[ntp:questions] Re: PPS from TrueTime 468-DC GOES Time Receiver (with GPS antenna)
paul at thesimonet.org
Fri Aug 25 20:47:15 UTC 2006
Thank you for responding. Please excuse me while I learn to work with
this interface. My comments are interspersed below:
Hal Murray wrote:
> In article <1156450631.842127.105780 at 74g2000cwt.googlegroups.com>,
> "simonpg" <paul at thesimonet.org> writes:
> >So I have this fine receiver and have been a member of pool.ntp.org for
> >several years.
> Have you found the web page for the driver?
> (That may not be the latest one, it's just what google found for me.)
I guess I didn't make myself clear enough. The clock works great:
remote refid st t when poll reach delay offset
*TRUETIME(0) .TRUE. 0 l 29 64 377 0.000 1.233
-clepsydra.dec.c .GPS. 1 u 504 1024 377 56.294 16.420
-clock.xmission. .GPS. 1 u 567 1024 377 81.726 15.580
+bigben.cac.wash .USNO. 1 u 553 1024 377 46.023 15.031
-time-nw.nist.go .ACTS. 1 u 566 1024 377 36.026 20.802
+clock.sjc.he.ne .CDMA. 1 u 509 1024 377 54.394 15.218
LOCAL(0) .LOCL. 10 l 35 64 377 0.000 0.000
> Lots of info here:
> That doesn't mention a PPS signal. It says the signal is 468 MHz
> so I wouldn't be surprised if a GPS antenna filtered that out.
Yup, it does, "4-5 A phase locked receiver is used to receive and
recover raw data from the satellite signal. The raw data is processed
by analog circuitry and then passed to a microprocessor for conversion
to useful outputs; among which are a visual display, one Hertz and one
kilo Hertz timing pulses." It's just a little hidden.
> The usual approach with a PPS signal is to connect it to
> one of the RS-232 modem control signals. (I forget which one, but
> it should be easy to find.) Most of the PPS signals are TTL levels
DCD (Data Carrier Detect)
> rather than RS-232. If you want to get fancy you can wire up a
> level converter (MAX-232) type chip but it will almost-for-sure
> work with a direct connection. You do have to get the inversion
> right though - MAX-232 type chips are inverters. Software can
> normaly use either.
So, both the 1 and the 1K Hz pulses are available in the form of a BNC
connector. I know that TTL stands for Transistor To Transistor Logic,
but I don't know if that looks like a BNC connector.
> Once you get the signal into your box, try the ATOM (aka PPS) driver.
> Is GEOS still working? I found this note from June 2005 saying it
> was going off the air:
I guess GOES is indeed dead, but we have GPS now. Truetime came out
with a replacement antenna that converted the GPS signal to something
that makes the 486-DC happy, so I am happy.
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