Instruction manual
84Understanding your X-TERRA - Technology
Q
A
For many metal detectors, implementing Noise Cancel is
typically a slight shift in operating frequency. If the Noise
Cancel process of the X-TERRA is similar, how much of a
frequency shift does each channel of Noise Cancel represent?
It should be noted that operating on a frequency dierent from the resonance
of the coil introduces a phase angle shift, but VFLEX technology accurately
compensates for this and neither Ground Balance nor TID are aected.
Q & A with Laurence
Similar to other metal detectors, the Noise Cancel in X-TERRA
changes the operating frequency of the detector by a small
amount around the resonant frequency of the coil. This
precludes narrow band interfering signals from aecting
the operation of the detector. Because X-TERRA uses pure
sine waves for demodulation, the interference must be very
close to the operating frequency to be a problem. Of course,
broadband interference (like that from car ignition, electric
welding or thunderstorms) cannot be cured with Noise
Cancel, but in this case the very sharp and deep attenuation
of the digital lters helps minimize the eects.
The number of steps (3 or 5) for Noise Cancel depends on the model of detector,
with frequency 0 being always the resonant frequency of the coil, as recorded
in the coils microcontroller during the calibration at the factory. The steps in
frequency depend on the coil frequency, with LF coils having smaller steps and HF
coils having the largest steps:
• LF Noise Cancel frequency step: 35 Hz
• MF Noise Cancel frequency step: 40 Hz
• HF Noise Cancel frequency step: 80 Hz
Noise Cancel Channel
Detector
X-TERRA 305
X-TERRA 505
X-TERRA 705
Coil freq. -2 -1 0 1 2
7.5 kHz
18.75 kHz
7.5 kHz
18.75 kHz
7.5 kHz
18.75 kHz
3 kHz
7.420 kHz 7.460 kHz 7.500 kHz 7.540 kHz 7.580 kHz
18.590 kHz 18.670 kHz 18.750 kHz 18.830 kHz 18.910 kHz
2.930 kHz 2.965 kHz 3.000 kHz 3.035 kHz 3.070 kHz
3 kHz
7.420 kHz 7.460 kHz 7.500 kHz 7.540 kHz 7.580 kHz
18.590 kHz 18.670 kHz 18.750 kHz 18.830 kHz 18.910 kHz
2.930 kHz 2.965 kHz 3.000 kHz 3.035 kHz 3.070 kHz
7.420 kHz 7.460 kHz 7.500 kHz 7.540 kHz 7.580 kHz
18.590 kHz 18.670 kHz 18.750 kHz 18.830 kHz 18.910 kHz