is switched off or the signal is lost owing to a dropout or extreme range. In its most sophisticated form, Tone-Key Squelch, as used in all of Shure’s current UHF systems, offers some very useful additional benefits.

Many wireless users find it desirable to leave their permanently installed receivers on 24/7 and often into a powered-up PA system. This practice is especially common in houses of worship. The ability to simply turn on the transmitter rather than having to go to the receivers, throw a series of switches, move faders or even call a tech to be “on” is extremely convenient. The very low power requirement of modern electronics makes it entirely practical to but there is a risk. A risk, that is, when using a receiver with a conventional “carrier” squelch circuit. As the receiver sits powered on day after day “looking for a signal” it is only a matter of time until stray RF causes a blast of noise through the system. It will most likely be caused by something operating primarily on an entirely different frequency that throws off spurious signals on various other frequencies and one or a combination of them hitting a receiver is inevitable.

Tone-Key Squelch to the rescue! Rather than depend on the simple detection of an RF signal or carrier to cause the receiver to open its squelch and pass audio, a Tone-Key equipped receiver looks for a 32.768 KHz. tone that all matching Shure transmitters send out along with the carrier. We can’t hear it but the receiver knows when it’s there and when the stray signals hit without the tone the resulting noise will not be passed on into the PA system and it will remain secure.

This single benefit alone would justify a Tone-Key system but there are two others of almost equal importance. Anyone who has used a conventional wireless system has at some point switched a transmitter off with the PA system “hot” and experienced the mega-pop that can result. A Tone-Key equipped system will not do this because the transmitter will turn off the tone a second before the power thus muting the receiver and preventing the pop from getting out. This is definitely an embarrassment saver and possibly a speaker saver too.

The third benefit is in battery power monitoring. Most wireless transmitters on the market have an LED or some sort “fuel gauge” to tell the user when the batteries life is coming to an end. However, the benefit of having that information displayed on the receiver can be readily appreciated. After all, the talent is not likely to tell the tech that the battery needs changing. The tone is easily capable of carrying this information in as much as five-segment resolution so the receiver can display it on its LCD.