[time-nuts] Re: GPS failed
Hi, if you're worried about in-band interference, the 23cm HAM radio band is reasonably close to the L1 GPS frequency. When I was still active in packet radio back in the days, our digipeater DB0DAR lost an interlink due to interference with a precision GPS receiver in use by another university institute. We had to shut it down. I think they operated a DGPS site at the time and our link traffic caused errors in the correction data. Or something. BR, Matthias On Montag, 11. Juli 2022 01:19:18 CEST skipp Isaham via time-nuts wrote: > Hello to the Group, > > I'd like to get some opinions and war stories regarding GPS reliability at > high RF level and elevation locations. > > Background: Three different hill-top GPS receivers, all different types, > using different antennas mounted on an outside fixiture, plain view of the > open sky, all stopped working. > > Test antennas were brought in and placed on a fixture well away from the > original antennas, the recevers went back in to capture and lock. > > From what I understand, the original antennas are what I would call straight > preamp with no pre-selection / filtering. > > The ordered and now inbound replacements are said to contain a SAW filter > system. It is the intent of the client to just place these "improved > antennas" in to service and get on with life. > > I would suspect a GPS antenna (and receiver) could be subject to RF overload > or blocking, however, we're assuming nothing major has changed at the site, > nor any nearby location. One might think there are more GPS receivers > being pushed out of reliable operation by the world around them, I'm just > not hearing those stories from a lot of people using them (GPS receivers). > > Any new install GPS receiver antenna ordered will/should contain some > pre-selection to potentially avoid a problem, even some years down the > road? Seems like that's where things are going... no more off the shelf, > wide band, (hot) preamplified GPS antennas in busy locations? > > Thank you in advance for any related comments and/or opions ... > > cheers, > > skipp > > skipp025 at jah who dot calm > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: DIY Low offset Phase Noise Analyzer (Erik Kaashoek)
On Sonntag, 10. Juli 2022 01:24:49 CEST djl via time-nuts wrote: > I checked the Hittite/AD part at Mouser, $21 and change. Problem is, > they have a few, but it is marked obsolete/discontinued. Also, a > devilish package to work with. . . For a one-off project, lifetime doesn't really matter, does it? The package is QFN, even with center pad. That is inconvenient, but not too bad. It's just kind of small, 4mm edge length. You'd certainly need a microscope and hot air to solder it or a quite fine soldering tip if you would want to deadbug it. Were I to use it, and wanted to breadboard a prototype, I'd certainly make a suitable breakout board for easier handling. > On 2022-07-08 22:19, Mike Monett via time-nuts wrote: > > To Bob kb8tq. You wrote: > >> Hi > >> > >> The noise floor of the double balanced mixer (used as a phase > >> detector at 100 MHz) is in the -165 go -170 dbc / Hz range. I've > >> used the parts you are talking about. Their floor is *way* higher. > >> > >> Bob > > > > I stated the MC100EP140 would not match the Hittite HMC984LP4E. It has > > -231 dBc/Hz noise. > > > > -231 dBc is *way* lower than -170 dbc. About 60 dB lower. > > > > You might be interested in trying it. Only $13.25 at Arrow: > > > > https://octopart.com/search?q=HMC984LP4E > > > > Thanks, > > > > Mike > > ___ > > time-nuts mailing list -- time-nuts@lists.febo.com > > To unsubscribe send an email to time-nuts-le...@lists.febo.com > > > When in trouble, when in doubt, > Run in circles, scream and shout. > (Naval War College Football Team) > -- > Dr. Don Latham AJ7LL > PO Box 404, Frenchtown, MT, 59834 > VOX: 406-626-4304 > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: Knowing when the PPS signal is locked to the satellite.
On Mittwoch, 22. Juni 2022 14:59:29 CEST Dave via time-nuts wrote: > I am using a NEO-6M to provide a PPS signal for an experiment but I need > to know when it is locked or not. > > Does anyone know if there is a way to find out from either the NMEA data > stream or via the proprietary protocol ?? You can check e.g. the UBX-NAV-PVT message, if will tell you if the receiver has a valid UTC time and also the time uncertainty and what type of fix generated the nav solution. Or, UBX-NAV-TIMEUTC. Or, just UBX-NAV-STATUS. You can assume that as soon as a 3D or TIME fix is reported, the PPS is locked to GPS, or once the time uncertainty drops below a certain threshold. Note that this is what an M8 receiver will provide. I don't have any manual for the M6 receivers at hand, so the actual messages might be different for a M6 which supports a different protocol version than the M8. > At the moment I have it programmed to only provide a PPS signal when it > is locked (or nothing if not) and monitor > the PPS signal in the microprocessor, but it's not entirely satisfactory > and I need a better mechanism. That's not a bad mechanism actually. The PPS output is practically useless while the receiver is not locked to GPS. ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
[time-nuts] Re: Ublox M6T -M8T
Hi Rich, I'm using a LEA-M8T in a GPSDO project. I've gathered a bit of experience with the M8 timing receivers over the past two or three years. Both timepulse outputs can be programmed to any frequency and duty cycle you like, 10kHz is certainly not a problem. However, some things to consider: Only frequencies that are even multiples of the internal crystal frequency (48MHz) are "clean". Everything else is, as Bob puts it, "drop a pulse, add a pulse" approximations. However, that's normally easy to filter. The receiver adjusts the phase of the time signal once every measurement interval. That means, you'll typically get a phase jump every one second. You can adjust the measurement frequency, 5Hz is certainly possible, maybe more, but consult the data sheet on that. On top, there is the quantization error. The phase of the time signal will be off by some 20 nanoseconds against the "true" GNSS time. The error will be different for each measurement interval. If you want to use the time signal as a PLL reference frequency, your loop filter will have to be quite narrow to compensate for all these effects. BR, Matthias On Samstag, 28. Mai 2022 19:05:36 CEST R&M Putz via time-nuts wrote: > Has anyone done anything with the Ublox GPS timing receivers? As it appears > the Navman with the 10khz outputs seem to be drying up, I'm wondering about > the Time Pulse 2 output being set to 10 Khz or 100 Khz. Thoughts anyone? > Rich > W9ENG > ___ > time-nuts mailing list -- time-nuts@lists.febo.com > To unsubscribe send an email to time-nuts-le...@lists.febo.com ___ time-nuts mailing list -- time-nuts@lists.febo.com To unsubscribe send an email to time-nuts-le...@lists.febo.com
