[time-nuts] Mounting GPS Antenna on Steel Roof

Stanley Reynolds stanley_reynolds at yahoo.com
Sun Mar 9 13:46:32 EDT 2008


"Why not use RS232? Several issues come into play. One is that driving long cable runs with large voltage swings slows down the transition. Another is that many receiver designs use slew rate limiting capacitors in an effort to reduce noise coupling. These capacitors of course introduce delays, that will also drift with temperature and the voltage of the drivers. Basically you are throwing away some amount of timing accuracy when using RS232 for the PPS signal. It is slightly more convenient to use RS232 to drive the PPS signal of course. " from web link www wraith sf ca us/ntp/#gps-receiver

They are using a modded RS232 board to bypass the RS232 chips. The PPS signal would be the one signal to most benefit this special treatment as far as time delay the serial signal would benefit from the increased distance. Maybe everything is one package ?

I know this thread is more about isolation/surge protection but the trade off is the more stuff we add the more chance for variable delay vs static delay, with the variable part adding to error. But the simple route with less stuff also has less too no protection. The antenna protection does protect the GPS receiver, but the first goal may be to keep the surge away from the inside of the building. Maybe a WiFi or Fiber link to the internal network with the network time server, separate power supply and GPS receiver all mounted outside ? Another reason to use a small embedded low power server. Layers of protection as to reduce the damage. Low power would also add solar / battery as an option which would remove the power source as an entry / exit point for any surge. 


----- Original Message ----
From: "GandalfG8 at aol.com" <GandalfG8 at aol.com>
To: time-nuts at febo.com
Sent: Saturday, March 8, 2008 8:32:29 AM
Subject: Re: [time-nuts] Mounting GPS Antenna on Steel Roof


In a message dated 08/03/2008 13:29:42 GMT Standard Time, didier at cox.net  
writes:

The  MAX232, like all RS-232 interface chips I have ever come across,  inverts
the signal.



--------------------
That'll explain it then:-)



  
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