Youtube Reference; Threshold B Null Position; Small Search Coils - QED PL3 Owner's Manual

2. THRESHOLD B – (THS-B) (BIAS)

YouTube Reference

Threshold B NULL Position

YouTube Reference

Small Search Coils

Tip:
Use a test target of say
0.2g. If the 0.2g is louder
and more noticeable
after lowering THS-B,
then BIAS has been
achieved for better
detection on smaller
targets
Tip:
When searching for
small targets: use a
small coil, a volume of
~30 or less, a gain of ~4,
with the THS-B set
below NULL until a
slight threshold is
created.
Click on this YouTube link
When looking for both rising and falling pitch targets it's best to put
THRESHOLD B in the NULL position (around 50) and raise
THRESHOLD A to create your desired threshold level.
Locating the "NULL Position" is determined by raising and lowering
Threshold B and taking note of the numbers as per the following
procedure:
Start by raising THRESHOLD B with the
•
THRESHOLD B starts to get to a tolerable volume level (e.g.
58).
Then lower THRESHOLD B with the
•
the same volume level e.g. 44.
The above example range is 58 less 44 = 14.
o
Halve the 14, which becomes 7.
o
Add 7 to 44 = 51.
o
51 is then the THRESHOLD B NULL position in this example.
Click on this YouTube link
When using small coils for small (tiny) targets, set the THS-B to an
acceptable audio level below the NULL position.
From the NULL position, decrease THRESHOLD B with the
button until an acceptable threshold volume is created (i.e. not too
noisy)
This will boost target responses for smaller targets in the ground.
Process:
• If a small coil is fitted, test the THS-B out with a small target.
• Swinging the coil over it will produce a rising pitch response.
• Lower the THS-B by one count at a time and note the
improvement in detection distance.
• Keep lowering THS-B until the background audio is at an
acceptable level.
Note: If THS-A is high then just a change of 1 or 2 on the BIAS will make the
QED too sensitive/unstable.
19
to see how to set Threshold B.
to see how to set Threshold B to NULL
Setting range 1-99
Factory preset at 50
button until the
button until you get