Re: [time-nuts] Maser 0.7 nsec jumps solved

[Andy]

On Wed, May 25, 2016 at 12:59 PM, Mike Monett 
wrote:

LTspice shows  switching  at 0V is the best point in  time.  ...



Bzzzt!  Your simulation is seriously flawed, and your conclusions are
wrong.  What you forgot, or may not have realized, is that SPICE's initial
transient solution is obtained by having the signal sources already turned
on (at the moment of the Big Bang) and set to their initial value, so the
current through L2 is limited by DC conditions.  That is not anything close
to switching the driving voltages on.  It is having one waveform sit at
+169.7V DC for a very long time ('forever'), and then letting it follow a
cosine wave.

Re-run the simulation with "UIC" added to the .tran statement (.tran 50ms
uic) and see what it shows.  Using UIC forces the initial voltage to be 0V
at time=0, the start of the simulation.  That's like having the switch
initially open.

Or if you don't like that, multiply the sources by a PWL waveform that
starts both voltages at 0V and then switches them on, a few milliseconds
into the simulation, with the appropriate phase.

Or use an actual switch.  LTspice has a switch element you could use.

I guarantee you, the case with the voltage switching on at the 0V point in
the voltage waveform, causes greater currents.

The smaller surge current happens when the source is connected at the
moment when the current i(t) would be 0A if it were a continuous waveform.
For an inductive load, this happens when the voltage v(t) would be +/- peak
(or near peak, for a real load which has both inductance and a little
resistance).  This condition also results in no surge, thus no L/R decay.

All of this might not be relevant to a mechanical system, where surge
current is caused by rotational inertia, rather than anything electrical.

Regards,
Andy
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[time-nuts] Commercial software defined radio for clock metrology

[Sherman, Jeffrey A. (Fed)]

Hello,

A recently published paper might be of interest to the time-nuts community. We 
studied how well an unmodified commercial software defined radio (SDR) 
device/firmware could serve in comparing high-performance oscillators and 
atomic clocks. Though we chose to study the USRP platform, the discussion 
easily generalizes to many other SDRs.

I understand that for one month, the journal allows for free electronic 
downloads of the manuscript at:
http://scitation.aip.org/content/aip/journal/rsi/87/5/10.1063/1.4950898
(Review of Scientific Instruments 87, 054711 (2016))

Afterwards, a preprint will remain available at:
http://arxiv.org/abs/1605.03505

There are commercial instruments available with SDR architecture 
under-the-hood, but they often cost many thousands of dollars per measurement 
channel. In contrast, commercial general-purpose SDRs scale horizontally and 
can cost <= $1k per channel. Unlike the classic dual-mixer time-difference 
(DMTD) approach, SDRs are frequency agile. The carrier-acceptance range is 
limited not by the sample clock rate but by the ADC's input bandwidth (assuming 
one allows for aliasing), which can be many times greater. This property is an 
important feature in considering the future measurement of optical clocks, 
often accomplished through a heterodyne beatnote (often at "practically any" 
frequency between ~1 MHz to 500 MHz) with a femtosecond laser frequency comb. 
At typical microwave clock frequencies (5 MHz, 10 MHz), we show that a stock 
SDR outperforms a purpose-built DMTD instrument.

Perhaps the biggest worry about the SDR approach is that fast ADCs are in 
general much noisier than the analog processing components in DMTD. However, 
quantization noise is at least amenable to averaging. As you all likely 
appreciate, what really limits high precision clock comparison is instrument 
stability. In this regard, the SDR's digital signal processing steps (frequency 
translation, sample rate decimation, and low-pass filtering) are at least 
perfectly stable and can be made sufficiently accurate.

We found that in the studied units the limiting non-stationary noise source was 
likely the aperture jitter of the ADC (the instability of the delay between an 
idealized sample trigger and actuation of the sample/hold circuitry). However, 
the ADC's aperture jitter appears highly common-mode in chips with a second 
"simultaneously-sampled" input channel, allowing for an order-of-magnitue 
improvement after channel-to-channel subtraction. For example, at 5 MHz, the 
SDR showed a time deviation floor of ~20 fs after just 10 ms of averaging; the 
aperture jitter specification was 150 fs. We also describe tests with maser 
signals lasting several days.

Best wishes,
Jeff Sherman, Ph.D.

National Institute of Standards & Technology
Time and Frequency Division (688)
325 Broadway / Boulder, CO 80305 / 303-497-3511
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Re: [time-nuts] Maser 0.7 nsec jumps solved

[Gerhard Hoffmann]

Am 25.05.2016 um 18:59 schrieb Mike Monett:


This analysis shows switching at 0V is the best option.


No, it doesn't. :-)

First, the single inductor does not represent a transformer; the second 
inductor

and the coupling declaration ( style: K1 L1 L2 0.99 or so) and the load are
missing.

The most important thing is that the Inductor is nonlinear which is not
represented in the model. If there has remained some magnetism in
the core from previous operation, the transformer won't be able to further
increase the magnetism as needed to induce an opposing voltage
in the primary winding. When the core saturates, the inductance
collapses and leaves only the copper resistance to limit the current.

The catastrophe builds up in the first 90 degrees of the source wave,
not right at the start.

In the simulation, the current at t=0 is at its maximum already when at
t=0 the input voltage is just switched on. You'd expect that from a
capacitor, never from an inductor.

The reason is that the simulation does not really start at t=0, but
much earlier. The simulator computes the conductance matrix,
applies the initial sources and waits until everything has calmed down.
That may require repeated recalculation of the matrix to respect
nonlinearities.

Your circuit must contain hidden resistors btw, otherwise the computation
of the initial condition at "t<=0" would result in numeric overflow
as required by an assumed initial DC voltage across an inductor, before
the transient simulation.

One can enforce initial conditions with statements like  .IC v(my_node) = 0V

regards, Gerhard


BTW I've got the first 20 pcs. of the VCXO carrier / voltage regulator /
lock to reference / squarer / iso amp or frequency doubler / 1pps board.
That won't be soldering for beginners or jittery hands.  :-)






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Re: [time-nuts] I thought GPS repeated every 12 hours (-2 minutes)

[Attila Kinali]

On Wed, 25 May 2016 09:59:33 -0500
David  wrote:

> I was designed as a transmitter hunting antenna sacrificing size and
> gain for minimum side lobes.  You can see a photo of it on the front
> cover of October 1995 73 magazine.

For those who are also wondering what it looks like:
https://archive.org/details/73-magazine-1995-10

Attila Kinali

-- 
Reading can seriously damage your ignorance.
-- unknown
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Re: [time-nuts] Maser 0.7 nsec jumps solved

[Orin Eman]

On Wed, May 25, 2016 at 9:59 AM, Mike Monett 
wrote:

> >Am 23.05.2016 um 05:15 schrieb Jim Palfreyman:
> >> As far as a remedy goes we are going to try a solid state relay that
> only
> >> switches on at 0V in the AC waveform. This should slow the inrush
> current,
> >> and hopefully the magnetic impulse.
> >
> >In the context of transformers and motors, switching on at 0V is
> >actually the worst point in time.
> >
> >< https://de.wikipedia.org/wiki/Einschalten_des_Transformators > (German)
> >
> ><
> >
> http://electrical-engineering-portal.com/practical-considerations-of-transformer-inrush-current
> > >
> >
> >regards, Gerhard
>
> LTspice shows  switching  at 0V is the best point in  time.  With no
> flux in the magnetics, the inrush current is limited by  the circuit
> resistance. The magnitude is given by Ohm's law: I = E / R.
>
> Switching at 0V,
>
> I = E / R
> = 0 / R
> = 0A
>
> However, switching  at  the peak of the voltage can  give  very high
> inrush currents. You can verify this with LTspice. The  schematic is
> at
>
> http://www.pst.netii.net/misc/48b961a6.gif
>
> There are two circuits. They are identical except the second has the
> applied voltage  shifted  by 90 degrees. The  inductors  have  1 Ohm
> series resistance (not shown.)
>
> The waveforms are at
>
> http://www.pst.netii.net/misc/48b96217.gif
>
> The currents are IL1 and IL2.
>
> Switching at  0V, IL1 starts at zero. It rises to a  peak  of 900mA,
> then falls  back  to  zero. The DC offset takes 3  or  4  seconds to
> decay, then the current is stable at zero +/- 450mA.
>
> Switching at the peak, IL2 is
>
> I = E / R
> = 169.7 / 1
> = 169.7A
>


Er, no.  It's an RL circuit for which:

V(R) = E(1-e^(-(R/L)t)

so I(R) = I(L) = (E/R)(1-e^(-(R/L)t)

for t close to zero where E is essentially constant, I is going to rise
with the time constant of R/L which for a 1H inductor and 1 ohm resistance
is 1 second.

I suggest running the simulation with a pulse voltage source, Tdelay 1ms,
period 1s, Ton 0.5s (Period and Ton are fairly arbitrary, the Tdelay is
important).

You only need to run the simulation for a few ms.  You will get a very
different result.

Now as Poul-Henning Kamp suggested, an induction motor is anything but an
ideal inductor...
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Re: [time-nuts] HP5065A environmental sensitivities

[Angus]

Hi Corby,

That was really what I was hoping for from the small Rb's too, but
there appears to be other things at work with them.

I had not really considered that they might be sealed, but it's
something to look at. I had been thinking more about how it was fixed
into the package and with what materials. As well as the normal
component and circuit issues, there are also some deliberate ones like
discrete steps in temp correction which all add to the fun and
confusion.

BTW, if anyone has or knows of any pictures of a teardown of a FRK or
LPRO physics package, I'd be very interested.

Anyway, it's good to see that the 5065A is better behaved - I'm just
more jealous now! I look forward to seeing the results of your tests.

Angus.


On Sun, 22 May 2016 08:58:16 -0700, you wrote:

>Angus,
> 
>The HP 5065A has a fairly open path from atmosphere to the cells as far a
>barometric pressure is concerned.
>Response is rapid to a change.
> 
>The mechanism is "oil-canning" of the windows on the ends of the cell.
>Depends on diameter of the cell, thickness of the windows, and stiffness
>of the particular glass used. (for a particular gas mix of course)
> 
>It is VERY repeatable, and VERY linear.
> 
>I have heard that one European observatory routinely tracks the
>barometric pressure by watching their 5065A shift.
> 
>After seeing Wulf's data I can believe it!
> 
>My circuit is eliminating that variable quite nicely. As others have
>said, temperature will be a different matter.
> 
>I'm currently doing temperature tests and plan to eliminate the major
>causes rather than compensate.
> 
>Early measurements show as-built to be better than the spec of
>1.6X10-12/degree C.
> 
>Cheers,
> 
>Corby
>
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Re: [time-nuts] Simple solution for disciplining OCXO with 1 PPS

[Bernd Neubig]

Hi fellow time-nuts,
sorry for keeping quiet after having dropped my question. I was busy travelling 
an since yesterday our booth at the IMS2016/MTT keeps me busy too.
I will answer to the various comments as soon as I got some more quiet minutes.
I look forward to see many time-nuts this afternoon at 5:00 pm at the Dynamic 
Engineers booth #714

Bernd

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Re: [time-nuts] I thought GPS repeated every 12 hours (-2 minutes)

[David]

On Wed, 25 May 2016 19:33:37 +0200, you wrote:

>
>> Le 25 mai 2016 à 16:59, David  a écrit :
>> 
>> I was designed as a transmitter hunting antenna sacrificing size and
>> gain for minimum side lobes. 
>
>I’ve got to see your selfie.  

It was not a selfie.  Joe Moell, K0OV, took the photograph on the
monthly Catalina Transmitter Hunt and without me knowing, submitted it
to 73.

When I was working through various antenna designs, that is the one I
stopped at because we had no way to test anything better; the side
lobes where lower than the reflections at our antenna test range which
was as barren a parking lot on top of a hill that we could find.
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Re: [time-nuts] I thought GPS repeated every 12 hours (-2 minutes)

[Mike Cook]

> Le 25 mai 2016 à 16:59, David  a écrit :
> 
> I was designed as a transmitter hunting antenna sacrificing size and
> gain for minimum side lobes. 

I’ve got to see your selfie.  


"The power of accurate observation is commonly called cynicism by those who 
have not got it. »
George Bernard Shaw

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Re: [time-nuts] Maser 0.7 nsec jumps solved

[Poul-Henning Kamp]

In message , "Mike Monett" writes:

>The wikipedia  article  states "To avoid magnetic  inrush,  only for
>transformers with  an air gap in the core, the inductive  load needs
>to be synchronously connected near a supply voltage peak."

You ought to have stopped and wondered at the "with an air gap in the core"
and pondered if you SPICE models use of an ideal inductor was appropriate
for something as electrically complex as an induction motor...

-- 
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.
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Re: [time-nuts] Maser 0.7 nsec jumps solved

[Mike Monett]

>Am 23.05.2016 um 05:15 schrieb Jim Palfreyman:
>> As far as a remedy goes we are going to try a solid state relay that only
>> switches on at 0V in the AC waveform. This should slow the inrush current,
>> and hopefully the magnetic impulse.
>
>In the context of transformers and motors, switching on at 0V is
>actually the worst point in time.
>
>< https://de.wikipedia.org/wiki/Einschalten_des_Transformators > (German)
>
><
>http://electrical-engineering-portal.com/practical-considerations-of-transformer-inrush-current
> >
>
>regards, Gerhard

LTspice shows  switching  at 0V is the best point in  time.  With no
flux in the magnetics, the inrush current is limited by  the circuit
resistance. The magnitude is given by Ohm's law: I = E / R.

Switching at 0V,

I = E / R
= 0 / R
= 0A

However, switching  at  the peak of the voltage can  give  very high
inrush currents. You can verify this with LTspice. The  schematic is
at

http://www.pst.netii.net/misc/48b961a6.gif

There are two circuits. They are identical except the second has the
applied voltage  shifted  by 90 degrees. The  inductors  have  1 Ohm
series resistance (not shown.)

The waveforms are at

http://www.pst.netii.net/misc/48b96217.gif

The currents are IL1 and IL2.

Switching at  0V, IL1 starts at zero. It rises to a  peak  of 900mA,
then falls  back  to  zero. The DC offset takes 3  or  4  seconds to
decay, then the current is stable at zero +/- 450mA.

Switching at the peak, IL2 is

I = E / R
= 169.7 / 1
= 169.7A

It takes over twice as long for the starting surge to decay. I could
still detect it past 8 seconds.

This analysis shows switching at 0V is the best option.

If you wish to do further analysis, the LTspice .ASC and  .PLT files
are at

http://www.pst.netii.net/misc/48b96262.zip

The wikipedia  article  states "To avoid magnetic  inrush,  only for
transformers with  an air gap in the core, the inductive  load needs
to be synchronously connected near a supply voltage peak."

https://en.wikipedia.org/wiki/Inrush_current

Clearly, from  the  above LTspice waveforms, switching  at  the peak
gives the  highest inrush surge that is possible to obtain.  It also
takes the longest time to decay.

MRM
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Re: [time-nuts] I thought GPS repeated every 12 hours (-2 minutes)

[David]

On Wed, 25 May 2016 06:34:46 -0700, you wrote:

>On 5/24/2016 7:26 PM, David wrote
>>The 2 meter
>> directional antenna I ultimately designed was good enough to not only
>> track airlines by their reflected RF, but it could see reflections and
>> shadows from nearby objects like street lights and trees which
>> ultimately limited outside performance testing.
>
>As someone who operated amateur radio moonbounce on 2-meters back in the day 
>when you actually had to hear the signals, I find this really hard to believe.
>
>Wes  N7WS

I was designed as a transmitter hunting antenna sacrificing size and
gain for minimum side lobes.  You can see a photo of it on the front
cover of October 1995 73 magazine.
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[time-nuts] Operational experience with NTP's symmetric mode?

[Sharon Goldberg]

As part of the IETF Network Time Security (NTS) effort, it would be helpful
to understand the importance of NTP's symmetric peering mode.  Can folks on
this list please share their experience with NTP's symmetric mode?

Do you use it, and if so why (or why not), and if so in what operational
environment are you using it?

Active/active or active/passive?  Crypto authentication or not?

Thank you,
Sharon (For NTS design team)

-- 
Sharon Goldberg
Computer Science, Boston University
http://www.cs.bu.edu/~goldbe
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Re: [time-nuts] I thought GPS repeated every 12 hours (-2 minutes)

[Wes]

On 5/24/2016 7:26 PM, David wrote

   The 2 meter
directional antenna I ultimately designed was good enough to not only
track airlines by their reflected RF, but it could see reflections and
shadows from nearby objects like street lights and trees which
ultimately limited outside performance testing.
As someone who operated amateur radio moonbounce on 2-meters back in the day 
when you actually had to hear the signals, I find this really hard to believe.


Wes  N7WS
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Re: [time-nuts] I thought GPS repeated every 12 hours (-2 minutes)

[Don Lewis]

Still do, to this day!

With my OTA HD TV and living in the vicinity of ABIA in Austin, TX.

When the wind is out of the north, and they take off to the north darn 
planes!


Don
N5CID






-Original Message- 
From: billriches

Sent: Wednesday, May 25, 2016 5:34 AM
To: 'Discussion of precise time and frequency measurement'
Subject: Re: [time-nuts] I thought GPS repeated every 12 hours (-2 minutes)

Reminds me of the 1950's living in Wildwood, NJ.  We had a TV antenna on the 
roof to pick up stations from Philadelphia - 80 miles away.  When ever an 
airplane flew over you would see flutter and distorted sound!


73,

Bill, WA2DVU
Cape May

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Re: [time-nuts] I thought GPS repeated every 12 hours (-2 minutes)

[Bob Camp]

Hi

Multipath on GPS normally requires a couple of things:

1) The satellite you are trying to lock on to needs to be obscured. Being below 
the 
local horizon is one normal way for this to happen. 

2) The satellite signal needs to be reflected off of something that does not 
put in enough 
dopler to take it out of whatever the doppler correction “stuff” is happy with 

3) The signal path length has to be close enough that the normal firmware does 
not reject
the solution. 

4) The reflected signal has to be strong enough to be out of the noise in the 
normal demodulation
bandwidths. This includes odd things like polarization. 

5) The geometry between the objects (sat included) has to hold long enough for 
it to contribute to 
a multi second solution. Anything below a few seconds is normally rejected by 
the GPSDO firmware. 

I’m sure there are a few other qualifiers. Bottom line is that it’s easier to 
get multi path off of a 
stationary object. A shallow angle fixed geometry setup can give you a problem 
for quite a while. 

Bob



> On May 24, 2016, at 10:26 PM, David  wrote:
> 
> On Tue, 24 May 2016 16:15:15 -0700, you wrote:
> 
>> 
>> kb...@n1k.org said:
>>> The glitches are to narrow (short duration) and far to regular for the
>>> ionosphere to be the issue.  
>> 
>> Is multipath from a large airliner in a landing pattern likely to cause that 
>> sort of problems?
>> 
>> I'm 20+ miles off the end of SFO, but it's common to see large planes going 
>> over and turning to line up for a landing.  On my one-of-these-days list is 
>> to grab the airline location data and see if it correlates with GPS glitches.
> 
> Back when I did a lot of transmitter hunting, I listened to multipath
> from airliners from 2 meters to 23 centimeters.  The 2 meter
> directional antenna I ultimately designed was good enough to not only
> track airlines by their reflected RF, but it could see reflections and
> shadows from nearby objects like street lights and trees which
> ultimately limited outside performance testing.
> 
> As you can calculate from the geometry, the flutter started out fast
> and decreased in frequency until there was a slow null/peak and then
> it reversed.  If the same happened with GPS, then maybe the receiver
> could briefly lock onto the reflection from the plane producing a
> different solution for a short time.
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Re: [time-nuts] I thought GPS repeated every 12 hours (-2 minutes)

[billriches]

Reminds me of the 1950's living in Wildwood, NJ.  We had a TV antenna on the 
roof to pick up stations from Philadelphia - 80 miles away.  When ever an 
airplane flew over you would see flutter and distorted sound!

73,

Bill, WA2DVU
Cape May

-Original Message-
From: time-nuts [mailto:time-nuts-boun...@febo.com] On Behalf Of David
Sent: Tuesday, May 24, 2016 10:26 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] I thought GPS repeated every 12 hours (-2 minutes)

On Tue, 24 May 2016 16:15:15 -0700, you wrote:

>
>kb...@n1k.org said:
>> The glitches are to narrow (short duration) and far to regular for 
>> the ionosphere to be the issue.
>
>Is multipath from a large airliner in a landing pattern likely to cause 
>that sort of problems?
>
>I'm 20+ miles off the end of SFO, but it's common to see large planes 
>going over and turning to line up for a landing.  On my 
>one-of-these-days list is to grab the airline location data and see if it 
>correlates with GPS glitches.

Back when I did a lot of transmitter hunting, I listened to multipath from 
airliners from 2 meters to 23 centimeters.  The 2 meter directional antenna I 
ultimately designed was good enough to not only track airlines by their 
reflected RF, but it could see reflections and shadows from nearby objects like 
street lights and trees which ultimately limited outside performance testing.

As you can calculate from the geometry, the flutter started out fast and 
decreased in frequency until there was a slow null/peak and then it reversed.  
If the same happened with GPS, then maybe the receiver could briefly lock onto 
the reflection from the plane producing a different solution for a short time.
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Re: [time-nuts] Nuclear transition for time reference - Nature 5-May, 2016, vol 533

[Attila Kinali]

On Mon, 23 May 2016 11:49:37 -0500
David Witten  wrote:

> My knowledge in this area is superficial.  But I wondered if anyone in this
> group had a reaction to the 5-May issue of nature that includes a 'News and
> Views' piece and a formal article reporting the detection by Von der Wense
> et al. of the 229m Thorium nuclear transition that is hoped to have utility
> in time-related metrology applications?
> 
> The key point seems to be that since nuclear transitions of this sort
>  involve shifts among excited states by quarks, which are governed by the
> strong force, many of the electromagnetic perturbations of clocks governed
> by electromagnetic force are eliminated.  (I think.)

Not only that. Because the nucleus is shielded by the electronic shell
from other atoms it's also less disturbed by anything close by.
While our current clocks all measure the hyperfine splitting (aka interaction
of the electron orbit angular momentum with the nuclear spin) of the
outermost electron, which is the one that gets hit first if anything in
the vincinity of the atom happens.

One of the problems seems to be, that the transistion is either very narrow,
or not where people expect it. This experiment (if the conclusions are
correct) narrowed down the range where the transition should be.
It's still far from actually detecting the transition, but at least it's
a good step forward.


Attila Kinali
-- 
Reading can seriously damage your ignorance.
-- unknown
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Re: [time-nuts] Simple solution for disciplining OCXO with 1 PPS

[David J Taylor]

From: Wes

A cleaver design, but the OP wanted 1pps.  I have the Leo Bodnar GPSDO.  It 
too

is a nice frequency standard, but it doesn't know what time it is.
=

This box can do either 10 MHz or 1 PPS.

 http://leontp.com/

"Coming soon"

Cheers,
David
--
SatSignal Software - Quality software written to your requirements
Web: http://www.satsignal.eu
Email: david-tay...@blueyonder.co.uk
Twitter: @gm8arv 


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