2
ISOMET
1.
GENERAL
The RFA920T combined Driver and Power Amplifier, Figure 1, is a modular, swept-frequency RF
power source specifically designed to operate with Isomet acousto-optic deflectors. The driver
accepts a tuning voltage between approxi0 volts and +10 volts and provides an RF output to
at the selected frequency. The driver also accepts an analogue modulating signal and generates a
modulated RF output to the acousto-optic deflector. This provides for intensity control across the
scan range.
A summary of the driver specification is shown in the following table:
Model
Output Frequency
Output Power
RFA920T-80
60 - 100MHz
> 25.0 Watt
RFA920T-110 90 - 130MHz
> 25.0 Watt
RFA920T-150 125 - 175MHz
> 15.0 Watt
Figure 2 is a block diagram of the Driver. The output frequency of the driver is controlled by a
hyridized varactor voltage controlled oscillator. The output frequency is proportional to the input
tuning voltage with a scale factor of approximately 2 - 4MHz/volt depending on the model. The start
frequency corresponding to a tuning voltage of 0.0 volts is defined by the frequency offset
potentiometer (Multi-
turn put to the right of the LED’s) This permits adjustment of the start frequency
from approx -5% / +90% of the range The start frequency corresponds to a tuning voltage of 0.0 volts
and is pre-set to a start frequency as listed above. A table of output frequency versus input tuning
voltage is supplied with each driver and is pseudo-linear. The frequency linearity is typically less than
±2.0%, and frequency stability is typically ±0.25%.
A high-frequency, diode ring mixer is used to amplitude-modulate the RF carrier. A
“video”
modulation input swing of 10volts (positive with respect to ground) will result in 100% depth of
modulation. Figure 3 shows the modulation control.
The video input level must not exceed 20 volts
