Re: [time-nuts] Advantages of GNSS ???
Hey Graham, I'm gonna start a project soon to evaluate a F9P as a Time Transfer GNSS receiver. For now i haven't too much answers for you but only i know is: the BIPM uses all labs that participate from UTC to make corrections of GNSS satellites frequency, also for the TAI use. I think GNNS T is a good and reliable source for many projects. Here in my lab with Septentrio's Pola RX 3 Tr we have a very low Time Dilution Of Precision when the Glonass and all anothers becomes enabled, so our frequency if compared to all GNSS constallations is good, i think the same logic can be applied for frequency generation / distribution. What i want to say is: with more satellites of different constellations you can have a better end signal (more stable and reliable). Tests should be done. I hope can help more in the future. Best regards, Luiz Em sex, 5 de jul de 2019 às 23:00, Graham / KE9H escreveu: > I have several questions for the group, since there are several members > that have been able to start evaluating the uBlox F9P and perhaps the F9T > GNSS receivers. > > For the purposes of time and frequency determination, is there an advantage > to using the GNSS receivers, relative to just the US GPS? > > It appears that a really good GPS (only) based GPSDO can get into the 1e-11 > and perhaps the 1e-12 accuracy range. > > Does using the signals from GPS (USA), plus GLONASS (Russia), plus Beidou > (China), and plus Galileo (Europe), actually provide any improvement in > time/frequency accuracy? > > Is that what the F9P actually does, or only some sub-combinations of the > above? > > Down at that level of accuracy, do the four systems agree within 1 e-12, > anyway? > > Is there any advantage to using the GNSS for time/frequency? > > Does using the RTCM Corrections, needed to achieve the ~ 1 cm positioning > accuracy also improve time/frequency accuracy? > > The underlying question I am trying to get at is: Will a GNSS based GPSDO > have any advantage over a GPS-only, or a dual band L1/L2 GPS-only GPSDO? > > Thanks, > --- Graham > > == > ___ > 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. > ___ 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.
[time-nuts] E1938A source code/ firmware
Has anyone got this , is the PIC read data prohibited ? Is it still a closely guarded secret?, there were some very clever and novel ideas used in that slab, in my opinion. Glen ___ 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.
[time-nuts] Advantages of GNSS ???
I have several questions for the group, since there are several members that have been able to start evaluating the uBlox F9P and perhaps the F9T GNSS receivers. For the purposes of time and frequency determination, is there an advantage to using the GNSS receivers, relative to just the US GPS? It appears that a really good GPS (only) based GPSDO can get into the 1e-11 and perhaps the 1e-12 accuracy range. Does using the signals from GPS (USA), plus GLONASS (Russia), plus Beidou (China), and plus Galileo (Europe), actually provide any improvement in time/frequency accuracy? Is that what the F9P actually does, or only some sub-combinations of the above? Down at that level of accuracy, do the four systems agree within 1 e-12, anyway? Is there any advantage to using the GNSS for time/frequency? Does using the RTCM Corrections, needed to achieve the ~ 1 cm positioning accuracy also improve time/frequency accuracy? The underlying question I am trying to get at is: Will a GNSS based GPSDO have any advantage over a GPS-only, or a dual band L1/L2 GPS-only GPSDO? Thanks, --- Graham == ___ 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.
Re: [time-nuts] Aerial coax downlead placement
Am 05.07.19 um 23:26 schrieb Poul-Henning Kamp: In message <28f942e8-b61d-4fa5-929d-923184828...@n1k.org>, Bob kb8tq writes: Energy flow is indeed inside the cable if things are set up and operating correctly. Please note in this context that *nothing* about lightning strikes works the way you would assume it does. A friend of mine got his ham radio station pulverized by a lightning hit in the garden. He had written his PHD thesis on the breakdown mechanism when charge powers its way through gases. I call that an a posteriori field research addendum. ;-) Cables run inside steel tubes protect the steel tube from lightning current because copper is a better conductor than steel - in particular when the leading flank is measured in kV/uS and the current in kA. Likewise, a 90 degree bend or a loop on the cable is a huge inductance to get all that high frequency energy through, so lightning tend to jump from bends and loops, to less inductive paths if possible Be careful with EMI/EMC clam-on ferrites, they can explode in lightning strikes. Then I look upon my pole as a 2 meter long clamp-on ferrite. That 7 mm Aircell cable won't conduct much better than the pole, and the outside of the pole will look quite, eh, attractive, given that king size common mode choke. And then, at the 90° cable corner to my lab, the lightning bolt may continue downwards through earth on its highway to hell.. cheers, Gerhard (Unix V6 on 1 of the 5 PDP 11/40E that ever existed) ___ 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.
Re: [time-nuts] Aerial coax downlead placement
On 7/5/19 2:26 PM, Poul-Henning Kamp wrote: In message <28f942e8-b61d-4fa5-929d-923184828...@n1k.org>, Bob kb8tq writes: Energy flow is indeed inside the cable if things are set up and operating correctly. Please note in this context that *nothing* about lightning strikes works the way you would assume it does. Cables run inside steel tubes protect the steel tube from lightning current because copper is a better conductor than steel - in particular when the leading flank is measured in kV/uS and the current in kA. Likewise, a 90 degree bend or a loop on the cable is a huge inductance to get all that high frequency energy through, so lightning tend to jump from bends and loops, to less inductive paths if possible Actually, the inductance of a bend isn't much more than the inductance of a straight piece of wire of the same length. You have to have a complete loop before the inductance starts to rise, and even then, a 1 turn loop doesn't have huge inductance, it's multiple loops where the inductance starts to rise as Nturns^2. Straight wire has an inductance of about 1 microhenry/meter (very weakly dependent on diameter) But a more exact calculation says that a 31.4 cm piece of wire, 10mm in diameter has a self L of 0.26 microhenry. A loop that is 100mm in diameter with a 10mm diameter conductor has an inductance of about 0.15 microHenry. 100mm diameter is a length of 0.314 meters, so it actually has *less* inductance that a wire that's the length of the perimeter. A 1 meter diameter loop (perimeter 3.14 meters) has an inductance of 3 uH. Which is close to the self inductance of a 3.14 meter straight wire (4 uH) The origin of the "no sharp bends in lightning conductors" is more related to the flashover voltage to surroundings - A sharp 90 bend has a lower breakdown voltage than a gradual bend because the radius of curvature is smaller. There's also a mechanical stress effect - if you have a corner, the wire on one side of the corner is carrying a current at right angles the field from the other arm of the corner, and it will tend to move (violently, given the large peak currents) Be careful with EMI/EMC clam-on ferrites, they can explode in lightning strikes. ___ 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.
Re: [time-nuts] Aerial coax downlead placement
In message <28f942e8-b61d-4fa5-929d-923184828...@n1k.org>, Bob kb8tq writes: >Energy flow is indeed inside the cable if things are set up and operating >correctly. Please note in this context that *nothing* about lightning strikes works the way you would assume it does. Cables run inside steel tubes protect the steel tube from lightning current because copper is a better conductor than steel - in particular when the leading flank is measured in kV/uS and the current in kA. Likewise, a 90 degree bend or a loop on the cable is a huge inductance to get all that high frequency energy through, so lightning tend to jump from bends and loops, to less inductive paths if possible Be careful with EMI/EMC clam-on ferrites, they can explode in lightning strikes. -- Poul-Henning Kamp | UNIX since Zilog Zeus 3.20 p...@freebsd.org | TCP/IP since RFC 956 FreeBSD committer | BSD since 4.3-tahoe Never attribute to malice what can adequately be explained by incompetence. ___ 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.
Re: [time-nuts] It is possible to "recharge" a hydrogen maser?
Er du Norsk? Ole Petter Rønningen er et Norsk navn. -Original Message- From: Ole Petter Ronningen Sent: Friday, July 05, 2019 10:04 AM To: Discussion of precise time and frequency measurement Subject: Re: [time-nuts] It is possible to "recharge" a hydrogen maser? Just change the bottle, or hydride cartridge, whichever it is. But it is also very possible that the ion pumps are at the end of their lives, but these can also be replaced "easily". What type if maser is it? Ole On Fri, Jul 5, 2019 at 7:01 PM Luiz Paulo Damaceno < luizpauloeletric...@gmail.com> wrote: Hi friends, We have a hydrogen maser here at the university that i work. It seems the hydrogen is over. This is possible? If yes, It is possible to recharge It? Best regards, Luiz. ___ 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. ___ 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. ___ 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.
Re: [time-nuts] Aerial coax downlead placement
Hi The purpose of coax is to shield the signal. The outer portion of the cable acts to protect the inner part from stray signals in the environment. In a normal system, the outer braid is connected to ground. It is no different than a lot of audio cabling in that respect. Energy flow is indeed inside the cable if things are set up and operating correctly. If it was on the outside, the shield would not be doing its job of protecting things. This is only true to the extent that skin depth will allow it to happen. Why does this matter? With something like a 1 pps timing pule, some portion of the energy *will* be low enough in frequency to make it past the skin depth / thickness of any practical cable. The components that create the fast rising edge will be contained, but the low frequency stuff will not be. Fortunately we rarely use cables that are a significant fraction of a wavelength at 1 Hz :) Bob > On Jul 5, 2019, at 1:47 PM, Peter Vince wrote: > > On Fri, 5 Jul 2019 at 18:01, WigglePig wrote: > >> If there are currents in the braid to upset then your antenna system is >> not working as you might believe. >> > > I was working on the simplistic assumption that for a current to flow, > there must be a complete circuit, so the current flows down the centre > conductor, and must come back up the braid. But I gather that unlike DC, > RF is "black magic", and only flows on the inside of the braid - if all the > impedances match. > ___ > 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. ___ 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.
Re: [time-nuts] Aerial coax downlead placement
On Fri, 5 Jul 2019 at 18:01, WigglePig wrote: > If there are currents in the braid to upset then your antenna system is > not working as you might believe. > I was working on the simplistic assumption that for a current to flow, there must be a complete circuit, so the current flows down the centre conductor, and must come back up the braid. But I gather that unlike DC, RF is "black magic", and only flows on the inside of the braid - if all the impedances match. ___ 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.
Re: [time-nuts] It is possible to "recharge" a hydrogen maser?
Hi Luiz, We replaced H-source one Kvarz active HM during the summer of 2016. After 6-9 months of so of 'warm up' and settling down it is back up to maximum TAI weight. We got the new H-source bottle (size of a mini coke-can) and instructions from the manufacturer. >From what I recall the steps are roughly: - turn it off and turn it upside down - open up (HFO, mag-shield etc.) enough to have access to the H-bottle - disconnect the old bottle - cool down the new bottle in liquid nitrogen - connect new (cold) bottle with new seals (ethanol was used to prevent the new seals collecting water and freezing) - paint soap-bubble liquid on the pipes and look for leaks. let it warm up a day or two. - assemble, turn on, hope for the best :) - the bottle has a heater, which isn't needed in the beginning (6-9 months) when the H-pressure from the new source is high, so the heater can be off. Turn on the heater when the H-pressure monitor shows a reasonable value. hope this story helps, it's definitely doable with support from the manufacturer and basic tools/skills found in your typical time lab. Anders On Fri, Jul 5, 2019 at 8:01 PM Luiz Paulo Damaceno < luizpauloeletric...@gmail.com> wrote: > Hi friends, > > We have a hydrogen maser here at the university that i work. It seems the > hydrogen is over. This is possible? If yes, It is possible to recharge It? > > Best regards, > > Luiz. > ___ > 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. > ___ 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.
Re: [time-nuts] It is possible to "recharge" a hydrogen maser?
My experience is limited to the MHM-2010 at the Arecibo observatory, but I suspect they all handle the H2 supply in pretty much the same way. Th hydrogen comes from a reservoir, in the case of the MHM-2010 from a small "lecture" bottle of H2 under pressure. I assume that this is isotopically rather pure, and also fairly pure of other gaseous contaminants. In principle this should be field replaceable; however special procedures including a good vacuum pump and probably some special fittings would likely be required. You should consult the mfr of your maser about the availability of a new bottle of H2 as well as correct procedures for making the changeover. We at Arecibo had to replace one of the vacion pumps in our maser about 6 or 7 years ago. and we decided to get help from Symmetricom in the form of a field service call, to the tune of $12k. The guy who came was a physicist at heart, and was the very guy who had put together the physics package in our very maser. This included replacement of the still-working pump as well, done the following day. So on the first day, he replaced the failed pump while I asked questions and took copious notes. Then on the 2nd day, I replaced the 2nd pump while he kibitzed and stood ready to stop me before I did anything stupid. In both cases there was some difficulty getting the pumps "started up", arising because they had been open to the atmosphere for some time beforehand. They both required a lot of teasing of the voltage in little steps, while intently watching the current to be sure not to exceed ratings. IIRC, they each required more than an hour of vigilance before we could safely stand down. The interesting thing was that this maser could (and did) run quite well with only one pump working, for over a year. The delay was on our part, shuffling stuff around in the clock room to clear generous working space around the maser. The job involved a lot of "on-the-floor" work, much like working under a car without benefit of a lift. But the maser was well thought out in that subsystems could be isolated with high-vacuum valves and switches, with the result that we kept the maser operating throughout the two procedures, with only a subtle glitch in timing accuracy visible in the records when I checked after the fact. The observatory continued to operate with no disturbance the whole time. Dana Whitlow On Fri, Jul 5, 2019 at 12:01 PM Luiz Paulo Damaceno < luizpauloeletric...@gmail.com> wrote: > Hi friends, > > We have a hydrogen maser here at the university that i work. It seems the > hydrogen is over. This is possible? If yes, It is possible to recharge It? > > Best regards, > > Luiz. > ___ > 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. > ___ 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.
Re: [time-nuts] It is possible to "recharge" a hydrogen maser?
Hi Anything is possible. Working out exactly what happened and what needs to be done to fix it might be a bit involved. A maser is a pretty complicated piece of gear. The best bet is to dig out the manuals and go through the troubleshooting process in them. Plan for it taking a bit of time ….. Bob > On Jul 5, 2019, at 10:11 AM, Luiz Paulo Damaceno > wrote: > > H i friends, > > We have a hydrogen maser here at the university that i work. It seems the > hydrogen is over. This is possible? If yes, It is possible to recharge It? > > Best regards, > > Luiz. > ___ > 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. ___ 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.
Re: [time-nuts] It is possible to "recharge" a hydrogen maser?
Just change the bottle, or hydride cartridge, whichever it is. But it is also very possible that the ion pumps are at the end of their lives, but these can also be replaced "easily". What type if maser is it? Ole On Fri, Jul 5, 2019 at 7:01 PM Luiz Paulo Damaceno < luizpauloeletric...@gmail.com> wrote: > Hi friends, > > We have a hydrogen maser here at the university that i work. It seems the > hydrogen is over. This is possible? If yes, It is possible to recharge It? > > Best regards, > > Luiz. > ___ > 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. > ___ 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.
Re: [time-nuts] Aerial coax downlead placement
Hi, > Plus as the pole moves in the wind (they all do) the cable can move > about inside, and if repeatedly impacting the inside of the pole over > time, that will damage the cable. You fix the cable inside the pole by applying three cable ties as a triangle in regular intervalls. The loose ends of the cable ties will center the cable inside the pole. That is how we do it in sailing. You do not want a cable flapping against the inside of the mast, which is the pole. That does not solve the prolem of the cable weight, you need a pull relief anyway. Cheers Detlef DD4WV ___ 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.
Re: [time-nuts] Aerial coax downlead placement
If there are currents in the braid to upset then your antenna system is not working as you might believe. > On 5 Jul 2019, at 10:46, Peter Vince wrote: > > Thank you all for your replies. A case of a little knowledge being a bad > thing in my case. But at least I was aware of a potential problem to be > considered! :-) > > Thanks again, > > Peter > ___ > 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. ___ 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.
[time-nuts] It is possible to "recharge" a hydrogen maser?
Hi friends, We have a hydrogen maser here at the university that i work. It seems the hydrogen is over. This is possible? If yes, It is possible to recharge It? Best regards, Luiz. ___ 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.
Re: [time-nuts] Aerial coax downlead placement
On 05/07/2019 06:01, Gerhard Hoffmann wrote: >> Hello all, >> >> A new contact, whose background is in computer programming rather than >> RF, is getting into accurate GPS positioning, and has been tapping me for >> any knowledge I might have. I persuaded him to get the new Ublox F9P >> receiver and also a "proper" dual-band antenna - albeit from China, so >> affordable! This seems to be going quite well, and he sent a photo today. >> He has mounted said aerial on what looks like a six-foot pole which is >> good, but currently the coax down-lead is just hanging - flopping about in >> the breeze. Now that is bad for so many reasons :-) > I cannot think of a single good reason against putting the coax line > > into the pole. In fact, my rocket-shaped Datum antenna leaves me no > > other choice. Its plastic case has a ~ 1 1/4" thread that happily fits on a > > water pipe and the N connector is concentric to that; so the cable MUST > > go through the pole, at least initially. I think that is good also in > case of > > a thunderbolt hit; the tube will carry most of the current and lead it > to earth. > > That won't help the antenna, but maybe me in the lab. > > And it is the only true symmetrical solution. > > That rocket-shaped antenna spawns a lot of interest amongst my neighbors. > > :-) Gerhard > Well, it shouldn't "mess up" the cable characteristics, unless the cable is bad anyway, but... All the weight of the free hanging cable inside the pole will be supported by the connector on the antenna. Plus as the pole moves in the wind (they all do) the cable can move about inside, and if repeatedly impacting the inside of the pole over time, that will damage the cable. Best run it down the outside, clipped or tied at regular intervals to the pole, but not so tight as to distort the cable. In fact, if it's a long pole, you can wrap the cable around the pole as a very wide spaced spiral, that will help prevent vortex shedding as air passes over the pole, reducing wind powered oscillations. The pole will still bend a bit but should not sway about anyway near as much. Have Fun. Regards. Dave B G0WBX. -- Created on and sent from a Unix like PC running and using free and open source software: ___ 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.
Re: [time-nuts] Aerial coax downlead placement
Thank you all for your replies. A case of a little knowledge being a bad thing in my case. But at least I was aware of a potential problem to be considered! :-) Thanks again, Peter ___ 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.
Re: [time-nuts] Aerial coax downlead placement
In a (almost) ideal coaxial cable (almost) *all* RF electromagnetic field is inside the cable. Unlike ladder balanced transmission line where it is everywhere else in the universe. Leo > From: Peter Vince > sure of the best advice to give him. I'm sure I heard that you should > never drop the coax down the middle of your support-pole, as the conducting > pole will mess up the characteristics of the cable by affecting the > currents in the outer braid. ___ 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.
