On Sun, 25 Feb 2007 09:52:55 -0600, you wrote: >Angus wrote: >> Although that's not what I was talking about doing above, I think that >> it's pretty much what some of the hardware GPSDO's actually do using >> various types of oscillators (and to good effect too). As in these: >> >> http://www.jrmiller.demon.co.uk/projects/ministd/frqstd.htm >> http://www.frars.org.uk/cgi-bin/render.pl?parameter=&pageid=1285 >> >> the loop filter is basically just an RC circuit. It's not quite raw >> GPS, but is quite different to using a digital filter as used in a >> Thunderbolt, Shera, etc., which can run to hours. >> >> When the N1JEZ board was mentioned, I assumed that it was this type of >> controller that was meant - and I think it does need 10KHz unless it >> gets much more of a mod than a couple of counters. >> >> Angus. >> >Angus, > >Don't get me wrong, the James Miller design does a great job, >considering it's simple and elegant implementation and the fact that for >so little money you can have a frequency standard that beats anything a >ham could make in his or her shop. > >This will do a great job for most applications where you want to be >within a few Hz or so around 10 GHz, and as long as the GPS signals are >good. For the intended market, if the GPS signals are not good, you >simply wait or move the antenna. > >A lot of the money spent on commercial GPSDO's is spent on improving >hold-over performance, because many commercial applications simply >cannot postpone using the system until the GPS signal is good. > >I just wanted to point out that the 10 kHz output can be misleading. The >GPS timing is such that if you have a quality OCXO, a loop faster than >at least 20 minutes will actually do a disservice to the OCXO, >regardless of the PLL reference frequency. If you use an inexpensive, >not temperature stabilized VCXO, you can probably speed up the loop >quite a bit, simply because the VCXO itself in free running mode will >not be doing that great. > >If your frequency and time needs are modest (and that probably covers >99% of applications, including anything I could dream of personally), >this design will be perfectly satisfactory. > >But, and this is a significant caveat, this is TIME-NUTS where most >people are looking at that like the holly grail 1% :-) > >Didier
Hi Didier, Sorry, my original post was not very clear - I had only wondered if faster PPS signals might ever help with the measurement each second; I didn't mean to suggest that they might affect the required overall loop time much. ( Thinking back to all the posts a couple of months ago, I should probably resist any urge to comment on the effect of sawteeth on stability for the moment... ) Anyway, I was just curious. It's one of the many things I don't have much time to mess with, so wondered if anyone else had - but apparently not. Angus. _______________________________________________ time-nuts mailing list time-nuts@febo.com https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts