6
Note that the resulting Clk0 frequency must still satisfy the range requirements of the Si5351A. In the
case of a frequency error, an error flag is set. This causes an “E” to be displayed at the top right of
the display, in the default display configuration. It is cleared by tuning to a valid frequency that is
within the Si5351A’s range.
The value entered here is the IF frequency itself. The actual output frequency of the VFO kit is
computed from the displayed frequency and the IF frequency as follows:
Positive offset: actual output frequency = IF + displayed frequency
Negative offset: actual output frequency = IF
– displayed frequency
As an example, consider the popular BITX40 40m band SSB transceiver, using this VFO kit as the
oscillator. The IF of the BITX40 is 12MHz. The analogue VFO in the BITX40 runs at 5MHz and
therefore tunes
“in reverse” – so 7.000MHz needs a VFO at 5.000MHz, and 7.100MHz needs a VFO
at 4.900MHz. When replacing the analogue oscillator in the BITX40 with this VFO kit, set this IF
Offset configuration to -012,000,000. The
“negative” sign will cause the output frequency to be
12MHz minus the displayed frequency
– which is exactly what is needed for a BITX40 VFO.
Multiplier
1
Multiplier allows you to use this signal generator as a VFO in radios where a Quadrature Sampling
Detector (for example) is required, that is clocked by a VFO signal at 4x the receive signal. The Clk0
frequency is the displayed fre offset, multiplied by the multiplier.
Note that the resulting Clk0 frequency must still satisfy the range requirements of the Si5351A. In the
case of a frequency error, an error flag is set. This causes an “E” to be displayed at the top right of
the display, in the default display configuration. It is cleared by tuning to a valid frequency that is
within the Si5351A’s range.
GPS {Mode Baud}
0 009,600
The first setting is the GPS mode. This controls how and whether GPS is used. If set to a non-zero
value, and a GPS module is connected and producing a valid 1pps signal, then the accurate time
pulses from the GPS unit will be used to discipline the output frequency(s) of the VFO/Signal
Generator.
When GPS is enabled (non-
zero mode parameter), the Si5351’s Clk2 output is set to ¼ the 27MHz
crystal reference frequency. This signal is routed to the ATmega328’s Timer1 input, and the GPS
