[time-nuts] Best Chance GPS module

MLewis mlewis000 at rogers.com
Wed Nov 30 16:11:05 EST 2016


(resending as I tried posting in html...)

Hello,

I'm a novice at time issues. I've been gathering info and I think I'm 
ready to start asking questions.

I'm after a time solution for my personal computer. It looks like I need:

*    a standalone box to be my own local personal NTP server (so the 
variable processing load on my main box can no longer affect host 
polling software timestamps...)
*    run standard NTP Client & Host software on that box
*    discipline it with PPS from GPS, using an active antenna
*    use NTP to obtain the NTP time from this local personal NTP server 
as required
*    I don't know if I need two additional boxes: one for the NTP host 
and another for receiving the GPS PPS signal, like a Pi in kernal mode.

GPS issues.

*    I'm in a semi-basement apartment.
*    Building faces due South.
*    Building is 1960's brick & concrete, steel trusses & sheets in 
place from the concrete floor pours.
*    Windows from 14" to 38" from the ground. My antenna has to be 
between those.
*    Window frame is plastic retrofit over wood Pearson-sliders.
*    There is a bank of buildings due south of me that leaves me with 
clearance elevations between 6 and 12 degrees. I'm at 45.42 North.
*    Due South within what open sky I have, are two heights of 
electrical wires, around 35 feet out from the building at the edge of 
the parking lot.

I'm expecting multipath from: those buildings, my building and I assume 
the wires and possibly the cars?

Between the multipath and a less than full view of the sky, I believe 
I'm needing a GPS module:

*    that is sensitive,
*    good multipath handling,
*    GPS & GLONASS, to get as many sats possible out of the sky-view I have.

Due to my location difficulties, considering newer more sensitive GPS 
modules seems to make sense, even if they're not timing modules. I was 
tempted by a Qualtec L86 with -148|-165 dBm or a SkyTraq Venus838LPx-T. 
Then a ublox Max-M8Q with -165|-167 dBm & its stationary mode. But then 
I discovered I can get a ublox NEO-M8T with -165|-167 dBm sensitivity, 
its multipath handling and concurrent reception of GPS/QZSS, GLONASS, 
BeiDou & Galileo.

A ublox NEO-M8T with an active timing antenna (GPS | GLONASS ?) seems to 
be my best chance of being successful at my location.

Questions:

*    Is there a more suitable GPS module than the ublox NEO-M8T for my 
location issues?
*    Can anyone recommend an affordable suitable antenna for GPS & GLONASS?
*    One box or two, for running a local NTP host and receiving the PPS 
from a GPS module?
*    Is there a better solution for a micro board than a Rasp Pi with 
its USB controlled Ethernet, or the BBB with it's RF issues?
*    What am I not considering that could end up biting me?

Thanks,

Michael




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