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post #7 of Old 03-14-2013
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Re: Weatherfax audio file for testing

Originally Posted by RichH View Post
Oops sorry, dame bramage ... indeed most WeFax is broadcast on Upper Side Band (FSK).
I seem to be on a bit of a tear on vocabulary. Please forgive me. Skip the next paragraph if you don't care about what makes your radio work.

Frequency shift keying (FSK) is generated by a transmitter switching between two very close frequencies, usually 170 or 200 Hz apart, that are called 'mark' and 'space.' It was initially used for radio teletype (RTTY). Some genius (literally) applied to to image transmission and reception by setting standards for keying rates. It was intended to be received in a radio by injecting a signal at the frequency between mark and space and filtering the products with low pass and high pass filters to recover the mark and space. Another genius realized that this was analogous to SSB reception and that a couple of very narrow filters could recover the mark and space. Using an SSB mode (usually upper sideband, USB) means tuning off a bit (1900 Hz) in order to put the mark and space tones in the bandpass of the filters.

But you guys already knew that. *grin* It's pretty cool stuff, actually very simple and robust. Engineering elegance. I wish I knew the names of the geniuses because they deserve to be recognized.

Originally Posted by RichH View Post
Using a simple audio patch cord between the radio (simple portable 'Short Wave' with AM/USB/LSB/CW or HF/SSB) and a PC and using simple/fairly inexpensive programs will get you WeFax out at sea. I use a simple audio patch from my SSB (or portable SW receiver) into a Mac using "multi-mode" as the software for WeFax and marine TTY - MultiMode - CW RTTY SSTV FAX MORSE PSK31 ACARS SITOR AMTOR ALE DTMF FFT ASCII Decoding Software for the Macintosh
Right. A couple of points. One is that the mic input on MOST laptops is mono and the behavior of stereo plugs in mono jacks isn't always what is expected. Similarly, the way that mono signals (like SSB) are routed to stereo jacks as found on many shortwave radios is not consistent. I strongly suggest a 1/8" male mono plug to 1/8" male mono plug patch cord and a 1/8" female mono jack to 1/8" male stereo plug adapter. Put the adapter in the shortwave radio and hook up the patch cord.

There are a number of software options for Windows: JVCOMM32, Multipsk, and Digipan among others. I usually use JVCOMM32 on delivery. It is simpler and easier to set up. I do use Multipsk on Auspicious as it gives me the ability to transmit radiofax as well as receive.

sail fast and eat well, dave S/V Auspicious

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Last edited by SVAuspicious; 03-14-2013 at 08:18 AM.
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