Fisher 1212-X - False Signals

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Due to the sensitivity of the 1212-X, you’re bound to get some “false
signals” once in awhile. A false signal occurs when something that
shouldn’t sounds like a good target. The 1212-X does a good job
of rejecting junk but it can be fooled by “hot” mineralized spots
in the soil, large pieces of junk, some kinds of bottle caps and pull
tabs or trash less than 2 inches from the coil.
So what do you do about false signals? Well, 90 percent of them
will sound suspicious to you after you’ve had some experience and
you’ll just ignore them. They may be very faint or very abrupt with
static. Often when you go back over the same spot, a false signal
will simply disappear. Other false signals may be very loud and
sharp but most of these will also disappear if the coil is speeded up
or raised slightly. Some shallow, or large or irregular pieces of junk
however, will sound off no matter what you do. You may reduce
the number of false signals by increasing the trash rejection level.
Some other sources of false signals are:
1. ELECTRICAL INTERFERENCE: Caused by radio/TV
stations, power lines, or nearby detectors operating
at the same frequency.
SOLUTIONS: Move further away, reduce sweep
speed.
2. HIGHLY MINERALIZED SOIL: Usually causes constant
static on good target sounds. SOLUTIONS: Increase
trash rejection level, raise the search coil until false
signals disappear and sweep at that height.
3. WET SAND: Same as highly mineralized soil.
4. ELONGATED FERROUS OBJECTS: If you hear two
beeps very close together and can’t find either one,
you’re probably over a nail (see Figure 4) or some
other long iron object. But a very shallow coin or a
buried coin on edge may give the same response. In
all cases, the target will be between the beeps or, if
you sweep at right angles to your original direction,
you’ll receive a single beep directly over the target
(except for the very shallow coin). One way to tell
the difference between a coin and a nail is to set
your trash rejection to about 5. Most small nails will
be tuned out while most coins will respond with a
good, smooth signal.
FALSE SIGNALS