3M C1060 Manual page 64

475 MHz
These licensed units must compete with other radios of local businesses that may have up to 5
watts of power. However, to maximize battery life, power is restricted to less than 5% of this figure.
This makes them susceptible to interference from these high-powered radios operating nearby.
In addition, there are mobile radios within this frequency range on service trucks, ambulances, and
inventory systems. Therefore, interference is rather unpredictable.
30 and 160 MHz
The lower frequency of these systems is extremely susceptible to interference from CB radios
since they are only about 1 MHz away in frequency. A CB radio in the parking lot or one of the
common, but illegal, radio boosters on a semi on the freeway a mile away can render these systems
unusable for short periods of time. Devastating to a restaurant, and very unpredictable.
Manufactured electrical noises also inhabit the 30MHz spectrum. Fluorescent lights, electric
drills, milkshake machines, light dimmers all cause noises that are picked up on radios operating at
this frequency.
900MHz
The FCC limits the power of all devices operating in this band such that their typical operating
range seldom exceeds 250 feet. A device operating at this frequency seldom can be located close
enough to a restaurant to cause interference. However, when it does occur, our system has 16
frequencies available for instant channel changes.
The largest user in this band is the cordless telephone. Although it can cause interference, a quick
channel change can avoid it. 900MHz phones have begun to use "spread spectrum" technology,
which causes no interference to our system.
Since 900 MHz systems emit about 0.001 Watt of power, they can operate longer on smaller and
lighter batteries.
Few manufactured electrical noises are encountered at these higher frequencies.
Another advantage is the length of a "dead spot". Bouncing radio waves off steel surfaces cause
cancellations of other waves and the net effect is an area where the radio picks up nothing. At 900
MHz the length of this spot is only a few inches versus a few feet for the lower frequency licensed
equipment.
4. Tips and Tricks
• C960 headsets with symptoms of constant "static in the listen mode" are occasionally appearing. If
programming has no effect on the static, these headsets must be returned to the Repair Center to be
"factory programmed". Early tests indicate that dirty battery contacts may be responsible. A
preventive solution is to clean the battery and headset contacts monthly with alcohol and a Q-tip.
• When troubleshooting a C960/C760 base station with intermittent or no power, it is possible to use
the 14VAC power supply supplied with the battery charger and most wired intercoms temporarily.
The base station will work with AC or DC. In fact, some installers have mixed up the charger and
base station supplies. Because of the detrimental effect on the signal to noise ratio, we do not
recommend anything but the proper supply for a permanent installation. Another symptom is that the
batteries don't last very long in the headsets because the base station power supply will not properly
operate the charger.
3