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Davicom FMBM, Reference Manual, March 2015
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4.4 Settings & adjustments
The FMBM has 9 internal jumpers, one RF alignment, one RF level calibration and one MPX
level adjustment that allow users to optimize operation of the unit for their particular
requirements. No other user adjustments are required for normal operation.
4.4.1 Program de-emphasis jumper (JP7)
This jumper sets the de-emphasis curve to either 75
S or 50
S, depending on the region of
the world where the FMBM is being used. This jumper is located near the 12Vdc XLR Power
connector as shown at the top right of Figure 20. Set the jumper for the desired de-emphasis
curve as indicated on the PCB silk screen. For deliveries in North America, the jumper is set
to the 75
sec position, for European destinations, it is set to the 50
sec position.
4.4.2 Relay mode selection jumpers (JP2-JP6)
These 5 jumpers set the default connection mode of the alarm relay outputs. They can each
be individually set to Normally Open (NO) or Normally Closed (NC).
The 5 jumpers are
located as shown at the bottom right of Figure 20. Set the jumpers as shown on the PCB silk-
screen.
4.4.3 Power monitor filter jumper (for AM mode, JP1)
The Power Monitor filter jumper adds extra filtering to the detected signal envelope in order to
smooth out variations when in AM mode.
This helps to improve the RF Power detection
readings when operating on the AM band. This jumper’s location is shown at the bottom left
of Figure 20. Set the jumper as shown on the PCB silk-screen. Default position is set to FM.
4.4.4 RF alignment
RF Alignment is not necessary for normal operation of the FMBM unit.
Depending on
antenna type and matching, RF alignment does however allow fine tuning of the RF input
circuit in order to optimize signal reception in weak-signal areas.
RF Alignment is achieved through the front-panel menu and buttons. Press the Menu button
and then scroll down to the RF Alignment menu item by pressing the Down button. Selecting
this Menu item displays a tuning setting between 0 and 127, as well as an RSSI level in dBm.
Press the up or down buttons to change the tuning setting in order to maximize the receive
signal level. Once the highest signal is achieved, store the setting and simultaneously exit the
RF Alignment mode by pressing the Menu button again.
4.4.5 Pre-emphasis (JP9-JP10)
A Pre-emphasis correction (75
s) will be applied to the audio output signals when jumpers
JP9 and JP7 are installed. The correction is applied to the analog output as well as the digital
output when the FM-AES option is installed.
