[ntp:questions] Roof antenna, which one, would you bother?

William Unruh unruh at invalid.ca
Sat Mar 22 16:03:55 UTC 2014

On 2014-03-22, David Taylor <david-taylor at blueyonder.co.uk.invalid> wrote:
> On 03/01/2014 10:54, Ralph Aichinger wrote:
>> I am currently in the process of remodeling my house
>> and a dedicated outdoor/roof mounted GPS antenna
>> would be possible to mount without excessive cost.
>> I probably would not see a huge difference for
>> timing purposes, but what would your choice of
>> an outdoor GPS antenna/receiver be? I am planning
>> to put the NTP server (small Raspberry Pi, nothing
>> fancy) into a rack maybe 10 metres of cable length away
>> from the roof. Or would you move the NTP host itself
>> to the attic and run Ethernet up?
>> I suppose something like the Garmin GPS 17x (mast mount
>> GPS with serial output and PPS, intended for the marine
>> market) would work fine, also be robust enough and
>> cheap on the used market.
>> Would mounting just an antenna (active or passive) also
>> make sense, or would cable loss be too high?
>> What would *your* roof top setup be? Cost is of course
>> an important consideration, on the other hand, 100
>> or 200 Euros for the GPS, antenna and mounting hardware
>> is probably OK. I would prefer to do cabling jobs now,
>> while I am in the process of doing a lot of "dirty" things.
>> Or would you not bother at all, and just put some puck into
>> the window (which probably works too)?


At work I have a gps in an east facing window looking out at the sky
through a large Fir tree just outside the window. Sure gps receiver with
its very very cheap antenna. Works fine. Gives the right location to
within 3m (in time that would be 10ns) and the time. 
Ie, before I put the antenna into an inaccessible place (when it draps
out on you after a few years-- two of my Garmin 18 s died after three
years) I would test more accessible locations. 

>> TIA
>> /ralph
> I would try with the Raspberry Pi with a GPS with built-in antenna in 
> the attic, running an Ethernet/power lead up to the attic.  There are 
> some examples here:
>    http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html
> You can get a no-soldering GPS for the Raspberry Pi which includes the 
> u-blox 7Q receiver (TCXO and PPS) and an SMA socket for a puck or 
> outdoor antenna as described here:
>    http://www.satsignal.eu/ntp/Raspberry-Pi-NTP.html#no-soldering
> In my own setup, I have several of those magnetic puck antennas just 
> within a room on the top floor of a two storey building, and one Garmin 
> GPS 18x LVC sitting on the roof.  Lightning protection is not an issue here.

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