Add Support for SDRPlay / Airspy

[ChrisDev8]

Add Support for More SDRs

The DSD forks are missing support for other Software Defined Radios such as the Airspy R2, SDRPlay RSP devices, etc. Adding support for these higher samplerate devices allows decoding multiple systems and/or sites with only one SDR. Problem is that the codebase is coded around the RTL-SDR so I believe the project maintainer should add a modular way of adding support for different SDR devices natively with/without using SoapySDR. Personally I have a SDRPlay RSP1B and would be happy to test the software from a SDRPlay RSP1b with P25 Phase 1 systems.

My Hardware

1. SDRPlay RSP1b and two discone antennas,
2. Arch Linux (main), Linux Mint, Fedora, and DragonOS,
3. Framework 13 AMD Edition

[arancormonk]

i've added soapysdr support: https://github.com/arancormonk/dsd-neo/blob/main/docs/soapysdr.md

i tested using rtlsdr through soapy backend and it seems to work...

give it a shot with the SDRPlay and let me know how it works!

[ChrisDev8]

So i've tried your soapysdr fix however it doesn't seem to be decoding anything.

• First, does dsd-neo decode the control channel or individual channels for p25p1 decoding? The channel file i'm using has both control and individual channels so what do I put there. The frequency seems to be pinned at the frequency specified with rtl_freq and the config keeps removing my custom profile every autosave.
• Second, the gain, bandwidth, and autogain controls for my SDRPlay doesn't seem to be implemented properly, as the program likely expects a soapysdr rtl-sdr driver. Also sdrplay has fm bandstop filter and dab bandstop filter that needs to be implemented. I would suggest adding specific arguments to the config file for these options or allow the user to customize the argument string. Below are multiple screenshots and outputs for debuging.

$ SoapySDRUtil --probe="driver=sdrplay"

-- Device identification
----------------------------------------------------
  driver=SDRplay
  hardware=RSP1B
  sdrplay_api_api_version=3.150000
  sdrplay_api_hw_version=6

----------------------------------------------------
-- Peripheral summary
----------------------------------------------------
  Channels: 1 Rx, 0 Tx
  Timestamps: NO
  Other Settings:
     * RF Gain Select - RF Gain Select
       [key=rfgain_sel, default=4, type=string, options=(0, 1, 2, 3, 4, 5, 6, 7, 8, 9)]
     * IQ Correction - IQ Correction Control
       [key=iqcorr_ctrl, default=true, type=bool]
     * AGC Setpoint - AGC Setpoint (dBfs)
       [key=agc_setpoint, default=-30, type=int, range=[-60, 0]]
     * BiasT Enable - BiasT Control
       [key=biasT_ctrl, default=true, type=bool]
     * RfNotch Enable - RF Notch Filter Control
       [key=rfnotch_ctrl, default=true, type=bool]
     * DabNotch Enable - DAB Notch Filter Control
       [key=dabnotch_ctrl, default=true, type=bool]

----------------------------------------------------
-- RX Channel 0
----------------------------------------------------
  Full-duplex: NO
  Supports AGC: YES
  Stream formats: CS16, CF32
  Native format: CS16 [full-scale=32767]
  Antennas: RX
  Corrections: DC removal
  Full gain range: [0, 48] dB
    IFGR gain range: [20, 59] dB
    RFGR gain range: [0, 9] dB
  Full freq range: [0.001, 2000] MHz
    RF freq range: [0.001, 2000] MHz
    CORR freq range:  MHz
  Sample rates: 0.0625, 0.096, 0.125, 0.192, 0.25, 0.384, 0.5, 0.768, 1, [2, 10.66] MSps
  Filter bandwidths: 0.2, 0.3, 0.6, 1.536, 5, 6, 7, 8 MHz

$ build/dev-debug/apps/dsd-cli/dsd-neo --config ~/.config/dsd-neo/config.ini --profile p25_trunk -N

[arancormonk]

I tracked this down to two separate runtime bugs and fixed both on my side.

1. --config ... --profile p25_trunk -N was unintentionally disabling trunking unless -T or -Y was also present. That meant the receiver stayed parked on rtl_freq instead of following P25 grants.
2. Autosave was writing the merged effective config back into the base INI, which flattened away [profile.*] sections. Profile-based runs now disable autosave so the source config is not destroyed.

So with the updated build (23d9e5f), your existing command should preserve the selected profile’s trunking settings:
build/dev-debug/apps/dsd-cli/dsd-neo --config ~/.config/dsd-neo/config.ini --profile p25_trunk -N

For P25 specifically, dsd-neo should sit on the control channel and retune to granted voice channels when trunking is enabled. In many P25 cases the system can learn channel mapping from control channel traffic, so a channel CSV is
often optional; if you do use one, it needs to be a channel-number-to-frequency map, not just a mixed list of control and voice frequencies.

What is still not fixed in this patch is the SDRplay-specific Soapy control surface. The current Soapy path only uses generic Soapy controls like frequency, sample rate, gain/AGC, and bandwidth. Device-specific settings from your
probe output such as rfnotch_ctrl, dabnotch_ctrl, biasT_ctrl, and agc_setpoint still need explicit support. I don't have an SDRplay to test this properly, so I'll address this as best as I can in future commits.

[ChrisDev8]

Another option for working with SDRplay devices is to add native support through the SDRplay API, the documentation is on their website. However their drivers are closed source but all sdr apps that use the API work fine with no issues. Both SDR++ and SDRAngel use native driver support for SDRplay and have no issues. For other sdr devices such as airspy, their drivers are open source such as libairspy and libairspyhf libraries.

SDRplay Documentation: SDRplay Developers PDF Documentation

My question is can you follow p25 system through tcp pcm audio and rigctl? Thinking about using SDR++ and dsd-neo.