Getting to Know Lab Brick Part Two: Signal Generators

Posted on Wednesday, January 21, 2015
By Scott Blanchard

As instruments rather than components like attenuators and phase shifters, signal generators are obviously more complex, and our goal has been to make the Lab Brick LSG and LMS Series instruments easy to use but very capable.


As you can see from the figure below, frequency, frequency and power step size, as well as pulse and sweep modes are all configured in the same screen. The frequency-setting field is on the left and you just type in your desired frequency into the window and hit the computer’s “Enter” key. The PLL indicator in the window will turn green to verify that the frequency is established. You can also use the up/down arrows.


Below this is where you set the desired step size and we give you some presets: 100 kHz and 1, 10, and 100 MHz. Select “Other” and you can enter any step size between 100 Hz and 1000 MHz. The signal generators can be configured to linearly sweep through a range of frequencies, and setting this up is simple. Enter the start and end frequencies and sweep time. You can’t make a mistake because minimum start and end frequency limits are specific to the Lab Brick signal generator you’re using. The sweep time can be set from 1 ms to 1000 s.


The software will sweep once if you select “One Time” and “Stop” disables the sweep. Select “Repeat” and the signal generator will repeatedly sweep from the start to end frequency, blank the retrace, and begin the sweep again at the start frequency. You can also perform a “bidirectional sweep” by checking the box enabling this function. In a bidirectional sweep the signal generator sweeps from the start frequency to the end frequency and back again. Sweep time is the time is takes to go from start to stop frequencies so the full cycle from the start frequency back to the start frequency is twice the specified sweep time.


On the same screen, you also set the RF output power by typing the desired output power into the window or via the up/down arrows as shown below. Next to this on the screen is the step size, so once again have presets: 1 and 10 dB. Select “Other” and you can choose any step size between 0.5 and 40 dB in 0.5-dB increments.


After setting frequency and power, you can save the current settings in the device from the File menu at the top of the screen, so the next time you power-up the signal generator this state will be recalled.


One of the useful functions in our software is the ability to allow the Lab Brick generators to operate from a USB power source (a USB hub) even if they’re not connected to a computer. Once you’ve configured the generator and saved the setting, remove the power by unplugging the instrument from the USB hub. When power is again applied whether from USB hub or USB battery pack the instrument will operate at the saved setting.


There may be times when you’ll want to synchronize the Lab Brick from an external 10-MHz clock reference. To do that, connect the source to the BNC connectors on the instruments and select External Reference from the Control menu. The display will show a check mark next to External Reference command. You can also toggle between reference sources using the F3 key on the keyboard.


The Lab Brick instruments can generate pulse modulation, which you enable and configure from Pulse Mode, which lets you control pulse width and pulse repetition interval. The minimum pulse width is 100 ns and minimum pulse repetition rate is equal to the pulse width plus 100 ns. An external pulse trigger can be enabled via a BNC connector on the Lab Brick. Similarly, external pulse modulation can be applied from another BNC connector.


An optional feature of the generators is a frequency sweep triggering, which lets you control the start time of the linear frequency sweep via a TTL control signal on Sweep Trigger Input BNC connector.

As with all Lab Brick products, you can operate and control multiple instruments from a single computer by simply setting up each one as I described earlier and connect them directly to the computer via USB or through a powered USB hub.


To get started with your setup now, read the first post in this series, “Getting to Know Lab Brick Part One: Software”.

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