Fixed Spectrum Range Sampling

Solutions for a fixed bandwidth sampling performs fast spectrum scans within specified range, which is not wider than Nyquist zone. Nyquist zone width strongly depends on the digitizer's capabilities. Higher sampling rates usually leads to wider Nyquist zone.

As every acquisition, processed in FFT, privides spectrum for the whole range of interest, spectrum scan rate might be very high, compared to expensive radio monitoring systems.

Fixed frequency range sampling can be implemented in two ways:

  • Sampling a certain Nyquist zone using a bandpass filter as the zone selector.
  • Moving down the range of interest using RF downconverter and sampler.

Simplified setup for undersampling mode - higher Nyquist zone sampling

FBS setup

The undersampling mode has it's limits. The dynamic range decreases with every higher Nyquist zone. The Digitizer input bandwidth is limited as well. To overcome these limits, an RF downconverter could be used.

Simplified setup with RF downconverter usage

IFS setup

This setup is similar to IF channel sampling with exeption that RF downconverter operates on a fixed frequency and is not controlled by the application.

Usage

Ultra-fast monitoring of the fixed bandwidth. Various setups can be implemented for radiospectroscopy, fixed radio spectrum bandwidth monitoring, communication control.

Devices

One of the devices, suitable for custom made RF spectrum scanning systems, is a digitizer ADQ-114 from SP Devices.

It has a sampling rate up to 800 MHz. Combining input filters with appropriate sampling frequencies it is possible to implement very fast and flexible radiomonitoring solutions for various fixed frequency ranges.

Examples of the scan rate for 400 MHz bandwidth by using different spectrum resolutions:

  • 603 MHz/s @ 1 kHz - 1.5 acquisitions/s
  • 1 600 MHz/s @ 2 kHz - 4 acquisitions/s
  • 3 080 MHz/s @ 5 kHz - 8 acquisitions/s
  • 6 700 MHz/s @ 10 kHz - 17 acquisitions/s
  • 8 400 MHz/s @ 12.5 kHz - 21 acquisitions/s
  • 11 700 MHz/s @ 25 kHz - 30 acquisitions/s
  • 15 500 MHz/s @ 50 kHz - 39 acquisitions/s

PC processing power is very important for fast scans, so quad qore processors are recommended. To achieve the results mentioned above, the PC equipped with CPU Intel Core 2 Quad - Q9550 has been used.

Any other digitizer from SP Devices might be easily integrated into such systems.

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