Receiving radio faxes and other digital transmissions using a conventional receiver and computer
One of the unsuccessful radio
faxes What is the word “fax” usually associated with? Most will present a hybrid of a printer and a phone, with the help of which they transfer documents to distant corners of the planet. But did you know that sailors use faxes in the absence of the Internet? By fax, the Japanese news agency Kyodo transmits news in two languages, and various weather centers broadcast the weather a few days in advance. And we, too, can get all this and decode it - you only need a computer and a suitable receiver.
To at least take something, you need:
- HF receiver
- A computer
- Software for decoding
But first things first.
Everything is relatively simple here. I use the well-known Degen DE1103, but you can also try RTLSDR using software such as Virtual Audio Cable to drive the sound into the decoder. I think there is no need to explain that the receiver should have at least a headphone jack (or better, a line-out, as on DE1103) - otherwise it will simply not be connected. SSB support required.
The most important part - without a good antenna to catch a weak signal from a distant radio station is unrealistic. The simplest option is a long wire 1/4 of the wavelength. I use the standard antenna that came with my receiver, and in the city I get far from the best reception, and the KDPV is proof of this: because of the noise, it is simply unrealistic to parse many characters. Here there is good material for making a normal antenna.
Bad photo of a good antenna
The requirements are simple: having a sound card. The built-in is suitable in most cases, if there is an external, it is generally excellent.
There are many programs for decoding a WEFAX signal: SeaTTY, MultiPSK, Fldigi and some others. I recommend using Fldigi because of its free and versatility: in addition to faxes, it can decode almost all types of digital communications, as well as work on transmission (which, incidentally, MultiPSK can).
So how do I get a fax on the radio?
First you need to prepare the computer. To do this, download and install Fldigi. At the first start, he will ask for the callsign and more - you can safely skip this. After that, select the fax mode - to do this, select Op Mode> WEFAX> WEFAX-IOC576 or WEFAX-IOC288 from the top, depending on the station mode. After that, we connect the microphone input to the radio output, after lowering the volume on the receiver to a minimum. A "waterfall" should appear below. Switch the receiver to SSB mode (more precisely, USB).
Now you need to find the transmission frequency. The current list is published here (pdf) , herethere is a more understandable list. Pay attention to numbers like 120/576 - they indicate the WEFAX-IOC576 mode, 120 LPM (lines per minute). To begin, I recommend the frequency of 13883KHz - there is a round-the-clock transmission from Hamburg (in USB mode, you need to configure a little lower - I have ~ 13881KHz).
After that, we tune the receiver to the desired frequency, and in most cases fldigi will do everything for you - a rhythmic transmission sound will be heard, and a decoded picture will appear in the upper window. If you can see from the “waterfall” that the program has tuned somewhere in the wrong place, at the bottom of the window there is an AFC (Automatic Frequency Correction) button - turn it off, then “manually” tune the program to the frequency by clicking on the signal on the graph. If the picture looks skewed - use the Slant field to set the value at which the picture looks straight.
If there is silence on the frequency, then try later, when there will be a good passage. It is best to receive a fax at night.
Just in case - a video of the reception process:
Under the spoiler are some other faxes, such as Kyodo News.
Caution Bed Sheet
Kyodo News, goughlui.com
Kyodo News, goughlui.com
Using fldigi, you can also decode amateur messages transmitted in digital bands, which are usually lower than voice frequencies. To do this, just select the appropriate mode in Op Mode.
About upconverters for RTLSDR
UPD: As Comrade Antex noted , people without receivers can use WebSDR by wrapping sound through Virtual Audio Cable.
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