RtlSdrDiags: A C++ repository from wizardyesterday

This code uses librtlsdr for a basis, and I have created an AM/FM/WBFM/SSB
demodulator with this stuff.  The goal here was to keep it light weight
so that it can run on a BeagleBone Black board.

There is no GUI, but instead, I have created a command interpreter that you
access via netcat or telnet to port 20280.  You can change demodulaton modes
on the fly, and you can change various radio parameters.

Let me mention a few things.  First of all, I did *not* write the librtlsdr
code.  I've merely incorporated a snapshot of it into my code since it provides
the foundation for my system, and I want people to be able to build the code
in a standalone fashion.

Next up, I wrote my own message queue code since I needed something that
could survive newer versions of compilers.  Finally, I didn't use makefiles,
although, I don't really have anything against using make.  This occurred
because I wanted to whip something up quick and dirty.  The system grew
though, but I still don't really have any regrets as to my decision.  The
result is that the user need only have g++, and bash to build my code (and
the other people's code which I have included in the system).

Here's how you build this stuff.

1. Clone the repository.
2. Navigate to the radioDiags directory.
3. Type "sh buildLibs.sh".
4. Type "buildRadioDiags.sh.

The executable will be in radioDiags/bin/radioDiags.

Let's talk about receiver functionality first.  The demodulated output is
presented to stdout, and the format is 8000Samples/s, 16-bit, Little Endian
PCM.  You could run the program in the following manner.

bin/radioDiags | aplay -f S16_LE -r 8000

Now that the program is running, you need to connect to the command and
control link to port 20280 via netcat or telnet (I prefer netcat).  A
welcome message will appear, and if you type help, you will be presented
with a help menu.  Okay, let's say that you want to listen to a local
station on the FM broadcast band.  At my location, I would type the following:

1. "start receiver"
2. "set rxfrequency 91500000"
3. "set demodmode 3"

This starts the receiver up, sets the frequency to 91.5MHz, and the
demodulation mode to wideband FM.  If you type help, you'll see how to set
the other demodulator modes.  You can do other things also such as setting
the demodulator gains.

What if you don't have a sound card on the computer for which the software
is executing on?  For example, I use a BeagleBone Black to run the SDR code
(it's fast enough to do all the signal processing), and I use a 200MHz
Pentium 2 computer to play the sound?  Here's what I do.

On the BeagleBone Black, type the following (note that the -u argument to
netcat forces UDP usage.  If you don't have UDP support, don't use the -u
argument):

1. "bin/radioDiags | netcat -u <IP address of host computer> 8000"
2. Perform steps t to 3 above to listen to your local FM station on 91.5MHz.
  
On the host computer (the one with the sound card), type the following:
1. "netcat -l -u -p 8000 | aplay -f S16_LE -r 8000"
2. On a separate shell, type "netcat <IP address of BeagleBone Black> 20300"
3. Peform steps 1 to 3 above to listen to your local FM station on 91.5Mhz.
  
Let it be noted that all demodulated output is 8000Samples/s PCM (for all
demodulation modes).  I made this decision because I wanted to be able to
change demodulation modes on the fly.  Also note that steps 1 to 3 can be
performed in any order.  You can change any of the receiver parameters
without having to stop and restart the receiver.  Yes, there is a "stop
receiver" command.

The output of the help command appears below.

******************** Begin Help Output ********************************

set demodmode <mode: [0 (None) | 1 (AM) | 2 (FM)
                      | 3 (WBFM)] | 4 (LSB) | 5 (USB)>]
set amdemodgain <gain>
set fmdemodgain <gain>
set wbfmdemodgain <gain>
set ssbdemodgain <gain>
set rxgain [<gain in dB> | a | A]
set rxifgain <gain in dB>
enable agc
disable agc
set agctype <type: [0 (Lowpass) | 1 (Harris)]>
set agcdeadband <deadband in dB: (0 < deadband < 10)>
set agcblank <blankinglimit in ticks: (0 =< blankinglimit <= 10)>
set agcalpha <alpha: (0.001 <= alpha < 0.999)>
set agclevel <level in dBFs>
set rxfrequency <frequency in Hertz>
set rxbandwidth <bandwidth in Hertz>
set rxsamplerate <samplerate in S/s>
set rxwarp <warp in ppm>
set squelch <threshold in dBFs>
enable iqdump
disable iqdump
start receiver
stop receiver
set fscanvalues <startfrequency> <endfrequency> <stepsize>
start fscan
stop fscan
start frequencysweep <startfrequency> <stepsize> <count> <dwelltime>
stop frequencysweep
get radioinfo
get fscaninfo
get sweeperinfo
select vfourblogradio
select normalradio
get agcinfo
exit system
help
Type <^B><enter> key sequence to repeat last command

******************** End Help Output ***********************************


The output of the get radioinfo command appears below.

******************** Begin Get Radio Info Output **********************

------------------------------------------------------
Radio Internal Information
------------------------------------------------------
Receive Enabled                     : Yes
Receive Gain:                       : Auto
Receive IF Gain                     : Auto
Receive Frequency                   : 90100000 Hz
Receive Bandwidth                   : 0 Hz
Receive Sample Rate:                : 256000 S/s
Receive Frequency Warp:             : 0 ppm
Receive Timestamp                   : 39763968
Receive Block Count                 : 2427

--------------------------------------------
Data Consumer Internal Information
--------------------------------------------
Last Timestamp           : 39763968
Short Block Count        : 0

--------------------------------------------
IQ Data Processor Internal Information
--------------------------------------------
Demodulator Mode         : FM
Signal Detect Threhold   : -200 dBFs
IQ Dump Enabled          : Yes

--------------------------------------------
AM Demodulator Internal Information
--------------------------------------------
Demodulator Gain         : 300.000000

--------------------------------------------
FM Demodulator Internal Information
--------------------------------------------
Demodulator Gain         : 10185.916016

--------------------------------------------
Wideband FM Demodulator Internal Information
--------------------------------------------
Demodulator Gain         : 10185.916016

--------------------------------------------
SSB Demodulator Internal Information
--------------------------------------------
Demodulation Mode        : LSB
Demodulator Gain         : 300.000000


******************** End Get Radio Info Output *************************

The new features I have added are listed below:

1. A signal squelch that works directly with the average magnitude of
a received IQ data block.

2. A frequency scanner that lets you specify a start frequency, an end
frequency, and a frequency step. This collaborates with the squelch
such that, when scanning, if a signal exceeds the squelch threshold,
the scan will stop so that you can hear the demodulated audio of the
signal. When the signal goes away, frequency scan will continue.

3. A software automatic gain control (AGC) has been added that
controls the IF amplifier.  In addition the user now has the
capability to change the gain of the IF amplifier for more challenging
signals.

When the user types "get fscaninfo" (for the frequency scanner), the
output appears as illustrated below.  Not that the start frequency, the
end frequency, and the frequency increment are configurable.  See the
help command output for the syntax of the commands related to the
frequency scanner (fscan).

******************** Begin GetFscainfo Info Output **********************

--------------------------------------------
Frequency Scanner Internal Information
--------------------------------------------
Scanner State             : Scanning
Start Frequency           : 120350000 Hz
End Frequency             : 120550000 Hz
Frequency Increment       : 25000 Hz
Current Frequency         : 120475000 Hz

******************** End Get Fscainfo Output  **** **********************

When the user types "get agcinfo" (for the AGC), the output appears as
illustrated below.  Note that the algorithm type, lowpass filter
coefficient, and the operating point are user configurable.  See the
 help command output for the syntax of the commands related to the AGC.

******************** Begin Getagcinfo Info Output **********************

--------------------------------------------
AGC Internal Information
--------------------------------------------
AGC Emabled               : Yes
AGC Type                  : Harris
Blanking Counter          : 1 ticks
Blanking Limit            : 0 ticks
Lowpass Filter Coefficient: 0.800
Deadband                  : 1 dB
Operating Point           : -8 dBFs
IF Gain                   : 37 dB
/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/
Signal Magnitude          : 55
RSSI (After Mixer)        : -44 dBFs
/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/_/


******************** End Get Agcinfo Output  **** **********************


Anyway, if you have any questions, you can always catch me on libera IRC.
I use the nick wizardyesterday.  I can also be reached on Facebook as
Chris Gianakopoulos.

Oh one last thing.  Anybody can use my software without grief.  I guess I'll
have to put the GNU open source stuff at the beginning of my files, and that
will happen later.  Either way, feel free to use my software, sell it, or
give it away.  I believe in sharing what I create to benefit the Open Source
Community.
wizardyesterday/RtlSdrDiags
