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CW Waveform shaping
The power switch for the PA is the FD335 MOSFET. The R/C arrangement connected to the gate of
this switch controls the trailing edge shape of the CW pulse. The rising edge of the CW wave form is
set by the R/C time constant of the 0.1 uf cap connected to the gate of the three BS170s in combination
with the 47K in parallel with the 75K in series with the 10K resistor in the gate 3v bias circuit.
Currently, the rise and fall time is about 5 msec.
High Voltage/High Current PA protection
The voltage on the drain of the BS170 PA MOSFETs is divided to a lower voltage by a capacitive
divider, and rectified to a DC voltage. This is compared against a 2v reference. When the voltage on
the drain gets in the 50v range, the comparator will trigger a transistor discharges the 3v PA MOSFET
gate bias through a 10K resistor. Cutting back the gate bias will reduce the output power and thus
reduce the PA drain voltage to a save level.
In the source circuit of the BS170 PA FETs are four 1 ohm resistors. These are used to produce a
composite 0.25 ohm current sense resistor which is used to monitor the current drain of the PA. This
voltage is amplified by a 15x DC amplifier which is connected to the over voltage comparator via a
diode. In effect, the over voltage comparator will discharge the PA MOSFET 3v gate bias if either an
over voltage or an over current condition exists. In either case, the output power is reduced and both the
PA output voltage and current input are backed off, thus protecting the PA from both short circuit as
well as open circuit conditions.
AFA Frequency Counter Instructions
Introduction
The NC2030 uses an AFA to read out the frequency in morse code and is a modified version of the
ScQRPion "Stinger Singer" (a.k.a "SSS") frequency counter. On power up, the AFA delays (to wait for
the keyer chip to send "FB"), then sends "2T3T" to indicate this is a NC2030 AFA.
The counter modes are discussed below. For use in the NC2030, the power up default of the "E" mode
is the one primarily used to get a quick reading of where in the band the radio is tuned to.
The "L" mode is used when doing frequency shifts of the receiver LO when the PTO is being shifted to
get it in the right frequency range.
Counter Modes
The counter has five frequency measurement modes and two morse code announcement speeds. The
modes are summarized below in Table 1-1:
Norcal NC2030 v5
12-18-05
Page 122 of 128
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