100011010 should become 1 0 0 0 1 1 0 1 0 space-space,mark-mark,space-space,mark-mark-mark-mark,space-space-mark,space
with the arbitrary decision on the first bit, that could be either space or mark, as there is no previous state. space is 1200Hz and mark is 2200Hz. I have already encoded this on a DDS based on PWM on a PIC 16F628, but I had control over REAL time there. I have just written a block to do the differential encoding, that is, to obtain the correct -1,1 sequence, but my doubt is how to apply this to the freq modulator in order to obtain exactly the two tones I need for mark and space, and the correct bit timing, as I do not have control over time... MC > Bel 202 does NOT use Manchester encoding. The individual bits are NOT > sent bilevel but opposite polarity. Bel 202 very much as energy at DC > after demodulation which Manchester would eliminate. It does have > differential encoding but that is not Manchester. > > 100011010..... > would be transmitted as > ?10010111.... > > This is nothing to do with biphase elements. > > > Bob > > > > Matteo Campanella wrote: >> bell 202 coding requires to send a steady tone (mark or space depending >> on >> the previous state) on 1 and a tone change on 0, so the tone change must >> happen in the middle of a bit. >> >> in order to use a modulator I guess I should use a block to get a >> sequence >> of symbols that is twice as long as the bit sequence, that should be >> "played" twice as fast as the bit stream sequence, where bits at zero >> are >> represented by 1,-1 (or -1,1) and bits at one are represented by -1,-1 >> (or >> 1,1). >> >> is there any way to do that by using an already made block? >> >> Matteo >> >> >>> On Tue, Mar 28, 2006 at 11:51:03PM +0200, Matteo Campanella wrote: >>> >>>> Hello, I am trying to find the best way to implement a bell 202 modem >>>> in >>>> gnuradio. The problem I am facing is that I need to produce two tones, >>>> one >>>> for mark and one for space, and I have to switch from one to other >>>> depending on which symbol I am sending. The duration of the tone (or >>>> tone >>>> switch) must be set exactly according to the baud rate of 1200 I have >>>> to >>>> produce. >>>> >>>> I was thinking to use the nco class to generate the tones, and to >>>> output >>>> n >>>> samples per symbol at a certain fixed sample rate that would be enough >>>> for >>>> the 1200 baud, let´s say the standard audio 48000. >>>> >>>> Has anyone better suggestions to work this out? >>>> >>>> MC >>>> >>> Use the gr.frequency_modulator_fc block to generate complex baseband >>> FSK. >>> >>> You'll probably want to use gr.bytes_to_syms to in front of it, or in >>> the more general case: gr.packed_to_unpacked followed by >>> gr_chunks_to_symbols_bf. >>> >>> Eric >>> >>> >>> >> >> >> >> >> _______________________________________________ >> Discuss-gnuradio mailing list >> [email protected] >> http://lists.gnu.org/mailman/listinfo/discuss-gnuradio >> >> > > > -- > AMSAT VP Engineering. Member: ARRL, AMSAT-DL, TAPR, Packrats, > NJQRP/AMQRP, QRP ARCI, QCWA, FRC. ARRL SDR Wrk Grp Chairman > Laziness is the number one inspiration for ingenuity. Guilty as charged! > > > _______________________________________________ Discuss-gnuradio mailing list [email protected] http://lists.gnu.org/mailman/listinfo/discuss-gnuradio
