[time-nuts] How do I know my GPS stabilized oscillator is working?

[Bill Hawkins]

I can give you a data point about lightning.

Last year, lightning hit a tree that was so close to my
neighbor's house that the deck roof had been cut back to
clear it. That tree was 20' below nearby trees, but it
had an unobstructed view of the pond behind us. Lightning
hit it (a spectacular flash-bang), split it, and jumped
into the house electrical system at the outdoor floodlight
socket on the deck roof.

My antenna mast is about 75' from his tree. There are two
HP GPS antennas mounted five feet apart on a 2" pipe tee
arrangement. A ground wire rises straight up from the ground
rod to 3' above the antennas. The antennas were not powered
at the time, but were connected to Z3801s with RG-8 cable.
The antenna closer to the strike is now junk. The other
antenna is good. Ah, the altitude of the antennas is the roof
line of the house, so that my wife won't be embarrassed.

Excuse my ignorance, but what is a "nice box" and what are
LPRO, UT+, TVB-DIV? A computer and programs I should know about?

Regards,
Bill Hawkins


-----Original Message-----
From: time-nuts-bounces at febo.com [mailto:time-nuts-bounces at febo.com] On
Behalf Of Glenn
Sent: Monday, July 31, 2006 8:52 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] How do I know my GPS stabilizedoscillatoris
working?

Tom Van Baak wrote:

>1PPS -- Lastly, there is one convention I found handy with 1 PPS 
>sources, specifically those GPS boards that are designed to suppress 
>the 1PPS signal when they loose lock. In this scenario make the 
>reliable 1PPS ref the start channel and the GPS 1PPS the stop channel. 
>If lock is ever lost -- your TI readings will reveal the number of 
>missing pulses.
>

That's a great idea. Thanks.

Here's the setup I'm working toward:
* Motorola Mag Mount GPS Antennta attached to our DISHtv dish
  (The dish makes a decent mount and the ant. stays stuck, even in storms!)
* 6m ant. cable down to a "nice box" in the bedroom w/LPRO, UT+, TVB-DIV and
interface board
* 3x ~30' coax down to the 5334A in the server closet
  * 1: 10 Mhz Ref. to 5334A ext. osc.
  * 2: 1 PPS from GPS to INPUT A
    * Since I'm testing the TVB-DIV and the UT+ doesn't shut off the 1 PPS,
this is the more reliable of the 1 PPS's.
  * 3: 1 PPS from the TVB-DIV
* 1 CAT5 cable, also down to the server closet, to the NTP server
  * GPS TX/RX
  * TVB-DIV STOP signal / 1 PPS (RS232 level)
  * +12V/GND
  * 1-wire interface (for temp. monitoring and a separate counter)
* GP-IB/USB adaptor from the 5334A to the NTP server.

This should allow me to measure time and freq. offset and drift.

What about a lightning arrestor on the GPS ant? The dish I'm mounting it on
is grounded, there is a tree ~10' taller than the dish ~20' to the NE, more
trees to the west, plus feeder power lines at about the same hieght to the
east. So, it's not a great place for antennas, but I think lightning is much
more likely to hit something other than the GPS ant. 
Although, "more likely" and what actually happens are often very different.
What are other people doing about this?

Any comments on this setup?

thanks,
glenn


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