2006 HamVention - SSTV Forum Presentation

Presentation by Dave Jones - KB4YZ


Operating Digital Radio Mondiale (DRM) with HamPAL Software






Digital Radio Mondiale (DRM) has become the primary means to send digital SSTV pictures over ham radio. Digital Radio Mondiale or DRM means "Digital World Radio". WinDRM is the current software by Cesco HB9TLK using the DRM mode. DIGTRX is the software by Roland PY4ZBZ using the DRM mode. HamPAL is the software by Erik VK4AES using the DRM mode.



What is HamPAL ?

It is software designed to run under Windows XP. It requires a fast computer - 1 GHz CPU (or faster). It is for digital transfer of image files over SSB voice bandwidth. It uses DRM encoding compatible with WinDRM and DIGTRX. It does NOT require calibration of the sound card as with analog SSTV software. The 01/JAN/2006 version of HamPAL is available for download using one of the links from the WEB page: http://kb4yz.ham.org






RECEIVING:

Select the "RX" tab to view received images. The "Progress bar" is located in the lower left corner of the RX screen. The length of this bar indicates the size of the file being received. Green represents segments received. Red represents missing segments. The "Progressive Receive" feature allows for viewing an image as it is being received. JPEG2000 image files appear distorted until all segments are received. Check the "Progressive RX" box in the lower left to enable. This feature requires the program IrfanView. Shortly after receiving begins, the filename should appear in the area just below the image on the line that says "RX filename". To the right of this filename is the number of segments needed. Below this is an area providing more information while receiving. "Total" is the number of segments in the image file. "Decoded" is the number of segments successfully decoded so far. "Decoding" is the segment number that was last decoded. "Error Hz" is the measured difference in frequency of the sending station and your receiver. A "-48" while operating Lower Side Band means that the sending station is transmitting 48 hertz below your receive frequency. In the case for Upper Side Band, it is just the opposite. The callsign of the transmitting station will appear in the upper left corner of the screen.






"RX to Full Screen" can be selected under "Setup" to automatically display the image full screen after it is received. A copy of the image in JPEG format automatically goes into the "Last RX" thumbnails.



TRANSMITTING: Images may be loaded for sending in several ways. "Load Pic" will open a dialog box listing the image files in the selected folder. Selecting one of the files will display a thumbnail view of this image. Clicking "Open" will convert the image to JPEG2000 and compress the file to the selected size set by the "Pic Size" slider. Animated GIF images will not be converted.

Right clicking the image brings up a menu that allows you to crop the image. More image editing options are available under "PicEdit" and "PicEffects". The vertical slider in the lower left may be used to resize the image. To make the resized image ready to transmit, use the "Reload TX" button. The "Load ANY" button should be used for files that are already compressed. The file will be sent "as is" with the original filename and file type. Limited color depth PNG images may be sent in this way without any corruption to image quality due to lossy compression. The "Paste to TX" is used after an image is copied to the clipboard in a paint program such as Paint Shop Pro. "Click, drag, and drop" is also possible from the thumbnails found in various pieces of software. The transmitted filename and time to transmit will appear above the image. Click the "Transmit" button to start the transmission.



REPAIR: After a transmission there may be missing segments. The receiving station will have a message on his screen showing the number of missing segments. He has the option of sending a "BSR" by clicking on the "BSR" button. This will send out a list of the missing segments called a "Bad Segment Report". If the original sending station gets this report, he may then send a "FIX" by clicking on the "FIX" button to send the necessary segnments.

Example:
Station 1 sends a picture to station 2.
Station 2 has 5 missing segments.
Station 2 sends a BSR to Station 1.
Station 1 receives the report and sends a fix to Station 2.
This process may be repeated until all segments are received properly. It is then possible to replay the transmission using the "Replay NOW" button.

The "Replay NOW" may be used anytime after a file is successfully received. Some file types require special handling. Animated GIF images may be moved from the "RX" screen to the "TX" screen using the "RX to TX" button. If the TX mode is set the same as the RX mode, clicking "Transmit" will send the file just like it was sent origionally. Using "Replay NOW" is bennifical when propagation is poor and there are many stations on frequency.

Example:
Station 1 sends a picture to stations 2, 3, 4, and 5.
Stations 3, 4, and 5 have missing segments.
Station 2 received the file successfully and does a "Replay NOW".
Stations 3, 4, and 5 are all fixed at the same time.
This is more efficient than sending the BSR and FIX for each station.





There a couple of features in HamPAL that deserve attension.

LOG:

The logging feature is automatic and can be turned on at any time to view the list of stations received. Display the list by clicking the "Log" box in the lower left of the screen. This list will display the digital callsign of any station transmitting the DRM mode. A complete transmission or full copy is not needed. With this list displayed, it is possible to scroll through the list, edit, delete, or add information. In this example, names have been added to the calls. This is very benifical since the name will always appear with the call each time a transmission is received from that station. This list is saved in a standard text file in the HamPAL folder as "calls.txt".





REPEATER:

HamPAL has a repeater function that must be activated by the user before it will function. Under "Setup" select "Show Repeater Options". A "Repeater" menu will appear in the menu bar. From this menu select "ACTIVATE AS BASE REPEATER". After clicking "OK", "***REPEATER ON***" will appear at the top of the screen. If there are only two active stations on frequency and they each have the repeater function on, each will automatically repair any transmission going from one Repeater to the other Repeater. If repeater 2 has missing segments, it will automatically send the BSR to repeater 1. Repeater 1 will automatically send the fix. The operators only need to load the pictures and click "Transmit". If the conditions are poor between the two stations, having one or two repeaters active may tie up the frequency. Caution is advised anytime the repeater is made active. The repeater may make transmissions over other stations even while another station may be talking or sending pictures. Another interesting capability of the repeater makes use of a WebCam. If a WebCam is activated with the repeater function, the repeater can automatically grab an image from the WebCam and transmit this image.

A station may access a repeater to find out if the repeater's WebCam is active. This station would bring up the "Repeater" drop down menu, then select "View Repeater Directory". This sends out a short file that tells any active HamPAL repeater to transmit the text file "repeaterdir.txt".



Here it can be seen that the "WEBCAM is ACTIVE and AVAILABLE". Next, the station would bring up the "Repeater" drop down menu, then select "Request Webcam picture from any Repeater".



This sends out a short file that tells any active HamPAL repeater to transmit a JPEG file with the name "WEBCAM" preceded by a number. The repeater can optionally include a callsign or other text and a date with time stamp as part of the picture. This feature makes it possible for a remote station to be setup with a WebCam that will send live pictures on demand without anyone at the remote site.





This presentation and other information about HamPAL will be available at the web site on this image.



The above was the Dayton Hamvention SSTV Forum presentation by Dave Jones, KB4YZ on May 20, 2006. Other speakers were Louis McFadin, W5DID and Mel Whitten, K0PFX.