GPS-sync'd NTP

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TeeJayHoward

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Feb 12, 2013
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I used to spend hours looking at the equipment used for satellite ground control on ebay. I always told myself that someday I'd have a setup like that. I wanted the Cesium beam clock, the GPS time dohickey, and all of those sexy BNC connectors. Well, we got on the topic of satellites today at work, and I decided to check out what a 1U GPS unit costs these days. A led to B, which led to C, which ended up with me buying a $75 PCIe GPS time card off eBay. I figure, my rack's already full. I've already got an NTP server. Why not just improve the accuracy of said server instead of adding another 1U that I don't have room for - Isn't that why I have a rack? For density?



I realized, of course, AFTER I made the purchase that I have no idea what kind of antenna I need for this card. The manufacturer's site states that I need a "remote powered GPS antenna/converter unit, up to 300m distance to antenna with RG58". Now, obviously, I could go looking for Meinberg's GPSANT model antenna, but given how expensive this stuff is generally when new, I'd rather not. From what I can gather, the "remote powered" part of the description means that the antenna is powered by the card. Why an antenna would need power is beyond me. In my mind, an antenna is just a fancy chunk of cable. The manufacturer's page for the supported model suggest that it converts the frequency of the signal so that it works with the RG58 cable. Do all GPS antennas do this, or do I need to buy a special one?

And I'm sure someone's going to ask why I need that kind of accuracy. I don't. It's just really freaking cool.
 

mstone

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Mar 11, 2015
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A powered antenna amplifies the signal in the cable for greater distance. Its normal when receiving a weak gps signal with equipment buried deep in a building.
 
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TeeJayHoward

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A powered antenna amplifies the signal in the cable for greater distance. Its normal when receiving a weak gps signal with equipment buried deep in a building.
Can you recommend an antenna/converter combo that would work with this card?
 

epimetheus

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Jan 15, 2013
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Satellite clock and antenna: {{pageData.title}}

Satellite Clock w/ NTP server (antenna separate): {{pageData.title}}

I design GPS clock systems for electrical substations quite often. If the card you show above can receive IRIG-B, PPS, 1kPPS, etc. then the SEL-2401 might be enough. It's available for purchase directly through SEL's website.
 
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TeeJayHoward

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Feb 12, 2013
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Satellite clock and antenna: {{pageData.title}}

Satellite Clock w/ NTP server (antenna separate): {{pageData.title}}

I design GPS clock systems for electrical substations quite often. If the card you show above can receive IRIG-B, PPS, 1kPPS, etc. then the SEL-2401 might be enough. It's available for purchase directly through SEL's website.
The card IS a "GPS clock." It's a Meinberg GPS170PEX. From the manufacturer's site:
It can be used as a stratum 0 reference time source for NTP and transforms any machine into a Stratum 1 NTP server without consuming additional physical space in your server room.
Wiring for this card is shown here, taken from the manual:

I should just need the antenna. (And hopefully I don't need to spend $500 for accessories on a $75 card!)
 
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TeeJayHoward

Active Member
Feb 12, 2013
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Found this detail about the antenna it's supposed to come with in the manual. Maybe it'll help someone recommend one to me?

 

TeeJayHoward

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Feb 12, 2013
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New antenna - $725
Surge protector for antenna - $230

Card MSRP: $2435

Looks like I'll be trawling eBay for a while. Meinberg also reiterated that a standard antenna will not work. Their GPSANT downconverts to 35MHz.
 
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T_Minus

Build. Break. Fix. Repeat
Feb 15, 2015
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Satellite clock and antenna: {{pageData.title}}

Satellite Clock w/ NTP server (antenna separate): {{pageData.title}}

I design GPS clock systems for electrical substations quite often. If the card you show above can receive IRIG-B, PPS, 1kPPS, etc. then the SEL-2401 might be enough. It's available for purchase directly through SEL's website.
Is the main reason / benefit of a GPS clock accuracy ?
 

epimetheus

New Member
Jan 15, 2013
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We use it in electrical substations to be able to sync events across the electrical grid. When there's a fault on the electrical system, modern protective relay generate event reports that record the conditions of the grid pre and post fault. This is important for fault analysis. It's critical that the event reports from multiple substations on the grid and synced with each other. Otherwise you can't make heads or tails of the data. We use a GPS clock at each substation to sync all the relays.