Hi Rud. I do not know any program, that introduces errors into bit stream for protocol tuning purposes. For tuning the decoders in PocketDigi, I used Moe's WSCGen, which generates test streams of various levels of AWGN.
http://www.moetronix.com/ae4jy/projects.htm It is not valid to simulate AWGN in bit stream by flipping bits. All the advanced decoders use "soft" bits technique, that works with fuzzy bits. For example, MFSK16 decoder utilizing Viterbi decoder implemented by Phil Karn KA9Q and used by gMFSK, fldigi and PocketDigi reads bits quantized to 8 bits, 0 signalizing 100% zero, 255 siganlizing 100% one and 127 dont't know. Noise may influence not only data stream, but also its synchronization in time and frequency (AFC). At the end, one needs to evaluate the whole decoder chain at once. One phase error in differential system (psk31, domino) caused by noise may introduce two successive bit errors. One error in FSK system will introduce only one bit error. > Fading: is it valid to simulate fading by removing some bits in the data > stream? It depends on the coding and synchronization. If the code is synchronous and sync lock is slow, it may survive the fading gap. Then you will get a correct number of bits, which will contain rubbish. An asynchronous decoder like RTTY will soon be lost, throwing away whole 6-bit symbols. 73, Vojtech
