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Waveform-Generator
A waveform generator generates the transmitting signal on an IF- frequency. It permits generating predefined waveforms by driving the amplitudes and phase shifts of carried microwave signals. These signals may have a complex structure for a pulse compression. Since these signals are used as a reference for the receiver channels too, there are high requirements for the frequency stability.
Figure 1: an e.g. Block diagram of a waveform generator for a non-linear compressed pulse
The finally waveform is constructed of 2048 discrete voltage steps here.
Its values of amplitude and phase are stored in programmable memories
(PROM's). The processing of an
I & Q-
phase- detector is arranged reverse virtually.
This method of design the transmitting pulses hats got the advantage,
that the waveform is digitally described for a computer-controlled signal
processing. A digital processor unit can execute the
pulse compression now.
Clock-Pin
The external clock of 25 Megahertzes clocks the countercascade.
WF-Start-Pin
The trailing edge of the negative polarized „WF-Start”-Pulse triggers the flip-flop. The output enables the counter-cascade. It begins to count the clock pulses.
Enable-Flip-Flop
The flip-flop set by the „WF-Start”-Pulse generates an enable-signal for the Countercascade. The carry-pulse of the counters resets the flip-flop and the counter stops.
11-Bit Counter
The counter-cascade counts the clock pulses and generates the 11 adress bits for the memories. One loop of the counter-cascade stand for the pulsewidth of the transmitting pulse and take a time of approximately 40 microseconds.
Carry-Signal to Reset
The carry pulse of the countercascade resets the flip-flop and the counter stops to count.
11-Bit Adress-Bus
There are 11 adress bits for adressing the memories.
Sine- PROM
The whole waveform is divided into 2048 timesteps. For every timestep a 8-bit voltage value is stored in this programmable memory. This memory provides the sine wave (the In-Phase signal).
Cosine- PROM
The whole waveform is divided into 2048 timesteps. For every timestep a 8-bit voltage value is stored in this programmable memory. This memory provides the cosine wave (the Quadrature signal).
D/A-Converter
This D/A-Converter converts the 8-Bit data words into an analogue voltage. All these timesteps got an different value of voltage and these timesteps are stringed to a frequency together. The frequency can reach values from zero (DC) to 1 megahertz.
F1 Local Oscillator
This contact supplies with the unmodulated IF from an external F1 local oscillator.
Amplifier
This amplifier decouples the D/A-Converter from the load (the mixer).
Mixer
The mixer alloys the unmodulated IF-frequency and the frequencies of the modulation to the IF-Waveform.
Hybrid-Combiner
The Hybrid-Combiner is a passive pover divider intrinsically, but used „on backwards”. The both input-signals are combined phase-dependent to the finally IF- waveform of the transmitting pulse.
Waveform-Amplifier
This amplifier is a decoupler and a band pass filter simultaneously to block out the harmonic waves.
Testpoint 1
The „in-phase” part of the waveform you can measure at this testpoint.
Testpoint 2
The „quadrature” part of the waveform you can measure at this testpoint.
