QCX assembly Rev 1.08
102
9.3 Audio Ch.1
01,652
This item just displays the raw amplitude number calculated by the Goertzel algorithm for the
audio channel 1, which is connected to the output of the audio amplifier. The value shown here will
depend on the input signal level but also on the gain control. You can easily verify that as you turn
up the gain control knob, the displayed value increases.
9.4 Audio Ch.2
00,008
This item just displays the raw amplitude number calculated by the Goertzel algorithm for the
audio channel 2, which is connected to the output of the phase nulling circuit. The value shown
here is independent of the gain control. The value is much less than that measured on Audio Ch.1.
This is because one ADC least significant bit equates to a voltage of about 5mV. The signal
amplitude at that point in the receiver signal path is too low to produce much output from the ADC
unless the received signal is very strong.
9.5 Frequency
4.21523 MHz
This is the frequency counter. The resolution is 10Hz, which results in an update rate of around 8
times per second approximately.
The frequency counter input is connected directly to the Timer1 input of the microcontroller. There
is no pre-amplifier or level adjustment. The ATmega328P processor operates from a 5V supply. It
expects the frequency counter input signals to be of an appropriate amplitude.
According to the ATmega328P datasheet, a “low” has a maximum input voltage of 1.5V and a
“high” has a minimum input voltage of 3.5V. Therefore, the minimum amplitude signal to drive the
frequency counter successfully would be 2V peak-peak centred on a 2.5V DC offset. Exercise
great care to ensure that the voltage levels are correct, to avoid damaging the ATmega328P input
pin.
Additionally, since the ATmega328P has synchronous timer inputs, the highest frequency which
can be counted is limited to about 40% of the system clock (20MHz).
Therefore, this frequency counter has range of 0 to 8MHz. The upper frequency end of this range
will only be achieved in the case of a nice tidy squarewave of adequate amplitude an 50% duty
cycle. Lower quality signals will result in a lower upper frequency limit.
Summary of Contents for QCX 5W CW
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