[time-nuts] Truetime dc 468 goes sat rcvr simulator basics working

[paul swed]

Well I think this puts me in the dangerous zone of time nuttery.

I had posted to the group about a month ago about a Austron 2201 gps rcvr
and any documents anyone might have. Russell responded and sent me some
great documents on the Austron.

In a phone conversation with Russell we started talking about the old
Truetime dc 468s. Kind of got me thinking. I have been able to design a
small single chip goes timecode simulator to drive these older clocks.

The dc 468 was always quite attractive with their panelplex 7 segment
displays. Have re-purposed the boxes for several other projects on occasion
using the supply nd the displays.

I find the dc 468s at flea markets still for $5 in the northeast US.
Generally no converter assembly though it doesn't matter since the GOES
timecode signals been gone since 2005.

At the moment the software fits in a small parrallax SXB micro. Its written
in basic language and compiled. Runs very fast with a 20 Mhz clock.

At this stage the unit puts out a manchester encoded timecode signal and is
injected at the very first data stage on the decoder. You have to do this to
get the PLLs to lock so things decode correctly. I have not attached a GPS
time signal to it yet and associated time decoding to automatically sync the
clock. That will be the next item. But I suspect this will be a bit ugly.
Like sync once per day type of behavior.

Another interesting thing I discovered in this project. That the GOES 100 Hz
timecode actually transports a very stable frequency reference. So you need
a pretty good 100 hz source. What this means is the clock will only drift as
much as that source drifts. Thats why I think a single sync 1 time per day
is most likely just fine. Additionally the internal 10 MC clock locks to the
100 HZ and is pretty stable. (Ok now I am in trouble. What on earth does
that statement mean in this group?)

As with the Loran simulator I will share the information with the group as
it shapes up.
For now I need to make sure the basic software actually is correctly keeping
time.

Regards
Paul
WB8TSL