Weather Fax (HF-Fax)

coastguard-boston-sept152015-1 Figure 1: Received from Boston Coast Guard Transmitter (4 kilowatts) with the fldigi ham software.

The received transmission was not very strong, so the resulting facsimile came through with some rough spots, and the bottom half is relatively poor, but it should be observed that good results are possible.

hurricaneforecast1 Figure 2: A developing storm in the Atlantic is detailed here, in another fax from the same coast guard transmitter (Boston) on Sept 15, 2015.

The weather fax signal picked up strength on the second transmission, and the increased detail is evident in the resulting fax, shown in figure 2. It was transmitted sideways, which is why the lines appear at right angles to what’s expected.

comp6 Figure 3: waterfall display of fldigi software, with various signals for comparison

For comparison purposes, the graphic (shown above) illustrates the waterfall display of the fldigi software when it’s showing a 1) strong AM broadcast station, 2) a weaker AM broadcast station, 3) a weak HF weatherfax signal, and 4) four BPSK31 signals of varying strengths.

I like to use BPSK31 signals to tweak my gain controls, and to verify that the cables and antennas are indeed plugged into their respective connectors! Broadcast AM signals work for this purpose too, and are plentiful on the short and long wave frequencies. The AM broadcasters use much more power, on average, than the HF weather fax broadcasters (50 kilowatts++ versus about 4-10 kilowatts), and are much more numerous than the latter. “Tuning” up and down the bands, one can snag AM broadcast stations easily. You’d almost never find a RadioFax weather station that way. The terms RadioFax and HF-Fax are sometimes used interchangeably, even though there are RadioFax broadcast stations to be found on medium and low frequency bands. Because RadioFax signals are harder to find than AM broadcast stations, we use advertised frequency lists kept by various governments, sometimes published on government sites.

I’ve had some success with the FlDigi software, using it to receive weather faxes that are quite readable. The FlDigi software is capable of displaying weather faxes in a self contained way; nothing else is needed except a shortwave receiver and a computer with a sound card (with some means to connect the two while keeping impedances and levels in line.

RadioFax is a type of weather fax that is commonly transmitted via frequencies from 122 KHz all the way up to about 17,000 KHz. There may be a few stations that use higher frequencies, but for some reason they are not numerous. RadioFax (sometimes called HF-Fax) is a different sort of thing than APT LEO satellite weather fax. This page deals with the former, while another page on this site contains some info about the latter. RadioFax is transmitted from terrestrial (ground) base broadcast stations. Using RadioFax, I get good results from Boston (12750 KHz), as well as New Orleans (4317.9 KHz), and Nova Scotia (4271 KHz). Boston transmits also on 4235 KHz. The NOAA publishes a list:

http://www.nws.noaa.gov/om/marine/rfax.pdf

chart-not-avail Figure 4: Odd message coming from a British weather fax broadcast station

Software:

The main page for the FlDigi software is:

www.w1hkj.com/

The download page for FlDigi software is:

www.w1hkj.com/download.html

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