Re: [V4Protocol] V4 vs ALE400
- Glenn,Well there are always a tradeoffs of speed, bandwidth and robustness...goes back to Shannon’s theorm I think. (Part of what I sometimes refer to the “no free lunch” theorem!). In general FSK is better for robustness than PSK especially in poor multipath channels. The idea I have with CHIRP is it is like FSK but the tone continuously changes (chirps) throughout the symbol so it is more immune to selective fading which can wipe out a particular single frequency FSK carrier like is used in V4, Pactor 1, Olivia etc. Chirp has been used extensively in some radars and Sonar but is generally wider bandwidth there of course.In properly written DSP code amplitudes (if used) are generally ratioed during demodulation so absolute levels are not that important provided they don’t saturate the sound card. We are generally working with fairly weak signals (often 20 db S/N or less ) so the full range of a 16 bit A-D (about 90 dB) is not usually used provided the radio has AGC.Still much too early to know how effective narrow band CHIRP will be for keyboard text (I’m targeting something > 40 words per minute in < 500 Hz) but at least I’ll probably learn something along the way!!!
Rick KN6KBHello Rick,
It was during fading that the V4 program did better, and for some reason and I do not know why, the V4 program was running about 2 s units stronger on peaks. Maybe due to a more concentrated audio response from the soundcard?
It isn't often anymore where we all are experencing good band conditions, so any mode that can print at 100% and not crawl along is a plus. I always liked Olivia because it performed well, but it is very slow and if I used a different configuration to speed things up some, I would lose data. I enjoy the speed of V4 because I am not a fast typist and I don't feel as if I'm being chased by a wide boar trying to keep up with the buffer. Thanks for a great program.
Very 73, Glenn WB2LMV
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I know that most who have read your post about the Chirp mode will be anxiously awaiting it's release! Me too! I know that as a digital mode operator I am always looking for the mode that can print signals which are way below the noise level. JT65 and WSPR prove that it can be done, but those are not good for chats, so there is always that trade off. (-= I also like the modes that are not too wide, with all the different modes, and we each have a favorite, we really need to be able to share the little bandwidth that we have without interfering with one another. PSK10 is VERY narrow but the throughput is VERY slow. So I'm ready when you are to start using the new Chirp!
Very 73, Glenn