Bob You missed nothing really. 100 Hz because thats what the NAA radio used with the tracor doubler. So when I moved it to wwvb that was the baseband signal. Now that said I liked the 1 second phase flips at 100 Hz delay. Dog slow and perfectly OK to resolve the phase flip and I can use my favored uproc.
Whats funny is that any crystal close to anything existed. Digikey says they have a 6.1Mhz xtal but when selected goes to 6.144 MHz. I was amazed that both mouser and digikey had the 5.9904 xtals and both stocked a variety of cases. Must be some story about whatever that frequency is. Did try lots of frequencies and divider math to come up with a simple LO scheme for 61 or 59 KHz. Messy. Regards Paul WB8TSL On Mon, Sep 22, 2014 at 7:42 PM, Bob Camp <[email protected]> wrote: > Hi > > Is it really that much harder to process a 1 KHz note out of a direct > conversion receiver than it is to process a 100 Hz note? > > Put another way - you already have a crystal filter in the front end of > the “radio” right? It will do a better job knocking down an “adjacent > channel” 2 KHz away than one 200 Hz away. Even without the crystal filter, > the only likely thing you are trying to reject is noise. Effectively the > “no filter” approach degrades your signal to noise by 3 to 6 db depending > on the type of noise you are dealing with. > > I’m asking because I may have missed something that makes 100 Hz “magic” …. > > Bob > > On Sep 22, 2014, at 6:15 PM, paul swed <[email protected]> wrote: > > > One of the methods suggested for working with the wwvb psk is down > > converting to a lower frequency. When experimenting with NAA I had built > a > > 24 Khz receiver that down converted that signal to a 100 Hz base band. > > It was a minor effort to shift it to 60 Khz by changing the LO. I liked > > what I saw. Essentially a simple direct conversion receiver with about 42 > > DB of gain. > > The PSK flips at every 1 second depending on the data and is 1/100Hz > > delayed from the wwvb flip due to the down conversion process. This makes > > the further processing very reasonable in just about any micro. > > But the LO is a mess. Not bad if you have an HP3335a as I did till last > > week. (Another project to repair) for 100 Hz the LO must be at 60.1 or > 59.9 > > Khz. Or synthesize it etc. Starting to get seriously ugly. > > Or jump to a 1 Khz with 59 or 61 KHz. But I hated the idea of mixers and > > filters. > > > > Any Time-Nuts seen those crystals or oscillators around lately? Seriously > > missing from the general haunts. > > > > But turns out and heavens knows why there are plentiful 5.9904 MHz xtals > > around. I ordered 5 from Mouser $ .46 ea. > > 5.9904/100 = 59.904 as a LO and suspect it can be moved to the correct > > frequency not that it has to be. > > Not sure there is a real need to lock the LO at all. > > So an exciting bit of news. > > Regards > > Paul > > WB8TSL > > _______________________________________________ > > 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. > _______________________________________________ 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.
