The Schaffer–Vega diversity system used a
space diversity method consisting of two independent VHF receivers fed by antennas placed at least one wavelength apart. Use of two full independent
receivers, rather than two
parallel antennas, made the Schaffer-Vega the first "True Diversity" system. The diversity technique prevented
signal degradation due to multi-path cancellation. In the Schaffer-Vega system, a
comparator monitored the instantaneous
RF signal strength delivered by each antenna to its dedicated receiver, that switched to the other receiver when the currently selected receiver's signal strength fell below a
quieting threshold. The system achieved high
interference rejection by using four
helical resonator filters between the antenna and
preamplifier stage of each receiver. This made it possible to use the systems on unused
VHF television broadcast frequencies and protected the receivers from even strong spurious local signals (such as nearby police calls, taxi dispatch, etc.). Limited by the US
FCC to 50 mW output, the Schaffer-Vega Diversity System maintained reliable transmission for up to 100 meters in a line of sight from transmitter to receiver. In the United States, the FCC and corresponding agencies in most
ITU countries, regulations that limit the transmitter's
FM frequency deviation also limited the theoretical
signal-to-noise ratios and
dynamic ranges of wireless systems to approximately 70 dB. The Schaffer-Vega Diversity System also used
companding. By compressing
signal amplitude 2:1 in the transmitter and then expanding it in the receiver, it was possible for the system to deliver a signal-to-noise ratio and dynamic range of 100 dB. ==Use in the recording studio==