Daz Man in Australia prepared this description of a Shortwave Radiogram HamDRM experiment …

SHORTWAVE RADIOGRAM 200 IN HAM-DRM ON WRMI!

0800 UTC Wednesday April 21 on 5850kHz and 7730kHz
0300 UTC Sunday April 25 on 7780kHz
0800 UTC Wednesday April 28 on 5850kHz and 7730kHz

How to view:

Open the folder where your decoder saves the images (in EasyDRF, click the “Rx Files” button).

When the html INDEX file decodes and saves, drag and drop it into a web browser window.

If you aren’t using EasyDRF, extract the html.gz and save it to the same folder where your decoder saves the received files (important). Then open the html in a web browser.

Once the html is open in the browser window, the browser will automatically attempt to load the images as they decode and save.

Be patient! The entire set of files takes almost 30 mins to send.

For error correction, the html file is sent 3 times. The images are sent 2 times. If you have good reception, the last image will display before the data has finished transmitting. This is normal.

If you are using a decoder other than EasyDRF, see “Known Issues” at the end of this text.

Decoder Programs

Windows: EasyDRF, WinDRM, EasyPal, DIGTRX
Linux: QSSTV, TRXAMADRM

EasyDRF is recommended, if your system will run it:
https://github.com/DazDSP/EasyDRF/tree/master/Release
(Bare application exe, no installer. To install, make a new folder and move the exe into it, then run it. The application is unsigned, so you may get a warning.)

File Decompressor (needed for 7zip or gzip compressed HTML only)
Windows: 7zip
Linux: p7zip

EasyDRF will automatically unzip the html sent on this broadcast (no decompressor necessary). Users of other decoding apps will still need 7zip/p7zip/gzip.

RECOMMENDED SETTINGS FOR HAM-DRM RECEPTION FROM AM SHORTWAVE BROADCAST

Best: AM Sync demodulation via SDR with both sidebands, using “Antifading” or similar technology to combine both sidebands in-phase at all times (SDR Sharp can do this)
2nd best: AM Sync demodulation using both sidebands combined
3rd best: AM Sync demodulation using just one sideband
…..or: SSB demodulation using just one sideband

Ham-DRM needs low distortion levels and a flat and stable phase/delay response.
Keep audio levels high, but below clipping.
Use slow AGC to reduce AGC distortion.

Analog diode or SDR envelope (standard) AM detectors have VERY POOR performance on fading AM signals. Don’t use them!!!

Even some PLL AM Sync demodulators can have poor performance during fading. Well designed AM Sync detectors stay locked even during signal fades.

PROBLEMS THAT CAN PREVENT A DECODE:

Noise: A high noise level can prevent Ham-DRM modes from demodulating correctly.
Timebase errors: An unstable sample clock or timing/data glitches will break the Ham-DRM lock, and it will need to re-sync. This causes data loss.
Distortion: Audio clipping or severe AGC or AM detector distortion will degrade the Ham-DRM SNR and may cause it to lose lock.
These problems can also degrade analog decoding (MFSK text or images), so it is advisable to ensure the receiver system used does not suffer from them.

HAM-DRM ADVANTAGES

100% error-free text/html
No noise or multipath degradation of images
No image slant
Images and text on the same page using html

KNOWN ISSUES:EasyPal 07/OCT/2014 (beta) may appear to stop decoding after the first image, but it does keep saving files into the Autosave folder.WinDRM will try to open each image file as it saves. Turn this off in Setup->File Transfer->Show Received Files.