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- AD9854 DDS
project
- A short article of the project and a control program for PC
- VCO frequency
calculation program
- For calculating VCO's frequency tuning range.
The resonant circuit is
so much general, that it can be used for wide range of VCOs.
The
capacitance of the varactor diode is given at min. max. and center tuning
voltage.
For the inductive component a combination of series LC and a
transmission line can be given. The transmission line can be specified by
either electrical or mechanical (microstrip) dimensions.
- Passive PLL
filter calculation program
- For calculating filter component values and other PLL numbers
- A control
program for MB1501, MB1502 and LMX1501 frequency synthesizer ICs
- It is intented for testing a synthesizer using PC to load the serial
codes.
There is also frequency hopping mode for testing frequency
switching and settling time.
- Assembler source
codes for controlling the same ICs with PIC16F84
- These are simple programs for 70 cm RX LO synthesizer. Frequency
channels can be
changed by calculating new division ratios and editing
the code.
These synthesizer ICs are common in older 450 MHz radiotelephones made by
Nokia, which are popular ham projects for 70 cm FM.
On connecting electronic circuits to parallel port
Some caution is in order when connecting external circuits to PC. There is
possibility, that voltage or current ratings are exceeded in some
circumstances, allthough breakdowns of devices are not very common. In my
opinion one should consider the following with every connection.
- If the grounds are not connected together, is there possibility, that
high voltages exist due to mains leak.
- If the other side is off and other side in life, is there possibility of
too high current somewhere.
Generally it is recommended to keep your hands off the connector
when power is on.
For overcurrent protection one frequently sees series
resistors of 1k or more in lines, when the parallel port is connected to
CMOS logic. Another alternative is the interface I used with AD9854. These work
if the data rate is not too high.
Old TTL was by nature quite robust, but nowadays there exists all kind of
logic with protection diodes, which may heavily load the driving stage.
Never seen a good treatise of this area by someone who knows, not just
having read books.
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