[time-nuts] UBLOX 1pps vs Z3801A

Murray Greenman Murray.Greenman at rakon.com
Tue Dec 21 22:56:37 UTC 2010


John,
The Z3801A 1pps is based on the mean UTC/GPS time, but regenerated from
the local (very stable) 10MHz reference, so has little jitter.

The UBLOX GPS module 1pps output is more or less instantaneous, so has
jitter resulting from each individual position solution. If you provide
it with a known position, the jitter will be reduced, but still not as
good as the regenerated 1pps from the Z3801A. The jitter is much greater
if 'Selective Availability' is on.

One of the important factors in designing and building your own GPSDO is
to shield your stable OCXO from this timing jitter. The aim is to have
the going rate of the OCXO follow UTC/GPS, not the jitter, SA, fix
solution or diurnal satellite variations.

Murray ZL1BPU


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Today's Topics:

   1. West coast LORAN (Hal Murray)
   2. Re: UBLOX GPS board testing (John Green)
   3. Re: LORAN C antenna thoughts from the group (paul swed)
   4. Re: LORAN C antenna thoughts from the group (Poul-Henning Kamp)
   5. Re: West coast LORAN (paul swed)
   6. Re: UBLOX GPS board testing (paul swed)
   7. Re: LORAN C antenna thoughts from the group (paul swed)
   8. Re: What is the best way to multiply a 10 Mhz (Gerhard Hoffmann)


----------------------------------------------------------------------

Message: 1
Date: Tue, 21 Dec 2010 13:00:55 -0800
From: Hal Murray <hmurray at megapathdsl.net>
Subject: [time-nuts] West coast LORAN
To: time-nuts at febo.com
Message-ID:
	<20101221210055.66C1880003B at ip-64-139-1-69.sjc.megapath.net>
Content-Type: text/plain; charset=us-ascii


Has anybody on the west coast tried to pick up LORAN stations from north
west 
Pacific?

Does anybody have any idea of how long those transmitters are likely to
keep 
running?


-- 
These are my opinions, not necessarily my employer's.  I hate spam.






------------------------------

Message: 2
Date: Tue, 21 Dec 2010 15:26:54 -0600
From: John Green <wpxs472 at gmail.com>
Subject: Re: [time-nuts] UBLOX GPS board testing
To: time-nuts at febo.com
Message-ID:
	<AANLkTi=9ae5k216qMOPZq+VE0w9V5w8-2evgvdi2GLNr at mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1

I tried substituting the 1 PPS output from the Z3801 and comparing it
to its own 10 MHz output and find the same jumpy behavior as I get
with the UBLOX boards. Well, not exactly the same but pretty much. Now
I am confused. I expected the 1 PPS to be in lock step with the 10
MHz.



------------------------------

Message: 3
Date: Tue, 21 Dec 2010 17:09:10 -0500
From: paul swed <paulswedb at gmail.com>
Subject: Re: [time-nuts] LORAN C antenna thoughts from the group
To: jfor at quik.com, Discussion of precise time and frequency
	measurement	<time-nuts at febo.com>
Message-ID:
	<AANLkTimSQsHE+YEhhhydw2V2Edj855SszT78mpQChz0o at mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1

John I believe that it is usable certainly from the pre-amplified whip
that
I picked up 90070 last night on.
The downside is you have to be awake at 0300. One of those nights.
As I mentioned my GPS comparison was not very good because I forgot to
rehook the gps antenna up to the hp3801. Doaaaa. Explains that pretty
well.

Is there a real advantage to a 4 or 6 foot big loop compared to a small
loop?
I use a 3 foot loop on wwvb/preamp and that works well.

One other point on the wavefrom on loran c. It was constructed to
minimize
the impact of skywave influence on the receiver. Essentially making it
easier for the receiver to distinguish between the two. Thast what I
hadread
in the loran docs.
Regards
Paul.
PS I thought the bw was +/- 10KC and even wider.

On Tue, Dec 21, 2010 at 3:11 PM, J. Forster <jfor at quik.com> wrote:

> I was more interested in reducing the BW, rather than increasing it.
>
> Years ago, I bought up some of the resuidual of Appelco, a New
Hampshire
> LORAN company that made units for Raytheon. Included were a bunch of
> active tunable filters, designed to "tune out" interference. However,
> there is no documentation.
>
> I was just toying with the idea that a good shielded (possibly active)
> loop, the tunable filters, and an Austron 2100F might still be usable
on
> the east coast.
>
> FWIW,
>
> -John
>
> ================
>
> > In message
<53187.12.6.201.2.1292957970.squirrel at popaccts.quikus.com>,
> "J.
> > Fors
> > ter" writes:
> >
> >>I remember reading somewhere that the envelope of the LORAN pulses
was
> >>shaped to reduce the transmitted BW.
> >
> > The envelope is designed for two things:  sensible BW and ease of
> > production.  There is some math musing about it in the Radiation Lab
> > book.
> >
> >>Does anybody have a reference for that, and relatedly, what does the
BW
> >> of
> >>the antenna have to be? Typically, loops are about 90 KHz to 110
KHz, but
> >>can that be narrowed down?
> >
> > In principle you can make it as narrow as you want, and compensate
> > for the resulting pulse-shape distortion in your receiver.
> >
> > Going much wider than 30kHz (85-115kHz) usually results in more
> > interference from CW signals than improvement to the loran signal.
> >
> > You can see a typical power spectrum at the bottom of this page:
> >
> >       http://phk.freebsd.dk/loran-c/Antenna/
> >
> > Poul-Henning
> >
> > --
> > Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> > phk at 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 at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>


------------------------------

Message: 4
Date: Tue, 21 Dec 2010 22:14:39 +0000
From: "Poul-Henning Kamp" <phk at phk.freebsd.dk>
Subject: Re: [time-nuts] LORAN C antenna thoughts from the group
To: paul swed <paulswedb at gmail.com>
Cc: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Message-ID: <9004.1292969679 at critter.freebsd.dk>

In message
<AANLkTimSQsHE+YEhhhydw2V2Edj855SszT78mpQChz0o at mail.gmail.com>, paul
 swed writes:

>Is there a real advantage to a 4 or 6 foot big loop compared to a small
>loop?
>I use a 3 foot loop on wwvb/preamp and that works well.

There is a very good and simple explanation of the theory behind
loops here:

	http://www.vlf.it/octoloop/rlt-n4ywk.htm

Sensitivity rises with the area of your loop, so doubling the diameter
gives you four times the signal, which may or may not be a relevant
low number of dB.

>One other point on the wavefrom on loran c. It was constructed to
minimize
>the impact of skywave influence on the receiver. Essentially making it
>easier for the receiver to distinguish between the two. Thast what I
hadread
>in the loran docs.

Yes, this is why you should always zoom in on the 3rd positive
zero-crossing.  Inside the announced service areas, the skywave will
never arrive early enough to disturb the groundwave at that point.

>PS I thought the bw was +/- 10KC and even wider.

Yes, it is, but the amount of actual energy once you get past 
+/- 10kHz or 15kHz is very very limited.

The perfect bandwidth is where the S/N of the loran-C signal
is 1:1, but I have never found a good way to determine that
automatically.

-- 
Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
phk at 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.



------------------------------

Message: 5
Date: Tue, 21 Dec 2010 17:16:46 -0500
From: paul swed <paulswedb at gmail.com>
Subject: Re: [time-nuts] West coast LORAN
To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Message-ID:
	<AANLkTimDWkbEFu1W_Vh7FY6Qgr46VaQWEqmUZgSeRodL at mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1

No idea at all. I am a east coaster.

On Tue, Dec 21, 2010 at 4:00 PM, Hal Murray <hmurray at megapathdsl.net>
wrote:

>
> Has anybody on the west coast tried to pick up LORAN stations from
north
> west
> Pacific?
>
> Does anybody have any idea of how long those transmitters are likely
to
> keep
> running?
>
>
> --
> These are my opinions, not necessarily my employer's.  I hate spam.
>
>
>
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>


------------------------------

Message: 6
Date: Tue, 21 Dec 2010 17:17:51 -0500
From: paul swed <paulswedb at gmail.com>
Subject: Re: [time-nuts] UBLOX GPS board testing
To: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Message-ID:
	<AANLkTi=7=UPyLkBqwuVHBHadx_UBdLBGABtD9dWyuo60 at mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1

Don't be burting my trust bubble here.
I would have thought they would be the same.
Now you are making me think.

On Tue, Dec 21, 2010 at 4:26 PM, John Green <wpxs472 at gmail.com> wrote:

> I tried substituting the 1 PPS output from the Z3801 and comparing it
> to its own 10 MHz output and find the same jumpy behavior as I get
> with the UBLOX boards. Well, not exactly the same but pretty much. Now
> I am confused. I expected the 1 PPS to be in lock step with the 10
> MHz.
>
> _______________________________________________
> time-nuts mailing list -- time-nuts at febo.com
> To unsubscribe, go to
> https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
> and follow the instructions there.
>


------------------------------

Message: 7
Date: Tue, 21 Dec 2010 17:20:14 -0500
From: paul swed <paulswedb at gmail.com>
Subject: Re: [time-nuts] LORAN C antenna thoughts from the group
To: Poul-Henning Kamp <phk at phk.freebsd.dk>
Cc: Discussion of precise time and frequency measurement
	<time-nuts at febo.com>
Message-ID:
	<AANLkTimEaD1fntVnRCe7Pc7YR3SbdBz2KUd01LoopdW=@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1

Thanks will read the link. Think I have in the past but did not have a
need.
I might guess 4 db would be quite helpful in this effort.
I still have some garbage I am seeing that I will need to hunt down. But
its
not within the house so that really makes things interesting.

On Tue, Dec 21, 2010 at 5:14 PM, Poul-Henning Kamp
<phk at phk.freebsd.dk>wrote:

> In message
<AANLkTimSQsHE+YEhhhydw2V2Edj855SszT78mpQChz0o at mail.gmail.com<AANLkTimSQ
sHE%2BYEhhhydw2V2Edj855SszT78mpQChz0o at mail.gmail.com>>,
> paul
>  swed writes:
>
> >Is there a real advantage to a 4 or 6 foot big loop compared to a
small
> >loop?
> >I use a 3 foot loop on wwvb/preamp and that works well.
>
> There is a very good and simple explanation of the theory behind
> loops here:
>
>        http://www.vlf.it/octoloop/rlt-n4ywk.htm
>
> Sensitivity rises with the area of your loop, so doubling the diameter
> gives you four times the signal, which may or may not be a relevant
> low number of dB.
>
> >One other point on the wavefrom on loran c. It was constructed to
minimize
> >the impact of skywave influence on the receiver. Essentially making
it
> >easier for the receiver to distinguish between the two. Thast what I
> hadread
> >in the loran docs.
>
> Yes, this is why you should always zoom in on the 3rd positive
> zero-crossing.  Inside the announced service areas, the skywave will
> never arrive early enough to disturb the groundwave at that point.
>
> >PS I thought the bw was +/- 10KC and even wider.
>
> Yes, it is, but the amount of actual energy once you get past
> +/- 10kHz or 15kHz is very very limited.
>
> The perfect bandwidth is where the S/N of the loran-C signal
> is 1:1, but I have never found a good way to determine that
> automatically.
>
> --
> Poul-Henning Kamp       | UNIX since Zilog Zeus 3.20
> phk at 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.
>


------------------------------

Message: 8
Date: Tue, 21 Dec 2010 23:46:53 +0100
From: Gerhard Hoffmann <dk4xp at arcor.de>
Subject: Re: [time-nuts] What is the best way to multiply a 10 Mhz
To: time-nuts at febo.com
Message-ID: <4D112E5D.2040002 at arcor.de>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed

Am 21.12.2010 21:41, schrieb Rick Karlquist:
> No, this is a fallacy because phase noise adds coherently, so that
each
> doubler adds 6 dB and each tripler adds 9.54 dB.  There is no way to
get
> around 20 LOG N, no matter how you implement the multiplier even if
> you add a tripler output to a quadrupler output, where phase noise
also
> adds coherently.
Yes, it adds coherently because it stems from the same source.

It is easier to see in the time domain: 1ps of jitter on a 10 MHz
carrier,
when multiplied to 100 MHz is still 1 ps of jitter, just look at the
zero crossings. But at 100 MHz, the jitter percentage of 1 ps to the
360?
is 10 times as bad, because the 360 degrees/s have shrunk.
So, a phase detector will give 10 times the output voltage or
20 dB more power. No way around this.

Gerhard, dk4xp



------------------------------

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