The newer F75's now come with the following sheet explaining more about so-called "interference". Those of us who bought the first F75's, or those doing possible research on a purchase may find the following helpful......
There are no electrical interference problems with the detector. What actually happens is the F75 is so sensitive that the sensitivity
setting must be adjusted given it surroundings.
ELECTRICAL INTERFERENCE
The Fisher F75 is probably the most sensitive metal detector ever
manufactured.
Such high sensitivity makes the F75 susceptible to electrical
interference. In Discrimination
Mode, electrical interference may cause the F75 to chatter or beep
spontaneously. Indoor use, or use in proximity to buried or overhead power
lines, will result in chatter at high sensitivity settings.
To overcome chatter, which is usually due to electrical interference,
you can:
1. Try sweeping it over the ground.
If the F75 chatters while held still, or held up in the air, it
may be much quieter
when sweeping over the ground.
or 2. REDUCE the SENSITIVITY.
At a reduced sensitivity level, the F75 will still give good
detection depth.
Reduce sensitivity until the chatter stops. This may be a very low
setting.
or 3. Search in an All-Metal Mode.
Interference is much more tolerable in these modes, even at high
sensitivity.
SENSITIVITY FEATURES
Sensitivity settings from 1 to 29 have the following characteristics:
In an All-Metal Mode, you may notice more background noise than
at higher (30-99) settings.
The F75 will be more resistant to overloading on large targets
or salt water at settings of 1-29.
You may find that sensitivity increases as you increase the
discrimination level.
This behavior is normal for the F75. If increased discrimination
results in chatter,
then reduce the Sensitivity Setting.
BATTERIES
You may experience "chatter" or erratic behavior if using
inferior batteries, or discharged batteries.
If the lowest battery bar flashes, replace the batteries.
If all battery bars disappear, replace the batteries.
Use only battery types as recommended on page 6 of the manual.
Do not use ordinary zinc-carbon batteries.
There are no electrical interference problems with the detector. What actually happens is the F75 is so sensitive that the sensitivity
setting must be adjusted given it surroundings.
ELECTRICAL INTERFERENCE
The Fisher F75 is probably the most sensitive metal detector ever
manufactured.
Such high sensitivity makes the F75 susceptible to electrical
interference. In Discrimination
Mode, electrical interference may cause the F75 to chatter or beep
spontaneously. Indoor use, or use in proximity to buried or overhead power
lines, will result in chatter at high sensitivity settings.
To overcome chatter, which is usually due to electrical interference,
you can:
1. Try sweeping it over the ground.
If the F75 chatters while held still, or held up in the air, it
may be much quieter
when sweeping over the ground.
or 2. REDUCE the SENSITIVITY.
At a reduced sensitivity level, the F75 will still give good
detection depth.
Reduce sensitivity until the chatter stops. This may be a very low
setting.
or 3. Search in an All-Metal Mode.
Interference is much more tolerable in these modes, even at high
sensitivity.
SENSITIVITY FEATURES
Sensitivity settings from 1 to 29 have the following characteristics:
In an All-Metal Mode, you may notice more background noise than
at higher (30-99) settings.
The F75 will be more resistant to overloading on large targets
or salt water at settings of 1-29.
You may find that sensitivity increases as you increase the
discrimination level.
This behavior is normal for the F75. If increased discrimination
results in chatter,
then reduce the Sensitivity Setting.
BATTERIES
You may experience "chatter" or erratic behavior if using
inferior batteries, or discharged batteries.
If the lowest battery bar flashes, replace the batteries.
If all battery bars disappear, replace the batteries.
Use only battery types as recommended on page 6 of the manual.
Do not use ordinary zinc-carbon batteries.
