Driver Setup
Under construction.
Set the Amplifier Power switch and the RF Output Ctl switch to off. Connect a 50 Ohm load to RF Out and then turn on the mains power to the AOM driver using the rear power switch. You should see one green LED lit on the main board (the "Controller Pwr Okay?" LED); one Green LED lit on the power amplifier board (the "No Fault" LED); and one red LED lit on the power amplifier board (the "Sequencing" LED). If these LEDs are all on, power the amplifiers by setting the Amplifier Power switch to on. You should see an additional green LED light up on the main board (the "Pre-Amp Ready?" LED). You should also see four green LEDs turn on in sequence on the power amplifier board. The "Sequencing" LED should turn off once all the green LEDs on the power amplifier board have turned on. If you don't see 7 lit green LEDs (2 on the main board, 5 on the power amplifier board) and no lit red LEDs after flipping the Amplifier Power switch, then something is wrong with the AOM driver. If everything looks okay, turn off the Amplifier Power switch and follow the instructions for setting the power amplifier quiescent current below.
The power amplifier gate bias voltage must be set so that the quiescent current into the amplifier's drain is approximately 100 mA. The gate bias voltage is adjusted using the trimpot R21 (show in the center of the figure below).
To set the quiescent current, put the RF Output Ctl switch in the off position and attach a multimeter or scope to the Idd Monitor BNC (the BNC connector clipped by the bottom of the above figure). Turn on the power amplifier using the Amplifier Power switch. Verify that 5 green LEDs turn on (the "No Fault" LED should be steady green and the others should turn on in sequence over the course of about 1 second) and the red LED turns off. The Idd Monitor has a sensitivity of about 1 V per Amp of drain current. Adjust R21 until the multimeter attached to Idd Monitor reads between 100 mV and 110 mV. Don't worry if you're a few mV outside of this range, the trimpot has hysteresis that makes setting an accurate value for Idd challenging.
Many AOMs and EOMs can be damaged by applying excessive RF power to them. To ensure that low-power AOMs and EOMs cannot be damaged by the RF driver, an inline fixed attenuator can be installed between the pre-amplifier and the power amplifier. Possible positions for the inline attenuator are indicated by red arrows in the figure below.
The DAC voltage output to the VVA can also be restricted by setting a attenuator minimum voltage using the LCD display and rotary encoder. The attenuator minimum setting does not restrict the VVA set voltage in external or summed control modes, so relying on the attenuator minimum is not recommended when using the driver with critical or expensive devices.
To reduce harmonic distortion, the VCO has a 3 dB fixed attenuator at its output. This attenuator is labelled RF 6 and is circled in the figure below.
The power output of the box could be increased by <= 3 dB by replacing RF 6 with a 0 dB attenuator. Alternatively, harmonic distortion could be decreased by increasing the attenuation of RF 6.