Hi According to the rules, you are not allowed to reset shift register other than by feedback during a transmission. In order for a reset to be "transparent" it would have to always happen at the same time. Usually that's when the register is full or empty.
A proper (MLS) PN sequence will be (2^m) -1 long. For the allowed ham sequences that would be 2^7 -1 = 127, 2^13 -1 = 8191, or 2^19 -1 = 524287. If they are not MLS then I'm off a bit. None of those divide into 10 MHz very well at all, since they all are prime numbers. If you use the shortest sequence, you would get to reset every 127 seconds with a simple approach. You likely would do better to run a bit more math and figure out the "right" sequence for the time you are at. Bob -----Original Message----- From: [email protected] [mailto:[email protected]] On Behalf Of Joe Leikhim Sent: Wednesday, February 16, 2011 4:14 PM To: [email protected] Subject: Re: [time-nuts] PN sequence generation using GPS For clarification; I am investigating an experiment using GPS to create a FHSS or DSSS project similar to those of AMRAD and described in the ARRL Spread Spectrum Sourcebook. In those experiments, a specific shift register sequence was used (see below), the clock was free running and a reset tone was transmitted on irregular intervals (whenever synch was believed to be lost) over the radio circuit. In my experiment I would like to derive the clock directly from a GPS at each radio and use the GPS to periodically reset the shift register without causing a glitch or disrupting the sequence. There is mention in the sourcebook of a relationship between clock speed, reset interval and shift register stage length. It is this area that I am confused. My question is: If I use a 1PPS derived reset interval, a 10 MHz clock and the PN sequence below, will the reset interval intrude on the sequence? If so, what reset interval or fraction of clock speed will be least disruptive? This is the example shift register PN sequence: "There is some common notation for PN sequence identification. The sequences are often generated by a shift-register using feedback. The PN identification notation indicates which bits are modulo-2 added and fed back to the input of the shift-register. As an example the [7,1] sequence is generated by modulo-2 adding register bits 1 and 7, inverting this and applying this to the input of the shift register." Thanks -- Joe Leikhim Leikhim and Associates Communications Consultants Oviedo, Florida www.Leikhim.com [email protected] 407-982-0446 WWW.LEIKHIM.COM _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
