Setting Up the Hardware

• 1: Connecting the NMR Probe
• 2: Connecting an External Amplifier
• 3: External Trigger

System Description

Front Panel Connectors

The NMR probe is connected to the Bridge12 SCN using the SMA connector located on the front panel of the system.

Back Panel Connectors

Most connections for the Bridge12 SCN are located on the back panel.

Connector Label	Style	Description
USB	USB-B	USB connection to spectrometer computer
PWR	Circular	System power connection. The input voltage for the system is 24 VDC, 1.25 A. To power the system, please use the power (desktop) adapter that was delivered with the system.
FILT IN FILT OUT	SMA(f)	Receiver input filter (bandpass). The bandpass filter is used to reduce the noise in the system. By default the Bridge12 SCN comes with a bandpass filter for 1H NMR spectroscopy. If you like to operate the system at a different Larmor frequency the filter has to be replaced with a bandpass filter for the desired frequency. Additional filters can be found on the MiniCircuits webpage.
λ/4	SMA(f)	Connection for the λ/4 cable. The Bridge12 SCN uses a passive Transmit/Receive (T/R) switch to protect the receiver. For this an appropriate λ/4 needs to be conneted to the two connectors. By default the system comes with a λ/4 cable for 1H NMR spectroscopy. If you wish to study other nuclei you need to replace the 1H with a cable with a different length. Instructions to make your own cable can be found on the webpage for the OpenTRSwitch or contact Bridge12 at support@bridge12.com.
AMP IN	SMA(f)	External amplifier input.
AMP OUT	SMA(f)	External amplifier output.
AMP BLNK	SMA(f)	Blanking gate for external amplifier. The blanking gate is active low. If you have questions about how to connect an external amplifier please contact Bridge12 at support@bridge12.com
MPS TRIG	SMA(f)	Trigger pulse for the Bridge12 MPS to modulate the output power. The trigger is active high.
SP	SMA(f)	Not used.
TRIG/STAT	D-Sub (f)	Auxiliary connector. Pinout: 1: 10 MHz reference for external use, 2, 3: Not connected, 4: Hardware trigger, 5: Hardware reset, 6, 7, 8, 9: GND

SMA(f) - Female SMA connector

Fuse

A fuse holder is located on the back panel of the SCN. If necessary, the user can replace the fuse. The dimensions are 5x20mm and the fuse should have a rating of 1.25A.

Placing the System

• Place the Bridge12 SCN close to the EPR spectrometer. It is recommended to keep the length of the cable connecting the probe to the system at a minimum length.
• The system should rest on a stable surface.

TRIG/STAT Channel Explanations

• 1 - 10 MHz Reference:
  • The 10 MHz reference is the master oscillator output
• 4 - Hardware Trigger:
  • When this is pulled to GND an acquisition resumes or starts
• 5 - Hardware Reset:
  • When this is pulled to GND the pulse program is reset - as long as this is low no pulses are generated and sent out
• 6/7/8/9 - Ground

Connecting the System

Electrical Connections

To power the SCN connect the external power supply to the PWR connection. then connect the USB-C port to a PC. Connect the input of a bandpass filter corresponding to your NMR frequency to the ‘FILT OUT’ connector and the output of the bandpass filter to the ‘FILT IN’ connector. Connect a \(\lambda\)/4 filter (e.g. a cable with the correct length) for your NMR frequency to the \(\lambda\)/4 connectors.

Connecting the NMR Probe Circuit

Changing the RF Filters

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1 - Connecting the NMR Probe

The connector to connect the NMR probe to the Bridge12 SCN spectrometer is located on the front panel. The input impedance is 50 Ω.

If your probe has a BNC connector please use a SMA-BNC Adpater and a BNC cable to connect the probe.

2 - Connecting an External Amplifier

The Bridge12 SCN has an internal RF power delivering up to 2 W output power. For many (low frequency) experiments this power is sufficient.

If the available power from the internal amplifier is not sufficient, an external high-power RF amplifier can be connected to the system.

To connect an external amplifier the input of the external device must be connected to the AMP OUT connection on the back panel of the SCN. The output of the external amplifier must be connected to the AMP IN connection located on the back panel.

To blank the external amplifier, connect the blanking gate to the AMP BLNK output of the SCN. The blanking gate is active low.

Specifying the Amplifier pre-Blanking Time rof1

To use an external amplifier with blanking, the amplifier needs to be unblanked before sending the RF pulse. Amplifiers typically require a short time unblank. This time can be specified using the OVJ parameter rof1. The value is typically given by the manufacturer in the data sheet of the amplifier.

The value can be set from the OVJ command line:

1

rof1=1000

If the required value is larger than the default value, for rof1 can be changed using the setlimit command as shown below.

1

setlimit('rof1',MAX_VALUE,MIN_VALUE,STEP)

Enabling the External Amplifier and Setting the Drive Level

OVJ needs to be connected to use the external amplifier. This is done from the OVJ command line:

1

B12SCNControl('extamp 1')

The B12SCNControl('state?) command can be used to query the state of the amplifier. If the system returns “extamp” the external amplifier is enabled.

1

B12SCNControl('state?')

The drive level (input power) of the external amplifier can be set using the OVJ command line by specifying the value stored by tpwrf.

1

tpwrf=1

To disable the internal amplifier from the OVJ command line enter this command:

1
2

B12SCNControl('extamp 0')
B12SCNControl('state?')

If the command B12SCNControl('state?) returns “intamp”, the internal amplifier is used. The tpwrf value is automatically set to 100 (the maximum).

3 - External Trigger

The acquisition of an NMR spectrum by the Bridge12 SCN system can be triggered using an external trigger. The external trigger is connected to the TRIG/STAT connector located on the back panel. The pinout for the connector is given in the section describing the Back Panel Connectors.

The trigger is active low on the falling edge. This means, pulling pin 7 on the TRIG/STAT connector to GND will start the acquisition of an NMR spectrum. By default every acquisition needs to be triggered. If you require a different behavior (e.g. trigger 4 acquisitions to complete a phase cycle) the pulse program need to be changed accordingly. For further information please contact Bridge12 at support@bridge12.com.

The system also has a hardware reset, accessible through pin 9 on the TRIG/STAT back panel connector. When this pin is pulled to GND, the pulse program will reset. As long as the hardware reset of the SCN (pin 9) is pulled to GND no RF pulses are generated and send to the amplifier. Acquisition of an NMR spectrum is not possible.

Enabling the External Trigger

The external trigger needs to be enabled in OVJ for the user to be used. This is done either:

1. from the OVJ command line:

   1	B12HWTriggerFlag=1

2. by setting the value in the Enable HW Trigger (in the Acquisition tab) to 1

3. or by activating the HW Trigger checkbox in the 1H tab

Disabling the External Trigger

To disable the external trigger use the command

1

B12HWTriggerFlag=0

or set the value in the Enable HW Trigger box to 0 (Acquisition tab) or disable the checkbox in the Default 1H tab.