Hi A few basics:
1) GPS receivers really can’t / don’t do a lot about multipath. The newer devices with a lot of correlators help a bit, but that’s about it. Simply put - newer is better. 2) Because of near the omnidirectional nature of GPS, antennas don’t do a lot for multipath. They can help a bit on low angle stuff, but that’s not going to be your problem. 3) Unless you can reasonably expect 4 sat’s in view at all time, don’t bother with setting up a GPS timing system. It will just make you angry with all the issues. A USB GPS on your PC will give you a pretty good idea of what you can or can’t pick up. 4) If the sole reason to do this is for NTP, consider simply setting up a local server and doing sync over your internet connection. Much less fuss …. Bob > On Nov 30, 2016, at 4:11 PM, MLewis <[email protected]> wrote: > > (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 > > _______________________________________________ > time-nuts mailing list -- [email protected] > To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts > and follow the instructions there. _______________________________________________ time-nuts mailing list -- [email protected] To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts and follow the instructions there.
