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Author Topic: Digital Voice (Shortwave)  (Read 2992 times)
WJ5MH
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Posts: 21


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« on: January 03, 2003, 07:58:13 PM »

Is there a 455 kHz to 12 kHz down-converter available stateside for digital decoding shortwave DRM tests?

Thanks and 73,
Joe ( WJ5MH )
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N5EIL
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Posts: 121




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« Reply #1 on: February 02, 2003, 05:22:53 PM »

what type of mode are you doing down there ... I have an old receiver that willl go to .001 MHz ...
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M1KTA
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Posts: 32




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« Reply #2 on: September 11, 2004, 01:19:52 PM »

You might want to look at this as well...

HamDReaM – Digital Voice over HF
Mel Whitten, KØPFX

Digital Radio Mondiale (DRM) is a relative new (2003) digital radio standard for international SW/MW/LW bands.  This standard was made up by a non-profit consortium in co-operation with the ITU.  Dream is an open source software implementation of DRM and was developed by the University of Darmstadat in Germany allowing free reception of digital voice (and multi-media).  This open source DRM project may be found at  www.sourceforge.net/projects/drm/.  Cesco, HB9TLK has modified this software so it will fit into narrower bandwidth of 2.3kHz SSB channel and removed the requirement for a connection to the receiver’s IF via a hardware converter to the PC’s soundcard.  In addition, he added a Linear Predictive Coder (LPC-10) audio coder/compressor found at www.hawksoft.com/hawkvoice/ . to provide noise-free “communications” voice quality on our HF bands.  Hamdream is capable of SVD, simultaneous voice and data.
Here are the steps you may follow for setting up your PC and transceiver for Hamdream:

Step – 1 (Translate existing documentation)
Go to www.altavista.com and search for PY4ZBZ:
You should find www.qsl.net/py4zbz and then,
click on “translate” (Portuguese to English)
(AltaVista does a better job on the translation than Google!)
Roland’s site has screen shots of Hamdream and has
links to sites describing in detail how DRM works.


Step - 2 (Further reading and software)
To further enhance your understanding of Hamdream:
Go to www.qslnet.de/member/hb9tlk/  
(read everything on that site, at least the English anyway!)
Look at his Hamdream screen shots of the TX and RX.
There are some sound recordings of Hamdream transmissions also.
Go to www.tu-darmstadt.de/fb/et/uet/fguet/mitarbeiter/vf/DRM/documentation.html
(this is the DRM Receiver Documentation most of it applies to Hamdream receiver).

Step – 3 (Download)
Make a “Hamdream” directory.
Go to www.qslnet.de/member/hb9tlk/
(this site seems to be the fastest
and has the latest version)    

Download and unzip into the hamdream directory:

Freeimage.dll
qt-mt230nc.dll
starttx.bat
hamdream24.exe
Source (sub-directory)

Note: Winzip or whatever you use to unzip the directory, will also include the source files and they will be extracted in a “Source” sub-directory under Hamdream.  Other digital mode sites are beginning to make this software available also.   www.qsl.net/ik1hgi/digital/programmi.htm   (English)
Locate any small jpeg file (10-15kb) and put it in your
hamdream directory for later transmission over the air.

Step – 4 (Setup)
Hamdream “should” work with -most- sound cards.  I have it running on a lap top and a clone PC.  Hamdream will also
recognize multiple soundcards, more on this later.  
PC to transceiver connections:
(Connections and set up is same as other digital modes such as PSK31/MT63 except a microphone is needed at the PC for voice).
1.   Connect any PC type mic to the MIC input of your sound card.
2.   Connect output of your transceiver’s speaker to the LINE IN of your soundcard.  This should be done using a small audio isolation
      transformer to avoid ground loop induced noise from the cable’s shield to signal lead.
3.   Hamdream uses your serial port’s RTS or DTR (I have not verified which one, but I know DTR works) to control the transceiver’s PTT line.  RIGblaster or other interfaces will take care of this requirement.  VOX could be used, but I have not tried it.
4.   Go to your PC’s mixer and set LINE IN and MIC “sliders” to approximately
      ¾ way UP.  You may need to adjust these levels later.  If you are not
      using a commercial sound card interface for digital modes (i.e RIGBlaster),
      then connect a cable between the sound card’s SPEAKER OUT and
      the MIC input of your transceiver.  This line should also be isolated.
5.Set your VOLUME OUT (speaker out of soundcard) to approximately ¼ way up on slider.
      This should be about the same level as set for other digital modes.  This is the
      data stream out that will be modulating your rig (mic out) – important level

Step – 5 (Receiving)
In the Hamdream directory, click on hamdream24.exe   A small screen will pop up, with “SCANNING...” in large letters.  Hamdream is now looking for a  hamdream TX signal from your transceiver’s speaker.  The “Input Level [dB]” should be bobbin’ up and down showing the level of audio being received.  If it is not, verify that you have audio coming in (from your transceiver) to the LINE IN by checking your mixer.  Be sure LINE IN is “checked” and the slider level is up.
Note: If you sound card does not have a LINE IN, you can use the MIC input, but  will have to share this with the MIC for transmitting.
 
Go to “Settings” then “Evaluation dialog...” and open up this screen.  Find the LED “I/O Interface” - it should be GREEN.  This verifies the program has found your sound card and it is ready to receive data.  If not, go back to the main screen and under “Settings” verify info for sound in and sound out.  Your sound card’s name or mixer info should be here, however with only one sound card, the default Wave Mapper recording/playback setting will work also.  No changes need to be made in the evaluation screen to receive Hamdream’s voice, short messages or jpeg files. Refer to the screen shots on PY7ZBZ’s web site. I have not been successful in “recording” a wave file from the Evaluation screen’s “Save Audio as WAV”.  Hamdream is normally received in USB.

Usually, the first info you will see upon receiving a Hamdream transmission is small text in red letters within the big black box followed by the transmitting station’s call sign replacing the words “Scanning...”  If the transmitting hamdream station is sending a “text message”, you will see it appear in the top upper right.  More info will pop up under the received station’s call sign and button 1- again, refer to the screen shots on the web sites.  Information such as Bit Rate, EEP (Equal Error Protection) ID:73, ACC audio compression, language used, etc. will be received.

Before any “voice” will be heard from the transmitting station, all three “Status”LEDs on the opening screen must turn Green at the receiver.  You may see one bounce back to red once in a while, but with a good signal, these will remain Green.  Depending on band conditions, sync may take only a few seconds or 15-30 seconds (higher SNR = faster sync).  You may have to be a little patient!  Open up the “Evaluation” screen and follow the progress of the LEDs.  They will be off, then change to red and finally, all green.  Refer to the “Dream DRM Receiver Documentation” for further description of the Evaluation Dialog.

Generally, when I am on the air, I transmit for 15-20 seconds before I begin speaking into the Mic to ensure the distant “receiver” is in sync.  Like the AOR ARD 9800, initial contacts are best made with schedules and using a messenger service so you can converse over the internet while setting up the contact.  It is best to start with USB SSB to ensure you are both on same frequency. There is no “tuning” indicator and no “tuning around” should be done on the signal!  I have not had enough experience to know how much (if any) buffering the transmitter side has available before sync has been established.

Step - 6 (Transmitting)
In the hamdream directory:

Click on “starttx24.bat” to execute a windows system32 “cmd.exe” file and then hamdream24.exe -t  transmitter.  

Enter your call sign in the block next to “Label”. This will generate another file in the hamdream directory which the program will read at the next bootup (settings.txt) along with you soundcard info.  

For now, leave everything else at default.  Note: User entered data for Language, Program Type, Text Message, and Slide Show Application jpeg file source will not be saved in the settings.txt file.

To transmit:  
Assuming you have your transceiver set up for normal USB SSB transmission, hamdream should be ready for a contact. Click on the “Start” button.  This should turn on your TX (PTT line) and began (some delay may occur) transmitting data into your transceiver’s MIC.  Check power out/ALC action etc. About 25 watts for a 100w transceiver is plenty.  If you have a way to monitor your signal, listen for the data.  It kind of reminds me of an old diesel engine at fast idle (well, sorta..)  Wait 15-20 seconds, and then begin speaking into the PC’s MIC. You should see the “INPUT” bar jump up to about -15 to -10.  Tx requires a pretty high level to be heard best on the receive end.  Note: Unlike the ARD 9800, a slight ‘delay’ may be experienced.  Remember, this is being done in “software” and not in a fast hardware vocoder!  Give it some time and play around with it for while until you get feel of it.  The processing time of the PC is a factor of course.  A 700mhz Pentium or better is recommended, although a slower PC has proven to run the software.

Options to try...
For Hamdream to send a Text message, the bandwidth must be changed from 2.25 to 2.5kHz or higher.  Digital voice quality appears to sound better at this higher band width (still legal in US!) and 2.5 is what I normally use.  Wider bandwidths could be used, but your transceiver may not pass them without some serious attenuation.  Once set to 2.5, you may “Add” a new message under “New” (then type the message) and click on “Add”, it will then become #2 and up.  These text messages (and jpeg files) are continuously being transmitted and will roll over. Note: To use 4.5 or 5kHz BW, change IF to 3000 Hz (not for USA HF!)For Hamdream to send a jpeg image, click on “Enable” to set up for sending a jpeg file.  If you have added a small jpeg file in your Hamdream directory, then clicking on “Add” will pop up the directory allowing you to add it.  It will now transmit he file, albeit slowly, but it will, well, eventually. My first jepg file was of Michael Powell with a great big smile... I think that he would have liked that, if he had been monitoring?  This is called the “Multimedia” dialog in the receiver. I usually keep it’s window open with the receiver so I know when a pix is received. When the file is completely received, it just “pops up” in the multimedia dialog window.  Again, more info on this in the DRM receiver documentation on the web. The MSC led (top LED on opening RX screen) will not turn green for multimedia since it is for the main service channel for voice only.

Step – 7 (Where do I try this out?)
We are back to the problem most of us had with the ARD 9800, frequency and time.  I still do not have an answer for this.  I have read, but not heard, there has been activity around 14.255. I have been using 14.236 since this is near (and also used by) the digital SSTV-ers.  Less “objection” to digital noise may be experienced here.  Again, I think skeds have to be set and go from there.  HB9TLK.s web site has a link to show you are on-the-air with hamdream.  So please use this service so others can see your call/location/freq.  You may want to try hamdream on VHF or UHF. You can bring up the IF frequency to ~3000 which will increase data rate to 8+kbps with 64-QAM. There is a lot of information on DRM available on the web.  I think you will find it fun to try out and experiment using the different settings for transmit and receive.  

I wish to thank Cesco, HB9TLK for his effort in bringing this program to the ham community and PY7ZBZ for his work in documenting the first hamdream contact “in the world”.

GL and I hope to “multi-media” with you on the air soon.  

73,

Mel, K0PFX
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