Decoding data signals is a fascinating side of hobby radio and there is a good portion of this website dedicated to it, which is why we are always up for trying something new and when after a post about using MultiPsk software prompted one of our twitter followers (thanks Patrick) to forward a link to a program called Fldigi we decided to check it out.

Having come across Fldigi before but never getting around to installing it for some reason we were looking forward to trying it out.

Fldigi Overview

Fldigi is a cross platform free open-source radio signal decoder that uses a computers sound card as the source for data. This kind of decoder has been with us for a long time because the equipment and computer specifications needed to get a setup going can be low.

Able to decode most of the common data transmissions found on the HF and VHF/UHF bands (RTTY, CW, PSK etc) with a reasonably basic computer setup Fldigi can be a good starting point for those wishing to expand their radio hobby a bit further.

Test Equipment

To get a good measure of how this software runs compared to all the other programs we use it was setup on our normal data decoding computer with the same equipment as we always use consisting of DX394, Simple Interface and Dell base unit (Windows XP service pack 3, dual core 1.86Ghz/1GB ram). By going with what we usually use it provides a baseline performance between different programs and save us having to move stuff around to create a new radio setup 🙂


As with a lot of open-source projects the download page is nice and basic with clear links as to which package you should be using based on what operating system is installed on your computer. Actually getting the software into the computer was easy and quick with the only stumbling block being our 3rd party firewall stopping things half way through.

The firewall is wound up so tight that this isn’t unusual when it sees something new and we still remember a confusing afternoon when it took a dislike to a large part of the windows operating system (for reasons only the firewall knows) and put it in a sandbox.

The Interface

fldigi control interface

Fldigi Control Interface Decoding RTTY on 18.100 Mhz

When starting the program you are presented with a clean interface showing only the business parts of the decoder like the print out/TX  sections and the ever important waterfall. Instead of cluttering up the screen with countless buttons Fldigi has all the options neatly hidden away on simple drop down menus right at the top of the screen.

Logging Option

As with most programs there is a logging program included but what makes the one bundled with Fldigi different from some of the others is that it actually works well through a clean and fast customizable interface. So many times the logging part of radio decoding software seems more of an afterthought by the developers and we end up with something that borders on unusable.

The log databases can be easily exported in a format that’s compatible with other software and the sorting options once shifting through a big selection of data are good enough for most users.


First off the program hardly makes a dent in the resources of our data mode PC making it easy to run alongside web browsers and other programs.

With a handy signal to noise setting right below the waterfall we found less need to adjust the radios volume so often to get good results along with being able to selectively tune out other nearby stations using this feature.

Overall the software’s ability to give a half decent decode on even the faintest of signals makes it a winner in our eyes and its going to get a lot more use over the next few months.

A Small Problem and our Wishlist

Having had a few days to play with the Fldigi software we can safely say that overall its nicely put together and runs well on the test computer although the bedding in process was not without a problem.

Not Saving Settings

When you first start the decoder you are prompted to go through the configuration process to set Fldigi up the way you want it, this is easy enough and these settings can be revisited at any time but when restarting the program none of the changes we made were sticking? The problem was that we didn’t save the settings after the initial setup was finished (from the top menu click configure then click the save config right at the bottom of the drop down menu). This error would never have happened if only we had look at the manual first, but who does that right!


This programs performs so well across the data modes it decodes its a shame that SSTV isn’t an option on Fldigi. The way the software picks even the weakest signals out from the noise would definitely be a great benefit when dealing with SSTV, we can only hope that it will be added in future updates of the software.

Where to get Fldigi

If you fancy trying out Fldigi for yourself all the versions can be downloaded FREE from here and all the Fldigi documentaion here

If your trying out this software for the first time please drop us an email or use the comment box below to tell us how you go on.

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