This illustrates a process lost to many building data demods. There is no need in many cases to be a hurry to get the from the front door to the back door of a process. Iterative processing of the demodulation process, each step making a best but poor estimate, and the reprocessing the stream using the results of previous passes to improve the demodulation accuracy. Lester B Veenstra MØYCM K1YCM W8YCM lester@veenstras.com US Postal Address: 5 Shrine Club Drive HC84 Box 89C Keyser WV 26726 GPS: 39.33675 N 78.9823527 W Telephones: Home:      +1-304-289-6057 US cell +1-304-790-9192 Guam Cell: +1-671-929-8141 Jamaica:  +1-876-352-7504    This e-mail and any documents attached hereto contain confidential or privileged information. The information is intended to be for use only by the individual or entity to whom they are addressed. If you are not the intended recipient or the person responsible for delivering the e-mail to the intended recipient, be aware that any disclosure, copying, distribution or use of the contents of this e-mail or any documents attached hereto is prohibited. -----Original Message----- From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On Behalf Of Jim Lux Sent: 27 September 2012 18:26 To: time-nuts@febo.com Subject: Re: [time-nuts] WWVB PM Receiver On 9/27/12 7:23 AM, J. Forster wrote: > Jim, > > What you are suggesting is essentially a spread spectrum system where the > chip pattern is time varient. > > IMO, this is an incredible kludge. And, there is no gurantee that the > algorythm for generating the chip pattern will not change down the road. > I think I poorly explained what I was thinking. Store the raw samples Run the samples through a demodulator to recover the bits using whatever technique works best: for instance, you can make your symbol transition decisions based on many bits at once, as opposed to only those you have already seen. Then, take those decoded bits and use them in a second pass through the data to remove the bits (sort of like the inphase arm in a Costas loop) so you can get a "carrier only" version of the input signal (with some noise at the symbol boundaries, most likely). Excise the transitions where the SNR is lower. Then, do your carrier frequency and phase recovery on what's left over. There's probably some elegant approach to deciding what to excise and what not to. But, in any case, no a priori knowledge of the bits is needed. (We did something like this at JPL to recover telemetry bits from Phoenix coming out of the plasma on EDL. Recover the carrier and symbol timing when you're farther down and then run the demodulator backwards in time). It's always easier to track than to acquire, after all, so why not acquire later when the signal is strong, and track backwards to where the signal is weak. _______________________________________________ time-nuts mailing list -- time-nuts@febo.com To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.