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Separating Frequencies by Time:
Subtracting for Signal Isolation:
Ground Balancing:
Dual Pulse Advantage:
Signal Processing:
- The detector transmits two pulses with different lengths.
- The received signal is sampled at specific moments after each pulse.
- High-frequency components decay faster and disappear in later samples.
- This allows separation of high (H), medium (M), and low (L) frequencies based on the sampling time.
Subtracting for Signal Isolation:
- The H component is isolated by subtracting the M and L components (adjusted proportions) from the initial (HML) sample.
- Similarly, the M component is isolated by subtracting the L component from the ML sample.
- The L component, containing ground signals and low-frequency targets, remains separate.
Ground Balancing:
- The L component includes unwanted ground signals.
- A portion of the L component is subtracted from both the H and M channels to compensate for ground interference.
- Early models used a manual ground balance control for each channel.
Dual Pulse Advantage:
- Different pulse lengths create ground signals with different decay times.
- A target's response might be notched out in one channel due to ground cancellation but remain visible in the other channel with a different pulse length.
- This redundancy helps avoid losing targets due to ground signal timing coincidences.
Signal Processing:
- Positive and negative target signals are rectified using full-wave rectifier circuits for consistent polarity.
- A voltage comparator selects the higher-amplitude signal from both channels (H or M).
- The chosen signal is then used to modulate the audio output.
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