8.5 Ref frq
27,004,000
The reference frequency for the Si5351A synthesiser chip. If you set this to the actual oscillation
frequency of the 27MHz crystal, then the output frequency of the radio will be accurate.
Usually the 27MHz crystals oscillate between 3 to 5kHz too high. This is the reason for the default
setting of 27.004MHz (4kHz high).
You can measure the 27MHz reference value yourself if you have a reliable general coverage
receiver whose frequency is known to be accurate. There are other methods too! You could set
the signal generator to a certain frequency such as 10MHz. Then beat it against a 10MHz
reference, for example. Measurement of the audio offset would enable a calculation of what the
correct 27MHz reference value ought to be.
If a GPS unit is available, then this makes everything very simple – then you can use the GPS
calibration tools to calibrate this value (see below).
NOTE: When using the TCXO option in the QCX+ and QCX-mini models, you MUST set this
parameter manually to 25,000,000 priort to using the GPS calibration function.
To build the QCX radios for 160m operation, you must use a 12MHz crystal (in place of the
27MHz crystal) and manually set this parameter to 12,000,000 before operating the radio.
8.6 System frq
20,000,000
The system oscillator frequency. In this radio, the microcontroller clock is a 20MHz crystal. If you
are able to measure the actual 20MHz frequency (without disturbing it), you can enter the
frequency here. You could, for example, listen for the 20MHz radiation on a general coverage
receiver whose frequency indication you trust.
The 20MHz system clock is used for timing purposes only. It is not very critical, unless you intend
to operate the WSPR beacon function without a GPS.
If a GPS unit is available, then you can use the GPS calibration tools to calibrate this value (see
below).
8.7 Peak BPF
Press Select!
Pressing the “Select” button activates the signal generator on the configured frequency and
displays a bar on the screen showing the measured audio amplitude at 700Hz. The Band Pass
Filter trimmer capacitor should be adjusted for maximum measured amplitude. This process is
QCX operating manual, firmware 1.07, manual edit 0.03
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