RSP2 antenna connections are a useful addition. With such a broad frequency range available, you will want several different antennas.
The new RSP2 from SDRPlay provides three antenna connectors: A, B and High-Z. You can switch in different antennas using software, which can be useful.
Ports A and B are general purpose RSP2 antenna connections with SMA connectors. Each of these covers the full frequency range. Signals received on these connectors can pass through a low noise amplifier as well as several low, high and bandpass filters. The RSP2 configures the filters automatically depending on frequency tuned. In addition, connection B can be configured to provide phantom power to an amplifier, antenna or antenna switch (4.7V at 100 ma). This is enough power for some external amplifiers. But most of the popular active antennas I have seen require 12 volts.
Folks who monitor shortwave and lower frequencies (up to 30 MHz) will appreciate the third antenna connector. This is a high impedance port that can accommodate balanced or unbalanced feed lines. Impedance is set to 1000 ohms. Unlike the SMA inputs, the High-Z connection bypasses all of the front end filtering and goes straight to the tuner chip.
If you are interested in more details, check out this video from SDRPlay.
Trying Out the RSP2 Antenna Connections
In my radio shack, I have standardized on RG-6 coax with F connectors for my receive equipment. Yes, this results in a slight mismatch with 75 ohms rather than 50 ohms. But I have found it to be effective and convenient. Impedance matching is not such a big deal for receiving on lower frequencies.
My HF antennas work fine for reception under 30 MHz on either the SMA or High-Z RSP2 antenna connections. As far as signal strength goes, I do not notice much difference. The High-Z input might be improved if I build or buy a 9:1 impedance matching transformer, though. SDRPlay suggests using this transformer from NooElec.
However, since the High-Z input bypasses most filtering, I did notice increased susceptibility to overload and inter modulation. The SDRPlay devices are not really radios, but rather radio spectrum processors with a wide range of gain options that need to be tweaked. More on that later.