[time-nuts] Does a frequency counter locked to GPS need to "warm up"?

[Chris Wilson]

  08/02/2018 07:31

Does  a  frequency  counter  connected  to a permanently running (Trimble 
Thunderbolt) GPS
disciplined frequency standard need to warm up after switch on before readings 
settle?
Just curious, thanks.

-- 
   Best Regards,
   Chris Wilson.
mailto: ch...@chriswilson.tv

___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Receiving the MSF time signal on cheap radio modules

[Poul-Henning Kamp]

In message 
, "Deirdre 
O'Byrne" writes:

>I've updated my paper, which now contains the attached graph. (I did a
>linear regression analysis to see what the correction for the receivers
>should be, and I applied receiver 2's correction to both receivers to
>generate this graph).

Yes, these cheap "clock-receivers" vary a lot and they are usually also
very temperature sensitive.

-- 
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@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

[time-nuts] PulsePuppy Status

[John Ackermann N8UR]

For those who ordered a PulsePuppy oscillator carrier board from TAPR -- 
we quoted early February delivery so I wanted to give a quick update.


The boards are in hand and the kits ready to go, except... USPS managed 
to lose the box of programmed PICs on its way from my house to the TAPR 
office.  I should be getting a new batch from Mouser tomorrow, and have 
them on the way back to the office by Monday (via UPS this time).  With 
luck, we should be able to ship kits by the end of next week.


Sorry for the delay; if not for the lost package we would have shipped 
last week.


(If you're not familiar with the PulsePuppy, here's the link: 
https://www.tapr.org/kits_pp.html.  We'll have plenty of kits available 
once the PIC chip problem is solved.)


John
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Receiving the MSF time signal on cheap radio modules

[Deirdre O'Byrne]

No doubt! But I'm trying to remain as inexpensive as possible.

That it might be possie to get 5ms (300 carrier periods!) from an
off-the-shelf consumer-grade component not designed for accuracy is pretty
cool IMO.


On 7 Feb 2018 14:31, "Bob kb8tq"  wrote:

Hi

Back in the era of VLF disciplined oscillators, carrier phase was the
preferred approach.
Getting that to work with 100% AM modulation took some effort ….

Bob

> On Feb 7, 2018, at 2:13 AM, Poul-Henning Kamp  wrote:
>
> 
> In message , "Deirdre O'Byrne" writes:
>
>> MSF disciplined oscillator?! I don't trust these receivers to any better
>> than about the 20ms mark, so such a disciplined oscillator would have
quite
>> a long integration time!
>
> It's actually more complicated and better than that.
>
> The low-pass filter dominates, so the falling flank at second N
> depends on the pulsewidth at second N-1.
>
> I can't remember the numbers I got when I "sorted" DCF77 pulses depending
> on the previous pulse being short or long, but it was a fair bit better
> than 20ms.
>
> --
> 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@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/
mailman/listinfo/time-nuts
> and follow the instructions there.
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] eBay GPS antenna discussion.

[John Green]

Dr. David Kirkby wrote:
Another RF engineer, who I don't know from working with antennas, said to
me that antennas are a still a charlatan's paradise.

Those words rang true to me. I have yet to see a yagi type antenna that, in
practice actually produced the gain it was specified to produce. True, I
don't have a proper chamber in which to test antennas. I can only do real
world comparisons. I have a pretty large collection of various 900 mHz
antennas and on occasion, I set up my home made antenna test range and do
measurements. This consists of a 900 MHz handie talkie with power turned
down as low as it will go and PTT fastened down with a rubber band. Several
hundred feet away, on a deck attached to my house at a height of about 10
feet, I have an HP 8924C to measure levels. First, I measure a home made
groundplane for reference. Then the antennas to be tested are attached and
measured. I realize that there are multiple places where error can and does
creep in. But, I have found that when I actually try to use the antennas
tested, the results are pretty accurate for real world conditions. I
haven't found a good way just yet to test GPS antennas. There are just too
many things besides gain to be considered. Many of which are beyond my
capabilities.
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Anyone have experience with this antenna?

[Bob kb8tq]

Hi

They probably have a group of people on staff to go out and dry them off after 
it rains …. :)

Indeed, there are a lot of pictures of heated enclosures for antennas. The 
debate over the
dielectric properties of the coverings goes back a long way. There are notes in 
the standard
databases for the antennas that came with optional covers. They have a separate 
data file
for the “with cover” and “without cover” versions. The discussion here is 
pretty much an 
replay of how the conversation has gone over the years. There is indeed a group 
of people
who (quite rightly) suggest that it’s not a big deal in most cases. 

Bob

> On Feb 7, 2018, at 10:07 AM, Poul-Henning Kamp  wrote:
> 
> 
> In message <875e4bc6-32c3-4724-afcd-086553ae5...@n1k.org>, Bob kb8tq writes:
> 
>> Water wise, one might note the large piles of snow sitting on my antennas at 
>> the moment. Yes, I 
>> could go knock it off, but somehow it just keeps coming back. Weird how 
>> winter works …. There
>> is no perfect solution. 
> 
> Somebody at BIPM told me that their antennas were heated and thermostatically
> kept at constant temperature.
> 
> -- 
> 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@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Anyone have experience with this antenna?

[Poul-Henning Kamp]

In message <875e4bc6-32c3-4724-afcd-086553ae5...@n1k.org>, Bob kb8tq writes:

>Water wise, one might note the large piles of snow sitting on my antennas at 
>the moment. Yes, I 
>could go knock it off, but somehow it just keeps coming back. Weird how winter 
>works …. There
>is no perfect solution. 

Somebody at BIPM told me that their antennas were heated and thermostatically
kept at constant temperature.

-- 
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@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Anyone have experience with this antenna?

[Bob kb8tq]

Hi

It’s not the end stops that are the issue. It’s the wall of the pipe. If the 
dimensions in 
the sketch are roughly correct and you scale it to the dimensions of the eBay 
antenna,
that is a big tall pipe. Indeed “nothing overhead” would mitigate part of the 
issue. That magic
line runs roughly along Hadrian’s Wall in the UK. I’d bet that 80 degrees 
overhead would still be
an issue. 

Again, this is an extreme case and not the typical cover for a GPS antenna. 

Water wise, one might note the large piles of snow sitting on my antennas at 
the moment. Yes, I 
could go knock it off, but somehow it just keeps coming back. Weird how winter 
works …. There
is no perfect solution. 

Bob

> On Feb 7, 2018, at 3:59 AM, Poul-Henning Kamp  wrote:
> 
> 
> In message 
> 

Re: [time-nuts] Receiving the MSF time signal on cheap radio modules

[Bob kb8tq]

Hi

Back in the era of VLF disciplined oscillators, carrier phase was the preferred 
approach. 
Getting that to work with 100% AM modulation took some effort ….

Bob

> On Feb 7, 2018, at 2:13 AM, Poul-Henning Kamp  wrote:
> 
> 
> In message 
> , 
> "Deirdre O'Byrne" writes:
> 
>> MSF disciplined oscillator?! I don't trust these receivers to any better
>> than about the 20ms mark, so such a disciplined oscillator would have quite
>> a long integration time!
> 
> It's actually more complicated and better than that.
> 
> The low-pass filter dominates, so the falling flank at second N
> depends on the pulsewidth at second N-1.
> 
> I can't remember the numbers I got when I "sorted" DCF77 pulses depending
> on the previous pulse being short or long, but it was a fair bit better
> than 20ms.
> 
> -- 
> 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@febo.com
> To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.

___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] eBay GPS antenna.

[ewkehren via time-nuts]

Please keep us informed I bought onBert Kehren


Sent from my Galaxy Tab® A
 Original message From: John Green  Date: 
2/6/18  4:03 PM  (GMT-05:00) To: time-nuts@febo.com Subject: Re: [time-nuts] 
eBay GPS antenna. 
I kind of have to believe the specs. The two survey grade antennas I
already have, a Leica and a Trimble, both have regulators in the preamp
sections. The Leica has an 8 volt one and the Trimble has a 5 volt one. I
intend to hook it up to a variable supply and watch the current as I
increase voltage. If it has a regulator, the current should stabilize at an
input voltage just above what the internal preamp operates at. If not, it
should continue to rise. I am tempted to pry it apart, even if it risks
damage just so I can see for myself what they are using for the preamp
stages.
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Anyone have experience with this antenna?

[Dr. David Kirkby]

On 6 February 2018 at 03:33, John Green  wrote:

> https://www.ebay.com/itm/High-Precision-L1-L2-GNSS-GPS-GLONA
> SS-BeiDou-RTK-CORS-survey-antenna/162718512935?ssPageNam
> e=STRK%3AMEBIDX%3AIT&_trksid=p2060353.m2749.l2649
>
> Listed on eBay as a L1/L2 antenna with decent specs.


I used to work in the antenna industry selling 'professional' antennas -
not aimed at the amateur radio market. Many specifications are invented to
be better than a competitor. The competitors do it too, so it is not just
one company. If you sell antennas with valid specifications, it would be
next to impossible to sell them, as competitors will have higher
specifications.

Another RF engineer, who I don't know from working with antennas, said to
me that antennas are a still a charlatan's paradise.

With antennas, probably more than any other device, I would believe the
specifications if I could verify them. Unfortunately, for that sort of
antenna, I don't know how to verify them.

If nothing else, I would ask the seller for a copy of the test reports that
back up the specifications.

I got a couple of WiFi antennas free from eBay, after proving the gain
specifications were vastly exaggerated. Depending on the phase of the moon,
the numbers that came up in last months lottery, eBay policy changes with
reguard to who pays the return shipping fee on items that are not as
described. If you can show its the seller, then in many cases they will not
wish to pay the return cost.

Dr David Kirkby Ph.D C.Eng MIET
Kirkby Microwave Ltd
Registered office: Stokes Hall Lodge, Burnham Rd, Chelmsford, Essex, CM3
6DT, United Kingdom
Registered in England and Wales as company number 08914892
http://www.kirkbymicrowave.co.uk/
Tel 01621'680100 / +44 1621-680100 <01621%20680100>
___
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.

Re: [time-nuts] Anyone have experience with this antenna?

[Poul-Henning Kamp]

In message 

Re: [time-nuts] Anyone have experience with this antenna?

[Michael Wouters]

That does represent a limiting case but it's a bit pessimistic. The longest
path is for very shallow incident angles eg a 3 mm thick and 150 mm radius
disk gives an angle of only about 1 degree. At 10 degrees, the path is
about 20 mm; with a refractive index of 1.5, the path is only 10 mm longer.
10 degrees might be what you set in the receiver's elevation mask.

A mm thick layer of dirt is just going to be roughly another mm of plastic;
worse if it's absorbed moisture, true.

You have a point about water. Water has about 10 times the refractive index
of plastic (real part of n)  so this is more of a worry. A 1 mm film will
have triple the path through a nominal 3 mm of plastic so at 10 degrees
incidence there is now about 40 mm extra path which you might see in
post-processing. But you're not going to see that in the 1 pps.

Cheers
Michael

On Wed, 7 Feb 2018 at 8:14 am, Bob kb8tq  wrote:

> Hi
>
> Since we are talking about an L1 / L2 antenna here, a reasonable assumption
> would be that the target is something better than an “average result”. If
> you construct
> a cover out of a piece of PVC pipe (as shown in the original drawing),
> your worst
> case path has a foot or so of PVC in it compared to a best case path with
> well under
> a tenth of an inch. That’s going to give you a bit of variation ….. Add
> some dirt or water
> or ice to the equation and who knows what the result might be.
>
> Bob
>
> > On Feb 6, 2018, at 3:45 PM, Michael Wouters 
> wrote:
> >
> > I can see why the geodetic community would worry about antenna phase
> centre
> > variation when a radome is installed but is it really an issue in timing
> > applications? The few papers I've read suggest PCVs of less than 10 mm,
> or
> > equivalently, 30 ps. This is at the level of precision available from
> > post-processed, carrier phase time-transfer but  invisible in the 1 pps
> > coming out of your receiver, even with a good sawtooth correction. Am I
> > missing something?
> >
> > Cheers
> > Michael
> >
> > On Wed, 7 Feb 2018 at 4:14 am, Bob kb8tq  wrote:
> >
> >> Hi
> >>
> >> There are “cell site” specific GPS antennas on the market. Panasonic has
> >> had one out
> >> for quite a while. I’m sure there are several others.
> >>
> >> One issue with doing any sort of “cover” for a precision antenna is
> >> distorting it’s pattern.
> >> Plastic (or whatever you use) will have different properties than air. A
> >> path through a blob
> >> of “not air” will change the effective path length. That impacts the
> >> timing and thus the
> >> navigation solution. If you are worried about 2mm sort of pattern
> >> accuracy, things get
> >> tricky. Early on, there was a big “throw out the radomes push when this
> >> was first noticed.
> >>
> >> Bob
> >>
> >>> On Feb 6, 2018, at 6:15 AM, Bo Hansen  wrote:
> >>>
> >>> Hi
> >>>
> >>> Besides the RF characteristics it may also be worth considering the
> >> quality of the plastics used. Over time water ingress may become an
> issue.
> >> Fours years after the installation of a CN brand antenna, sourced
> locally
> >> so probably not counterfeit either, we had to replace it at OZ7IGY
> >> www.oz7igy.dk
> >>>
> >>> RF wise 42 dB of gain IS an issue. Again at OZ7IGY, with 12 carriers in
> >> the air especially 13 cm and 23 cm, blocking and IMD were an issue
> before
> >> we mounted a BPF. I have taken apart the above mentioned antenna, a
> >> Motorola antenna and an eBay "hockey puck" antenna. The best design was
> >> clearly the Motorola one because it had a BPF after the pre-amp -
> probably
> >> because it was designed by RF competent people too. Each of the other
> ones
> >> had two FETs/MMICs in series and then a BPF. Of cause if no nearby
> carriers
> >> are in the air it may be less of an issue.
> >>>
> >>> So designing a really good antenna and pre-amp may be a business
> >> opportunity. There are many hi IP3 MMICs available designed for GPS and
> the
> >> like purposes. SAW BPFs with <1 dB loss are available fairly cheap so
> one
> >> before the FET/MMIC with a 1 dB NF is the way to go. A DIY radome using
> >> standard materials from any hardware shop is attached.
> >>>
> >>> Bo, OZ2M
> >>>
> >>> ___
> >>> time-nuts mailing list -- time-nuts@febo.com
> >>> To unsubscribe, go to
> >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> >>> and follow the instructions there.
> >>
> >> ___
> >> time-nuts mailing list -- time-nuts@febo.com
> >> To unsubscribe, go to
> >> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> >> and follow the instructions there.
> >>
> > ___
> > time-nuts mailing list -- time-nuts@febo.com
> > To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> > and follow the instructions there.
>
>