HF Weather Fax

After about one week of effort we've finally cracked the mysteries of weather fax via HF radio. Stephen did most of the work. I mentioned one night about having started preliminary investigations on HF weather fax on the Internet and the next night Stephen, Brenda, and I were on the boat having our first attempt, using some free software that Stephen had downloaded and cabling that he had brought. I did a fast review and located a headphone outlet at the front of the HF radio, then figured out how to enter a frequency (which shows how unfamiliar I am with the HF radio). We used the Upper Side Band (USB) as directed. Our first attempts were dismal. Each line was being replicated about 8 times across the screen. We could just make out the tiny outlines of Australia.

The next night Stephen brought some better software. Instead of feeding the signal directly to the laptop he fed it to an external disc store so that he could replay it over and over again to "tweak" the software. The result was better: a full-sized fax but really fuzzy. He got the best result by using AM instead of FM modulation as directed, and by sticking to the published frequency instead of tuning 1.9 KHz lower as directed by various sources.

Last night as we were walking to the jetty for another try I clucked about how the consistent advice was to tune to 1.9KHz below the nominal frequency, and that we should set the software to FM rather than AM modulation. The it struck me that I had probably not tuned the antenna at that frequency. Stephen had assumed that antenna tuning was automatic. I turned on the radio, tuned to the required frequency (minus 1.9KHz), went to USB, then hit the "tune" button. The Kenwood antenna tuner started to clack, indicating that it was changing the length of the antenna. We figured that we were on to something. We started recording the 36-hour MSLP (Mean Sea Level Pressure) forecast at 1200 UTC, 2100 Perth time. We listened to the signal being recorded and even to our inexperienced ears it sounded very, very good; like a fax machine on the telephone. We then passed the signal to the software and the graph of the signal was superb: clear differentiation between the "white" signals at +400 Hz and the "black" signals at -400 Hz. By then we knew enough to recognize the phasing signal at the beginning of the transmission.

The result is in the attached file. If you look closely you will see the outline of Australia, with one High and one Low. There is a High over New Zealand (bottom right). The word "demo" is plastered all over it because we are using the software on a trial basis. I'll be "purchasing" it, although my understanding is that it is essentially freeware with a very nominal fee.

At this point we have the latest transmission schedule of every station around the planet. We will be in a position to get charts of MSLP isobars, wave heights, wind strength, etc from anywhere on the globe. Excuse me for feeling pretty good about this.

The following page of the Australian Bureau of Meteorology presents their services, frequencies, and a reference their schedule of transmission: http://www.bom.gov.au/marine/marine_weather_radio.shtml
Their schedule is at http://www.bom.gov.au/nmoc/rad_sch/
Some technical information is at http://www.bom.gov.au/marine/tech_voice_fax.shtml

On another front, I purchased a short "rubber" radio antenna and mounted it next to the cabinet holding the radio, next to the mast. The FM radio reception is outstanding. The AM radio reception sucks. We ran part of a movie on the laptop using Stephen's small black box that amplifies the weak headphone signal from the laptop before it is passed into the AUX1 input of the Pioneer sound system. The result was outstanding. As far as I am concerned, we now have a floating 12-volt poor man's entertainment centre.