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Experimenting with Weatherfax - Shortwave (ongoing post)

A project log for (me) Learning to speak SDR

I recently purchased an RTL-SDR from NOOELEC and started fiddling around with it. This is my documentation of what works and what doesn't.

Timo BirnscheinTimo Birnschein 05/09/2021 at 03:540 Comments

The actual reason why I wanted to get into SDR was weatherfax. At some point in my life, I want to go cruising on a sail boat. To be able to receive current weather information without spending a fortune on satellite internet one would use weatherfax. Weatherax is a free service provided world wide to people with a shortwave radio and either an actual weatherfax machine or a piece of software to decode the data stream.

The primary issue with weatherfax, or shortwave rather, is that it requires a really long antenna. The frequencies range from about 5 Mhz to  17 Mhz with a useful center around 10 Mhz. To receive this reasonably well without spending a roll of $$$ on a professional antenna, you would need either a full wave antenna (~46 feet or ~14 meters) or a half wave antenna (~23 feet or ~7 meters). That's quite a substantial length when it is required to be vertical.

There are some active antennas that seem to bend radio waves to their will and can therefore be very compact but those usually suffer from lower reception quality. 

Some sailors use an insulated backstay as an antenna because it goes all the way up the mast. That works well, but is quite costly. 

My problem is, that I do not have a mast on my power boat, so all that's left for me is to experiment a little on a day by day basis and ask people if I may use their spare halyard to run a 23' cable up their mast for a few minutes.

This video gives a nice overview of what's involved when no SDR is used.

This video shows how to use an active mini whip antenna with an SDR. I'm actually surprised that this works at all. The Amazon reviews for this antenna are quite terrible.

This video goes into detail on using different software packages to decode weatherfax.

Next steps for me is to get a long piece of wire of at least 23 feet in length and somehow plug it into my HamItUp converter (essentially multiplies the frequencies from shortware into something my RTL-SDR can easily work with) and get someone in my harbor to allow me to run it up their mast. 

This seems to be an antenna people have success with, depending on their location.

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