Next up in the quest for the perfect FT8 decoder is the SDRplay model RSPdx. This is SDRPlay’s latest receiver. Several software packages are capable of running this SDR including the one that comes with it, SDRuno. Most popular is probably SDRConsole and it has the advantage of coming with a built-in server for remote access which is a requirement. The RSPdx antenna input is connected to an external splitter and continues on to an active receive loop, the DXEngineering RF-PRO-1B. The other output of the splitter is connected to the IC-7610 RX-IN jack. A direct comparison of the number of FT8 decodes was made by running two copies of WSJT-X simultaneously. The 7610 wins by a mile. Here are screen snaps of the same pass for the two radios. First, from the 7610.
Next, from the RSPdx.
Observing the decodes for pass 193730, the top image has 32 stations and the bottom 19. In this one pass the winner is clearly the IC-7610. The RSPdx might not be optimized considering it was just installed today. Next step is to try to optimize the RSPdx.
Trying to find a way to optimize the RSPdx performance it was found by turning the SDRConsole gains up and the agc off the same number of stations can be decoded on each radio. Gain has to be reduced to the WSJT-X application so it won’t be overdriven. The number of decodes are the same on both receivers now and the SNR (signal to noise ratio) is within a few dB. On RSPdx both the RF gain and the IF gain are set to max. Even with the gains set wide open SDRConsole is not showing any signs of overload. This result might indicate the signals from the active antenna, which are attenuated when they go through a splitter, are very weak. Still the IC-7610 has no problem with the levels and the RSPdx perhaps shouldn’t either. At least a way was found to make the performances equal. It would be interesting to remove the splitter however that would produce meaningless results since the two receivers would then be on different antennas. The new Flex radio should arrive soon and that will provide a third radio for comparison.