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IQ Demodulator Offset Tuner (Doppler Correction)

The IQ Demodulator Offset Tuner block offers a remote control for continuous doppler corrections.

IQ Demodulator Offset Tuner block

Left hand side Input:

  • Demodulator

Right hand side Output:

  • HTTP Server


In some use cases like continuous doppler correction it is required to continuously re-tune the SPECTRAN V6. However, this would have an impact on relatively longrunning DSP operations like large FFTs. The SPECTRAN V6 would retune, while for e.g. not all FFT bins have been filled, and that leads to gaps or invalid data. Also for recording it could lead to gaps or invalid data results. This is possible using the IQ Demodulator block and its Lock Target Frequency feature.
For even more flexibility in combining various corrections, the IQ Demodulator Offset Tuner block is needed. It offers a great visualization and powerfull correction sets, making the results easier to understand and monitor:

IQ Demodulator Offset Tuner block setup

For even more flexibility in combining various corrections, the “IQ Demodulator Offset Tuner” block has been introduced. It helps you with control. Also, the IQ
Demodulator Offset Tuner” makes it easy to visualize and enter corrections more conveniently, making the results easier to understand and monitor.
The next screenshot shows the following system properties:

  • A global “Frequency Offset” of -126.000 MHz is applied. The SPECTRAN V6 gets tuned to 139.200 MHz, because the signal of interest for the Frequency Offset is set to 13.200 MHz.
  • The “IQ Demodulator” setting “Lock Target Frequency” is set, the sample rate & Span Frequency is set to 5 kHz.
  • The “IQ Demodulator Offset Tuner” applies an additional +1 MHz that results in a total system offset of 1 MHz.
  • Demodulator Tune Is set to 14.07520, Target Fixed Frequency is set to 14.075 MHz, that results in a correction of 0.2 kHz applied in the “IQ Demodulator”.

The “IQ Demodulator Offset Tuner” is the best solution to remote control for e.g. continuous doppler corrections. Let’s say you want to update the demodulator
center frequency from a remote system, that calculates the required signal of interest frequency. First we use the HTTP connector of the “IQ Demulator Offset
Tuner” and connect it to a HTTP Server block. Use the following request to apply the remoteconfig to our block. Be sure to use the corresponding receiverName /
name of the configuration:

content-type: application/json
"receiverName":"Block_IQ Demodulator Offset Tuner_1",
"name":"Block_IQ Demodulator Offset Tuner_1",

Tuning the “fDemodTune” property of the “IQ Demodulator Offset Tuner” keeps you DSP Blockgraph continuously streaming at the fixed target frequency,
while the applied offset is reflected in the yellow label in the UI of the “IQ Demodulator Offset Tuner”.
Note: if only a single global frequency offset applies, as in the illustrated example, the “Frequency Offset Block” is redundant with the “IQ Demodulator Offset
Tuner” “Global Offset” setting. So, the “Frequency Offset” block could be removed from the mission while only maintaining the “Global Offset” property.


Typical IQ Demodulator Offset Tuner running Mission


A typical mission:

Typical IQ Demodulator Offset Tuner Mission

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