[time-nuts] PN sequence generation using GPS

[Magnus Danielson]

Bob,

On 02/16/2011 10:51 PM, Bob Camp wrote:
> 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.

It's actually not the prime-number aspects which is important, all 
Maximum Length Sequences (MLS) will not be prime-number lengths as not 
all Mersenne numbers is primes, and then non-prime polynomial lengths 
like 10 naturally breaks up (1023 = 31*33).

The key factor is that the sequences does not line due to lack of common 
factors. However, this deficiency can be overcome by shortening the 
sequence.

> 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.

Probably more trouble than it is worth it.

Cheers,
Magnus