On Wed, Oct 23, 2019 at 9:20 AM Martin Burnicki <martin.burni...@burnicki.net> wrote: > > shouldbe q931 wrote: > > I recently acquired a pair of Meinberg M600's (with GPS-CON downconverters). > > Just a summary of what it's for: > > Most Meinberg GPS receivers expect an input signal that has been > down-converted from the original L1 frequency. > > The appropriate Meinberg antennae have a built-in down-converter which > is DC-powered from the receiver, via the antenna cable. > > The GPS-CON is an external down-converter that expects an input signal > from a standard L1 antenna, and outputs a down-converted signal that is > appropriate for the receiver. > > The down-converter itself is powered by the receiver, just like the > original antenna. The DC power that can be applied to the GPS-CON is > only forwarded to the 3rd party antenna, whether a voltage is to be > applied depends on the antenna. > > > From the usual auction site got a dual band antenna (for > > futureproofing), a 2nd hand mini-circuits ZN4PD1-63W-S+, several SMA > > BIAS-TEE to prevent DC issues, and an assortment of coax cables to > > connect everything up. > > > > To power the antenna I used a ublox M8Q series without a BIAS-TEE > > connected to the splitter, and then tested with another ublox (a NEO > > 7M) via a BIAS-TEE that it could also see satellites and that both > > could get a 3D fix. > > > > When I connected up each of the M600's, they eventually acquired > > positions and acheived sync, but while the ublox receivers rarely do > > not show a 3d fix, both of the M600's will show the a similar number > > of satellites in view as the ublox, and sometimes more than one "Good" > > satellite, but the "Selected Satellite Set:" never seems to change > > from "00 00 00 00". > > When the receiver is powered up and has a good last known position and > almanac, it expects to be able to track the satellites that should be in > view at the given location. If those satellites can't be tracked then > they are kicked out, and the number of good satellites goes down to 0. > > Eventually with a few minutes delay, the receiver should enter "Warm > Boot" mode when this happens. In warm boot mode it tries to track any of > the 32 possible GPS satellites, and whenever a satellite has been found, > the number of "good" satellites is increased.
So if I understand you correctly, the number of "Good" satellits, is the number of tracked satellites ? > > If at least 4 satellites can be received, the receiver position is > determined / verified, and the receiver changes to "Normal Operation" again. > > See also the description here: > https://kb.meinbergglobal.com/kb/meinberg_gps_receivers > > > I presume that as its a timing device, that once it has surveyed its > > position, it only needs one satellite to solve for time, and the MRS > > status shows "Signal available, Is master, Is locked, Is accurate" > > with an offset that is usually within -50 to -120ns but I'm lost as to > > what the "Selected Satellite Set:" should be displaying. > > If more tha 4 satellites can be tracked, it should display the 4 main > satellites that yield the highest accuracy, depending on the constellation. So if I understand you correctly, the "Selected" part is only filled in if there are more than four tracked satellites ? > > > At the moment, one of the Meinbergs shows 10 in view and one good, and > > one of the ublox shows 12 in view and 8 used. > > This sounds like the input signal is not quite correct, or the device is > in "Warm Boot" mode where it has just detected a single satellite, but > is still searching. > > A single satellite is enough to keep the time if the stored position is > known to be the correct one, so the GPS signal propagation can be > accurately compensated. > > If the real position has changed, e.g. because the device has been > shipped from the previous owner to you, the compensation of the signal > propagation delay would be wrong if it is based on the previously saved > receiver position. > > This is why the GPS receiver only claims to be fully synchronized if it > has at temporarily tracked at least 4 satellites, and has verified or > determined its current geographic position. Both devices showed their previous location when initially powered on, I initialised both with cold boot, and both eventually acquired position, so I would presume that they both managed to acquire 4 satellites during this process. > > > I tried with one of the Meinberg's (via the GPS-CON) connected > > directly to the antenna with no improvement, and tried with a patch > > antenna directly connected, again with no improvement, and different > > ports on the splitter etc. > > That won't work if the assumption is correct that the built-in GPS > receivers are models that expect a down-converted signal. Apologies, that was badly written by me, I tested both a patch antenna and the dual band antenna direct to a GPS-CON to a M600, and via the splitter to the GPS-CON to the M600, and each setup with each GPS-CON and each M600, there was no obvious difference between any of them > > > The antenna location is by no means ideal (west facing window in > > fairly central London), but none of the ublox receivers (just basic > > Max8 and Neo7m, no timing ones yet) have had any trouble getting and > > keeping a 3D fix.> > > From my "naive" viewpoint, it looks as if the Meinbergs are a little > > "deaf", but I'm guessing that I'm missing something. > > I have to confirm that some current 3rd party receiver models are more > sensitive than the Meinberg ones, so they may be able to track signal > that are just reflected by walls of the surrounding signals. > This is what I clumsily meant by "deaf" > Anyway, the best approach for a reliable, continuous operation is to > install the antenna in a location with sufficient view to the sky. > The fun of being in a ground floor flat, getting the dual band antenna mounted to the chimney stack is planned > > Any suggestions gratefully received. > > You could also contact techsupp...@meinberg.de for support. Those guys > will even help you, if possible, even if you have acquired your devices > from someone else, and even if the devices are old. > > It would be good to provide for each device at least the serial number, > or even better the diagnostics file that can be generated via the web > interface, so the guys know enough details to be able help you. > I'll wait untill I either can take them somewhere with a good skyview, or I can get the dual band antenna mounted, as I think it might just be the poor antenna position combined with the sensitivity. > Depending on the device details, there even may be firmware updates > available that you can install on your devices. Both devices were initially running firmware that was at least two releases old, both have already been updated to current (-: > > Martin (working at Meinberg) > Many thanks for your very informative reply! Cheers Arne _______________________________________________ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe, go to http://lists.febo.com/mailman/listinfo/time-nuts_lists.febo.com and follow the instructions there.