Tech Tips: Understanding the AGC & DQ Diversity Combiner Control on a Telemetry Receiver

April 30, 2018

The objective of the Diversity Combiner option on GDP’s Model 4426 Telemetry Receiver  is to process an RF signal received by two receivers to produce the best possible output by weighting and combining the two signals prior to detection. By default, the combiner weights the signals using the Automatic Gain Control (AGC) from each receiver to determine the best weighting factors to apply to each signal in the combining process. Simply put, the stronger signal gets the higher combining weight. This produces an optimal combining result when the nature of the signal impairment for both channels is Additive White Gaussian Noise (AWGN). However, when RF channel impairments are caused by something other than AWGN, for example in the case of multipath distortion, the strongest signal is not necessarily the best signal.

To address this scenario, GDP offers user selection of the combiner control. In addition to the standard AGC control, a Data Quality (DQ) control is provided. When DQ control is selected as the combiner control, the combiner uses a measure of the signal quality from each receiver to determine the combiner weights rather than the signal strength. Now instead of the stronger signal, the higher weight is applied to the signal that has a better measure of data quality

The video below demonstrates a computer screen in real-time displaying the Graphical User Interfaces for both the Model 4426 Diversity Receiver and the Model 650 Data Link Test Set.