CDX2000 / 13.56 MHz & 400 kHz Manual
© 2006 Comdel, Inc.
13
The outputs of this stage are:
1
44
VDC Unloaded
37 VDC
100 amps (2000W RF output)
1
+15 VDC Regulated
500 mA max.
1
-15 VDC Regulated
250 mA max.
1
-5 VDC Regulated
250 mA max
1
+5VDC Regulated
1A max
The high current required by the RF power amplifiers (PAs) is monitored by the HALL EFFECT CURRENT
MONITOR PCB (Figure FA0500RX) mounted on the 40V DC filter capacitors. This PCB uses a Hall Effect
device to monitor the DC current feeding each of the RF power amplifiers.
C. Oscillator Control Board (OCB)
The oscillator control board (Figure FA0442RX) has six parts, oscillator clock, three stages of gain, circuitry for
output power control and monitoring circuitry. The oscillator clock is a TTL compatible output device that
determines the frequency of operation. This square signal is amplified by three tuned stages of gain,
producing a relatively clean sinusoidal 1 watt output. The DC voltage that powers the last gain stage is
adjustable through control transistor Q5 to control the RF output level of the OCB.
The gain control circuitry smoothes output control and stabilizes output power against line and load variations
and limits output power during high VSWR conditions. Control is achieved through the LM 356 operational
amplifier, IC1. This op-amp compares the forward power signal (from the power monitor board) to that of the
DC reference level applied to the non-inverting input. The reference level is set either from the front panel
potentiometer or from Pin 5 of the J1 connector.
The LM 356 drives the gain control transistor, Q5, until enough signal from the forward power detector in the
directional coupler is applied to the inverting input to the op-amp. When the inverting signal equals the
reference voltage on the non-inverting input the drive level holds constant.
The non-inverting input is also the point to which some of the protection circuits connect. The CDX controller
pulls this point down when load conditions bring the amplifiers near their over-voltage, or over-current limits.
This limits the drive to the amplifiers until the match between the generator and the load is corrected.
The reflected power limiter performs in the same way when the signal from the reflected power detector in the
directional coupler reaches a pre-set limit. The Q6 transistor does the pull-down function until SWR conditions
are within safe limits. The OCB also includes linearizing circuitry allowing both forward and reflected analog
power level signals to appear at connector J1 as linear representations of the incident and reflected RF output
power. Two squaring ICs U2 and U4 are used to condition the square law signals from the directional
couplers.
Typical Specifications (OCB)
Output load impedance
50 ohms
Output RF power level
1 watt (max)
Input power
Pin 10
+15 VDC at 170 mA max
Pin 8
-5 VDC at 24 mA max
Remote power control input impedance
Pin 2 on J1
2 K ohm
Reflected power limit
Internally set to 100W
