Operation Settings & Adjustments (FMBM)

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.

Program de-emphasis jumper (JP7)

This jumper sets the de-emphasis curve to either 75µS or 50µS, 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 the Printed Circuit Board Layout and jumper locations image at the end of this article. 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 75µsec position, for European destinations, it is set to the 50µsec position.

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 the Printed Circuit Board Layout and jumper locations image at the end of this article . Set the jumpers as shown on the PCB silkscreen.

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 the Printed Circuit Board Layout and jumper locations image at the end of this article. Set the jumper as shown on the PCB silk-screen. Default position is set to FM.

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.

Pre-emphasis (JP9-JP10)

A Pre-emphasis correction (75 µs) 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.

Peak Integration Time Constant (JP8, JP11)

Select the proper jumper combination (shown on PCB) to select the peak detector’s integration time constant. Possible integration times are 1 ms, 2.5 ms and 5 ms (at 99%).

RF level calibration

RF level adjustment is achieved through the FMBM’s internal menus and built-in voltmeter. This calibration operates in 2 modes, depending on the RF Input that is selected.

Antenna Mode: If you are in Antenna input mode, press the Menu button and scroll down to the Power Monitor Calibration Menu item.

Press Menu again and you will see the current value of the reference level:

Press the Up or Down button and you will see:

Pressing Menu here samples the input signal and sets the new reference level to the currently received signal level and exits the menu item. To exit, simply press the Up or Down buttons to scroll to the Menu mode exit.

High Level Mode: If you are in High-Level input mode, inject a known RF signal into the unit’s RF input, and then press the Menu button and scroll down to the Power Monitor Calibration Menu item.

You should see the following screen:

Press Menu again and you will see:

The voltage shown is the actual voltage present at the FMBM’s back-panel Deviation-monitor output. With a small screwdriver, adjust the “RF Power Monitor Adjust” on the right side of the FMBM’s front-panel to obtain a 5V output that will correspond to the nominal RF Power at the input. The transfer function is 0.5V/dB. Pressing the Menu button again will exit this mode and allow you to scroll back up (or down) to the Menu mode exit.

Printed Circuit Board Layout and jumper locations
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