On 3/11/2013 5:54 AM, Rob wrote:
wrote:
Funny, last night my two RCC's both updated like they should. One is an
analog clock and runs at 8x speed to get the hour ahead. In the fall it
does this to go 11 hours ahead. Quite a sight! They both did the job,
but my PC didn't update until it had been on for awhile, without being
connected to the I'net.

In Europe we have DCF-77 which is at 77.5 kHz.
The trouble receiving it is similar to WWVB.
I have several clocks in the house but some of them have only very
weak sync. Also, to save battery they only sync once every 12 hours
or so. At DST change, they may display the wrong time for a couple
of days, especially the one in the kitchen. I need to relocate it
to a place where I know there is better signal.

Yes, noise can be a problem I understand. I am hoping to get the
bandwidth down much more than most receivers so the noise won't be so
big a factor. With a signal bandwidth of a handful of Hz, it should be
possible.


The problem is (harmonics of) switching power supplies here as well.
Once I had a big open-frame SMPS that I used to power my radio equipment
and that switched around 25 kHz. Under the right circumstances, the
3rd harmonic wiped away all DCF-77 receiving within 5 meters or so.
Old CRT computer monitors also were problematic.

I presume you have some specific needs, low power being among them,
to stay focussed on WWVB for your clock sync. Most computer users
would use GPS now, or simply sync via the internet. GPS has a different
receiving conditions problem, but at least it isn't so much affected
by prominently present local interference.

Yes, this is actually a demo to illustrate how low power an FPGA can be.
An FPGA will run both the clock and the receiver and use power from
the environment rather than batteries.


Of course a GPS receiver requires a lot more power than a WWVB receiver,
although this has come down over the years. Using some sort of on/off
switching (syncing with the received time and then having it run free
for some time) may help a bit, the battery powered radio clocks do
that as well.

Yes, the receiver itself only has to run part of the time, 10% perhaps.
The clock has to run 100% obviously. Interesting enough, the FPGA has
a base power consumption (0 Hz) of nearly 50% of the power budget and I
am confident it will still make the goal.

--

Rick