Hi
On Jun 19, 2013, at 1:47 AM, Burt I. Weiner <b...@att.net> wrote: > One thing to keep in mind about modulating with a square wave is that you can > generate wide spread sidebands, so I'd give some thought to rounding it off a > bit. But then the chips were talking about, and some are Schmitt Triggers, > will change pretty fast and steep. I suspect in the remodulator it's not > much of a problem, if at all. > The modulation is at a 1Hz sort of rate, sidebands aren't going to be quite the issue they might be. If you increase the cost of the device 100X you could indeed solve the problem. > With regards to periods of Diurnal shift, it can get pretty wild in amplitude > variations, and phase can flip all over due to reflections as the big mirror > in the sky changes. Diurnal shift starts to get bad about two hours before > local sunset and again, not so bad before sunrise, and again for a while > after sunrise. Supposedly WWVB reception is supposed to be best when it's > all daylight between the WWVB transmitter and the receiver. I've always > found the WWVB signal to be more stable at night. Since the receiver works best when the daily shift is missing, there's no need to duplicate it with the remodulator. > > Someone mentioned that the receiver will not track if the remodulator is as > little as 1 Hz (cycle) of frequency. My 8170 has a crystal filter in the > preamp, so I would imagine it would be extremely selective. I think most, if > not all, of the WWVB clocks have crystal filters. The other day when I > ordered my crystals I had a choice of 60 kHz, 60.002 kHz, 60.005 kHz and > 60.000 kHz. The 60.002 and 60.005 were only available in Hugh quantity > purchases. The 60.000 kHz was a little more expensive but I bought 10 of the > little buggers anyway. I'll see how close they are when I build the > remodulator. Right now I've got some revenue generating work on the bench > that I need to get out of the way before getting back into the fun stuff, but > it shouldn't be too long. At 60 KHz, one ppm is 0.06 Hz. You are ~ 18 ppm off at 1 Hz. That's probably further than the VCXO in the Spectracom can track. The front end filter is likely > 10 Hz wide. Bob > > Burt, K6OQK > > >> Subject: Re: [time-nuts] WWVB remodulator for the Spectracom 8170... >> >> Interesting the HC will work all the way down to 2.2V so everything can be >> run from 3 Volts. >> No idea as to the effect of the xtal oscillator maybe the 3.9 M R needs to >> be changed. >> It also appears that the HC chip may doing the lions share of current >> consumption. Spec sheet says up to 20 Ma. Hard to believe actually. >> As for driving lengths of wire over distance it needs to be a buffer chip. >> 74hc244. But that seems like serious overkill it can drive 20 ma per port. >> Maybe a cd 4049... >> >> >> On Tue, Jun 18, 2013 at 6:41 AM, Bob Camp <li...@rtty.us> wrote: >> >> > Hi >> > >> > I don't know of any phase tracking receiver that would be bothered by the >> > modulator in Paul's schematic. You could implement it a couple of ways, but >> > the net result would be the same. The AM is a bit more square wave than >> > the WWVB signal. Modulation depth and timing would / could be dead on. >> > >> snipped... >> > > >> > > That is standard for most Costas loops with an I arm... haven't >> > > looked at his schematics carefully yet... possibly one might need some >> > > kind of AGC to use it as input to a second double balanced mixer >> > > serving as modulator in order to get the right 14 (?) db AM as signal >> > > fades slowly. Not sure how deep the diurnal fades are... > > > > Burt I. Weiner Associates > Broadcast Technical Services > Glendale, California U.S.A. > b...@att.net > www.biwa.cc > K6OQK > _______________________________________________ > 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. _______________________________________________ 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.
