EchoFilter – famous DSP!
I guess everyone will agree with me, that DSP (digital signal processing) meant a great benefit for radio amateurs. Today, even mid-range transceivers have built-in DSP as standard, it can be purchased as an internal module for cheaper ones, or a separate external device.
The third and cheapest (if you already have a suitable computer with a sound card) is to use some DSP program. The vast majority of these programs are oriented towards filtering the received signal. EchoFilter handles it all “left rear”, in addition, it also offers several superior functions. The biggest difference compared to similar programs is the implementation of functions for creating modulation, that is, of the transmitted signal.
Two versions of EchoFiltr are currently available, namely the freely distributable version 2.0 and a limited demo version 3.0. It can be upgraded to full by paying the registration fee 40 USD. You will need at least a P-200 with W95+ and a sound card to run the older version, the new version needs a P-II with 64MB RAM, W95+, sound card and SVGA (800×600). You will lose something over 1MB on the disk. On my K6-2/333 with 96MB RAM, both versions work without any problems, however, starting another program is already manifested by sound interruptions.
The main screen of the program is dominated by the spectrogram, on which we can see in real time the effect of the used functions on the processed signal and the signal level graph (force graph, plot). Control is “mouselike” – just click and select another type of filter from the menu, turn on AGC… Small bar diagrams inform about processor load and buffer usage.
Of course, the new version offers much more. AGC has been improved, which is continuously adjustable. Even the noise blanker is better.
The first of the functions usable for TX is the compressor. Its meaning is clear: limits peaks in the signal, which exceed the set level. You, as well as the amount of compression can be smoothly adjusted.
The second is the expander. This one works like this, that it amplifies the weaker parts of the signal, while stronger (tips) they remain unchanged. The resulting signal is softer and gives the impression of being large “puffiness” modulation. Both of these functions are of course also applicable to the received signal, but they are destined for TX.
The third is the equalizer. This allows the transmitted signal to be beautifully embellished exactly according to the operator's wishes. It is available 7 pull potentiometers.
The sound recorder allows you to save the received signal to disk. If we subsequently play it in the integrated sound player, we can re-apply arbitrary filters to it and thus later decipher even a seemingly completely unreadable signal.
The only disadvantage of this program is, that it is not free. The demo version is being worked on every day 5 minutes it blocks and it is necessary to start it again – but you will be held back by the initial screen, exactly 15 seconds. In addition, the spectrogram will only work 30 seconds (but you can usually get by without it) and the recorder will only allow you to record 10 second file…
But I think so, that EchoFilter by Luis Botha Sr. and Luis Botha Jr. in any version is an excellent program. You can download it in the DOWNLOAD section.
