Waveforms
There are three main waveforms of interest:
- Predetected, ie. intermediate frequency that has not been demodulated
- AM-demodulated
- FM-demodulated
Sampled data
Waveforms are recorded by sampling the analog signals.
Saving the whole waveform lets you conduct measurements of parameters in the recording, such as:
- Rise and fall times on the AM-demodulated pulse
- Measurements of RF variations on the FM-demodulated pulse
- Phase measurements on the Pre-D recording.
A recording is also preferable when you analyse CW signals.
As the sample rate must be very high the recordings tend to be very large.
Time-Based Data (TBD)
The fundament of Time-based data is the Time Of Arrival (TOA). TOA is created by measuring the beginning of each received pulse.
The simplest way of accomplishing this is by thresholding. The time is measured as the AM-demodulated signal reaches a preset level.
Time-Based Data can also contain for example:
- Pulse Width (PW), also called Pulse Duration (PD)
- Pulse Amplitude (PA)
- Frequency (RF)
- Flags indicating Phase or Frequency modulation
- Angle of Arrival
- Pulse Repetition Interval (PRI) which is the difference between consecutive TOAs
TBD recordings are usually pretty small compared to sampled data.
Hybrids
You may come across data structures which contain Time-Based Data as well as sampled sections of AM, FM or Pre-D video during the pulse duration. This allows for detailed measurements while keeping the file size low.
2017-11-20