The originality of this description is that the generation of tones BF is made using a DDS . And this not by using a special build , but easy to find in the drawer bottoms circuit components .
The main features of this assembly are :
– Generation 2 frequency 800 Hz or 400 + 1000 + 2600 Hz ( by moving a jumper)
– Generation of a single frequency of 1000 Hz
– Adjustable output level of a min level . 100 mV dc 600 Ohm 35.4 mV rms . in single frequency or 25.0 mV rms . 2 tones
– Spectral between 0.3 and 150 kHz sup Purity . 50dB
– Distortion lower than 0.01 % (by SFN )
– Powered by 9V battery consumption 8 mA or 50 hours of operation with alkaline battery .
– Switching automatic switching PTT .
Principle of Operation
How does a DDS?
In its simplest form, a DDS consists of a precision oscillator , an address counter , a prom containing the code and (analog digital / ) D / A converter . This is the solution that was chosen for this description.
Unlike the two frequencies generated mode 800/1000 Hz is 200 Hz or multiples in the case of the couple 400/2600 Hz signal is therefore renews at most every 5ms . To retain its simplicity in assembly, EPROM is addressed in binary mode and the software is written accordingly. With a 14-bit divider , the necessary crystal frequency of 3.2768 MHz is , which is fortunately a standard value .
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