I like listening to my Redsun RP2100. Someday I bought an USB stick using the RTL2832U chip, and played around with SDR#.

RTL2832U USB sticks open a door to cheap and portable SDRs. GnuRadio is a powerful toolkit that provides signal processing blocks to implement software-defined radios and signal processing systems, but it is also not an easy job to get it run on Windows.

As I am majoring in communication systems, and have done lots of work on software-defined radios (SDR), such as developing receivers on customized vector processors, and Pascal is the first programming language that I have ever learned, LazRadio is born.

Here is a brief introduction.

Message Queue

Each module (or block) has a message queue. Messages in each queue are processed one after another.

There is a unique run queue (TRadioRunQueue) which creates several working threads and schedules them to serve the message queues.

Each message is composed of two fields (ParamL/H) of type PtrUInt, and a message ID obviously.

Data Transfer

Data are transfered from a source port of a module to a target port of another module by the RM_DATA message.

Data (array of Complex) is managed by TRadioDataStream, can be sent to multiple modules, and is recycled after all receiving modules have processed the RM_DATA message.

Connections

Message are passing along module connections. There are two type of connections, data connection for RM_DATA and feature connection for all other messages.

“LazRadio” Language

A system is described by the “LazRadio” language, or rather Pascal inspired by Erlang.

Although LazRadio is quite new, it’s already possible to make some fun: make a dual-FM-receiver, listening to two programs simultaneously, one ear one program or mixed as you like.

At last, below is a simulation of a classic encrypted telephone, in which the spectrum of speech is reversed.

lazradio encrypt-telephone;

var
  mic: AudioIn;
  speaker: AudioOut;
  voice-bpf1: Filter;  // '-' can be used in identifiers
  voice-bpf2: Filter;
  voice-bpf3: Filter;
  up-converter1: FreqMixer;
  up-converter2: FreqMixer;
  s-reversed: Spectrum;
  s-recovered: Spectrum;
  amix: AudioMixer;

begin
  // => connect both feature and data
  // -> data connection
  // :> feature connection
  mic => voice-bpf1 => up-converter1 => voice-bpf2
                    => up-converter2 => voice-bpf3;

  voice-bpf2 => s-reversed;
  voice-bpf2 => amix => speaker;

  voice-bpf3 => s-recovered;
  voice-bpf3 -> [1]amix;    // connect to target port 1 of amix

  // use '!' to send messages
  // set these filters as BPF, passband [300, 3400]kHz.
  voice-bpf1 ! {RM_SET_FEATURE, RM_FEATURE_SAMPLE_RATE, 44100}
             ! {RM_FILTER_CONFIG, FILTER_COEFF_DOMAIN, FILTER_COEFF_DOMAIN_REAL}
             ! {RM_FILTER_CONFIG, FILTER_TAPS, 200}
             ! {RM_SPECTRUM_BAND_SELECT_1, 300, 3400};
  voice-bpf2 ! {RM_SET_FEATURE, RM_FEATURE_SAMPLE_RATE, 44100}
             ! {RM_FILTER_CONFIG, FILTER_COEFF_DOMAIN, FILTER_COEFF_DOMAIN_REAL}
             ! {RM_FILTER_CONFIG, FILTER_TAPS, 200}
             ! {RM_SPECTRUM_BAND_SELECT_1, 300, 3400};
  voice-bpf3 ! {RM_SET_FEATURE, RM_FEATURE_SAMPLE_RATE, 44100}
             ! {RM_FILTER_CONFIG, FILTER_COEFF_DOMAIN, FILTER_COEFF_DOMAIN_REAL}
             ! {RM_FILTER_CONFIG, FILTER_TAPS, 200}
             ! {RM_SPECTRUM_BAND_SELECT_1, 300, 3400};

  up-converter1 ! {RM_SET_FEATURE, RM_FEATURE_SAMPLE_RATE, 44100}
                ! {RM_FREQMIXER_SET_FREQ, 3400 + 300, 1};
  up-converter2 ! {RM_SET_FEATURE, RM_FEATURE_SAMPLE_RATE, 44100}
                ! {RM_FREQMIXER_SET_FREQ, 3400 + 300, 1};

  s-reversed    ! {RM_SPECTRUM_CFG, SET_CENTER_FREQ, 0}
                ! {RM_SPECTRUM_CFG, SET_SPAN, 10000};
  s-recovered   ! {RM_SPECTRUM_CFG, SET_CENTER_FREQ, 0}
                ! {RM_SPECTRUM_CFG, SET_SPAN, 10000};

  // encrypted signal send to left channel, decrypted signal to right channel
  amix ! {RM_AUDIOMIXER_CFG, AUDIOMIXER_STREAM_NUM, 2}
       ! {RM_AUDIOMIXER_SET_STREAM_OUPUT, 0, AUDIOMIXER_STREAM_OUTPUT_I_I}
       ! {RM_AUDIOMIXER_SET_STREAM_OUPUT, 1, AUDIOMIXER_STREAM_OUTPUT_I_Q};
end.