NASA’s Glenn Research Center has devised an efficient new method of combining primary and secondary signals with minimal loss and noise. With its ability to reduce system noise, this novel signal combiner delivers the best opportunity to receive a desired signal not easily distinguished from background noise.
Through low-loss signal combination, Glenn is leading the way to optimize radio transmission remotely during self-checking routines. Using conventional combiners in bit-error-rate testing results in a loss of 3 to 4 dB per band, and with a directional coupler, the secondary signal experiences losses of 10 dB or more. Moreover, during signal measurements, the additional components must be placed and later removed to prevent any impact to the measurement, making for a cumbersome process. Glenn’s solution is to combine the primary and secondary signals in the frequency domain through the use of a frequency division diplexer/multiplexer in combination with a wideband ADC.
The multiplexer selects one or more bands in the frequency domain, and the ADC performs a nonlinear conversion to digital domain by folding out-of-band signals in with the primary signal. NASA makes use of subsampling a given band within the ADC bandwidth to fold it into another band of interest, effectively frequency-shifting them to a common frequency bandwidth.
Glenn’s breakthrough method has two significant advantages over the conventional use of a power combiner or directional coupler in bit-error-rate testing: 1) it combines signal and noise (secondary signal) with very low loss, and 2) it enables the selection of the desired signal-to-noise ratio with no need for the later cumbersome removal of components. This streamlined process allows for invaluable in-situ or installed measurement.