User Manual For V2



To install the program run the downloaded program jqamv2_setup.exe. The install wizard will guide you through the rest of the installation.


Running the program:

You will find a program shortcut in your start menu. Click Start , J-QAM , J-QAM V2. If this is the first time you have run the program a window will display telling you fftw is finding a fast implementation of an fft. Once this is gone the program is loaded.


Configuring the program:
Upon running the program, a default window will be showing.

If all you want to do is use it as a demodulator, chances are selecting file-start is enough.

Else, click the options-settings from the menu bar. The following window should be showing.



First, configure “SoundCard Settings”. Choose the “sample rate” for your sound card, I recommend 96000 but if your computer does not work well with this setting try something lower like 48000. The “buffer size” controls the size of the audio buffer and the value of 30000 should be adequate. Choose your “Soundcard Device” from the list.


Next, Decide which checkboxes you want to activate.

Configuring the demodulator.


From the settings window click on “Demodulator”



Demodulator Settings (General).


“Demodulator Advanced” is the window where all the settings of the acquisition of the signal and tracking of it live. Experiment with these if you are feeling keen.


Click “OK”, select File-start, and the program will hunt for a signal.


Configuring the modulator.


From the settings window click on “Modulator”




Next, configure “QAM settings”. Decide which checkboxes you want to activate.


Your data rate in bits per second can be worked out using the following formula.

For QAM16 datarate= ((100- RSErrorPercent)/100)*3*CenterFrequency/Gamma

For QAM64 datarate= ((100- RSErrorPercent)/100)*5*CenterFrequency/Gamma

Your bandwidth in Hertz will be


And remember

2*gamma-1 should be greater than alpha.



Station ID






Modulator UDP





Modulator Unreal Media


To run unreal media you will need to download “unreal media server”, “unreal media live server” go to http://www.umediaserver.net/umediaserver/download.html to get the two programs needed.








Modulator web server.


These are the files that J-QAM sends when there is sufficient bandwidth. Enter the size of the packet’s you wish to send, 512 should be adequate. The program only sends files when the program is not sending anything else, to do this you must specify the idle threshold. A small idle threshold means the program waits for very little activity before sending a packet of a file.  Setting this value to 5% or 10% should be fine. To allow you to change files while the program is still sending files I have added an FTP server to my program.  To have access to this FTP server you have to enter a port you want (normally “ftp” is used), what username, and what password you want. Click on the little yellow folder and browse for the file directory that you wish to be sent, all files in this directory can be sent but no directories of this directory. Because files are sent continuously in rotation, “Resends” allow you to specify on average how many times you send a particular file for each rotation. Zero means the file will never be sent and larger values will be sent more regularly.





Received files are stored in a folder named after the station ID where QAM.exe resides. The program allows easy access to these stored files by running a Web server which runs on the port “web server port”. To access it, selecting view-webserver from the main window will launch Firefox or Outlook express and open it. The web server interface looks like the picture below.



In the settings window OK excepts your settings whilst cancel reverts back to the previous setting.


What all the things mean.


Items from the “view” menu.



The constellation window gives a visual output of the received symbols.



The console window gives a display of any RS232 data or text packets. It also allows you to send text packets. Its main use is for testing purposes. Enter characters you want to send in the bottom and characters received will appear in the top.



The spectrum window shows what frequencies are being used.  If you’re listening to a valid signal you should get something that resembles the following picture.



the frequencies window shows you what frequency settings are probable.



the reception window shows you the current status of demodulation.



the transmission window shows you the current status of modulation.


Web page:

Will open your web browser and loaded J-QAM’s web server address



Starting the modulator/demodulator:

To start the modulator/demodulator simply click the start button in the main window. To stop the modulator/demodulator simply click the stop button in the main window. These are also available from File-start, and File-stop.


Jonti Olds

Email jontio@i4free.co.nz

Home Page http://wwwjontio.zapto.org

Product Page http://homepages.paradise.net.nz/peterfr2/QAM.htm