CDX2000 / 13.56 MHz & 400 kHz Manual
© 2006 Comdel, Inc.
14
D. Driver
The CDX2000 driver is a two-stage Class "C" amplifier with feedback. The first transistor amplifies a
1 watt (typical) input from the OCB to about 5 watts. The circuitry between the two stages include two
wideband impedance matching transformers and a loss section. The loss section provides added stability to
the system and isolation between stages. The second stage of the driver sends 20 watts (max) to the driver
output connector. There are no adjustments or tuning required for this module.
Typical Specifications (Driver)
Gain 15
dB
Input power
1 watts (max)
Output power
50 watts
Input impedance
50 ohms
Output impedance
50 ohms
Collector voltage at full power *
40 VDC
Current at full power *
1.4 A
* 1250 watts into 50 ohm resistive load
E. PA1250S Power Amplifier
The PA1250S uses four power transistors arranged in four pairs of push-pull Class "C" amplifiers. The input
power from the driver is matched with a wideband transformer, T1. The driver input is then split into four
signals and fed into four push-pull transformers, T2. Each of these transformers drives the bases of each pair
of power transistors, Q1-Q8. The transistors are operated common emitter with feedback.
The collector signals are coupled by a four push-pull transformers. The output of these transformers is once
again added together in a four-way hybrid combiner. There are no adjustments on the PA1250S.
Typical Specifications (PA1250S)
Gain 15
dB
Input power
20 watts
Output power
1500 watts (min)
Input impedance
50 ohms
Output impedance
50 ohms
Collector voltage *
37 VDC
Current draw *
50 ADC
* At 1250 watt system output into 50 ohm resistive load
F. LF1250 Power Amplifier
The LF1250 power amplifier in the CDX2000 is an eight device push-pull Class ‘D’ amplifier, with all devices
mounted on a water-cooled copper heatsink. Each device (transistor) is rated to produce over 300 Watts of
power, giving a total potential output power of 2500 watts per amplifier. This conservative approach gives a
large margin of reliability and immunity to large load impedance fluctuations and gives the CDX2000 the ability
to deliver large amounts of power into less than ideal load conditions. The output devices are FETs with
paralleled gates. The gate drive consists of two FET gate drive ICs U1 & U2. Peak voltage detector diodes
D9 & D10 are used by the front panel monitoring circuitry to limit peak voltages seen by the devices. The
output impedance of the LF1250 amplifier is about 15 ohms.
G. Directional
Coupler
Board
The directional coupler board (Figure FA0129RX) is a detector which produces voltages proportional to the
square of both forward and reflected power for both the 13.56 MHz and 400 kHz RF outputs. The signals from
the detectors are produced from current and voltage taps off the output lines.
