Portable and mobile radios contain a crystal oscillator to keep them on frequency, but these reference oscillators tend to drift over time. These crystals are directly impacted by the voltages applied to them which make them resonate. These controlling voltages are affected by aging of electronics, battery power, temperature, environment, and mounting conditions. The effect of these variables can be seen in the drift or detuning of oscillators which in turn degrade the signal of a land mobile radio.
To correct for these variables, within limits, some radio manufacturers have built in a technology that enables the radio to adjust frequency misalignment or frequency error. This is a temporary correction known as Automatic Frequency Control (AFC) or Automatic Fine Tuning (AFT). If you are not aware of the AFC technology embedded by your vendor, then you might have a false sense of security regarding the performance of your radio system.
Although AFC helps communication devices continue to work, it only temporarily controls and corrects the oscillator drift, masking a hidden problem until the radio fails. AFC is applied in progressive steps until the target alignment is reached, but the correction goes away when the radio is turned off. A poorly aligned radio often requires multiple attempts to affiliate with the network before AFC engages, unnecessarily taxing the system. A radio like this, even while temporarily appearing to be within spec, should be brought in for maintenance. As the radio continues to drift further out of alignment AFC will no longer engage resulting in a hard failure.
Software corrections, like AFC, are a helpful feature in the short term; however, radios still need to be properly aligned to continue working long term. LocusUSA has developed a patented technology to determine how much AFC correction is being applied to a subscriber radio in real time while deployed in the field. The DiagnostX AFC Meter measures the temporary AFC adjustment by capturing and analyzing all control channel transmissions from the radio. The DiagnostX AFC Meter is an add-on feature to the DiagnostX systems.
