Re: [time-nuts] RG6 or LMR400 for GPS Antenna (Symmetricom 58532A and T-bolt)

[Bruce Lane]

My $0.02 worth.

If the cable is going to be exposed to sunlight and weather, long-term,
be sure you get a cable type rated for UV exposure (polyethylene
jacketed). If you really want to get something rugged, and you don't
mind removing a bit of citrus-scented goo, go with 'DB' (Direct Burial)
suffixed cable (Example: LMR400DB).

Whatever you do, DON'T use the cheap PVC-jacketed cable! Sunlight eats
that stuff for breakfast.

Happy tweaking.


On 20-Apr-16 18:03, Ryan Stasel wrote:
> Bob/Paul,
> 
> Thanks. And there's the rub... Who knows what the specs are on "generic" RG6 
> QS. I'll see what my seller wants for their LMR400, but otherwise yeah, RG6 
> is just easier. I have both compression and crimp connectors for it, 
> including some RG6 N-connectors (yeah, they're probably for LMR300, but they 
> work). 
> 
> Other question: any tips for the exterior N connection? I can "weatherproof" 
> the actual cable-connector crimp, but I'm curious if anyone bothers to "lube" 
> the N connector to keep moisture from otherwise seizing it up. 
> 
> Thanks!
> 
> Ryan Stasel
> IT Operations Manager, SOJC
> University of Oregon
> 
> Sent from my iPhone
> 

(Snipped to save space).

-- 
---
Bruce Lane, ARS KC7GR
http://www.bluefeathertech.com
kyrrin (at) bluefeathertech dot com
"Quando Omni Flunkus Moritati" (Red Green)
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Re: [time-nuts] RG6 or LMR400 for GPS Antenna (Symmetricom 58532A and T-bolt)

[Rob Sherwood .]

I purchases NOS 3/8th inch hardline for my GPS antenna run.  It had factory 
installed N connectors on it, so all I needed was an N to TNC adapter on the 
receiver end of my Trak GPSDO. Rob, NC0B.  

Sent from my iPad

> On Apr 20, 2016, at 6:00 PM, "Bob Camp"  wrote:
> 
> 
> 
> Hi
> 
> RG-6 Quad Shield should be fine as long as it’s meeting the published specs. 
> The advantage of LRM-400 is that you likely *know* where it came from and 
> what the specs are. 
> 
> If you decide to split the antenna between GPSDO’s, a powered splitter is a 
> really good idea. Each time you split another 2 ways, you loose 3 db. Get at 
> least a 4 way splitter ….
> 
> Bob
> 
>> On Apr 20, 2016, at 4:41 PM, Ryan Stasel  wrote:
>> 
>> All, 
>> 
>> I’m going to be installing a “permanent” antenna at home, and will need a 
>> run of about 100ft to get from my workstation, to the mast I’ll be mounting 
>> the antenna on (Symmetricom 58532A). I’ve seen some indication that both the 
>> antenna and the Trimble Thunderbolt won’t have any issues with running over 
>> 75ohm cable, but thought I’d ask the “experts” whether I’d be better off 
>> with some RG6 Quad-shield, or LMR400 (I’ve got a local source that doesn’t 
>> know what LMR400 is, or what it’s worth)? 
>> 
>> Obviously I’d prefer to run and crimp RG6, but if I’d be better off with 
>> LMR400, I’d rather run that now than go back into the crawlspace again. =)
>> 
>> Also, if it helps, I’ll probably have a Symmetricom/HP 58516A at/near the 
>> T-bolt so I can experiment with other GPS(DO)s as well (especially one of 
>> the JRMiller boards I bought and built (but never finished) ages ago). Which 
>> brings the question, will the T-bolt provide the oomph needed to power that 
>> splitter and the antenna over that length of cable? 
>> 
>> Thanks! 
>> 
>> -Ryan Stasel
>> 
>> 
>> ___
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Re: [time-nuts] RG6 or LMR400 for GPS Antenna (Symmetricom 58532A and T-bolt)

[Pete Stephenson]

On Wed, Apr 20, 2016 at 10:41 PM, Ryan Stasel  wrote:
> All,
>
> I’m going to be installing a “permanent” antenna at home, and will need a run 
> of about 100ft to get from my workstation, to the mast I’ll be mounting the 
> antenna on (Symmetricom 58532A). I’ve seen some indication that both the 
> antenna and the Trimble Thunderbolt won’t have any issues with running over 
> 75ohm cable, but thought I’d ask the “experts” whether I’d be better off with 
> some RG6 Quad-shield, or LMR400 (I’ve got a local source that doesn’t know 
> what LMR400 is, or what it’s worth)?
>
> Obviously I’d prefer to run and crimp RG6, but if I’d be better off with 
> LMR400, I’d rather run that now than go back into the crawlspace again. =)

I'm hardly an expert, but according to the Times Microwave calculator
at , RG6 (of unspecified
type, presumably double not quad-shielded) at 1542MHz will have a loss
of 12dB over a 100ft length. LMR400 will have a loss of 5.2dB over
that same length.

The datasheet for your specific cable should show the loss figures.

The 58532A has an amplifier with a gain of >30dB, so it should work
well even at moderate cable lengths.

Keep in mind that the Thunderbolt Starter kit came with a Trimble
Bullet antenna (similar gain to the 58532A) and 75 feet of RG6; it'll
almost certainly work fine with 100ft of cable: the manual for the
Thunderbolt recommends RG-59 cable (presumably because it's cheap and
common) and states "The maximum practical cable run is just over 100
feet." A graph in the manual shows RG-59 losing 15dB over 100ft,

To be safe, you could always test it by connecting the 100ft of cable
to the antenna and putting it outside in a more convenient location
that has a similar view as your mast and seeing how the Thunderbolt
likes it.

Also, keep in mind that the 58516A splitter can have between +3 and -3
dB of gain depending on your luck as to how it was made. The manual
says that for relatively lossy RG-213 cable and the worst case
performance of the 58516A, you should be fine with up to 174 feet of
cable with no line amplifier.

> Also, if it helps, I’ll probably have a Symmetricom/HP 58516A at/near the 
> T-bolt so I can experiment with other GPS(DO)s as well (especially one of the 
> JRMiller boards I bought and built (but never finished) ages ago). Which 
> brings the question, will the T-bolt provide the oomph needed to power that 
> splitter and the antenna over that length of cable?

Short answer: Yes.

Longer answer: The Thunderbolt manual says it can supply 5V at up to
45mA. The 58532A antenna draws a max of 27mA (with 20mA being
typical). The 58516A splitter manual draws it uses 10mA. Worst case
usage is 37mA, which is within the limits for the Thunderbolt.

Considering both conductors, 100ft of LMR400 has a DC resistance of
0.304 ohms, so the voltage drop would only be 0.01V over that length.
That's well within specs for the antenna (5V +/- 0.5V) and the
splitter (4.5 to 30V).

The specs for Belden 1189AP quad-shield RG6/U cable with a copper-clad
steel center conductor and aluminum braid lists the total resistance
for both conductors to be 3.28 ohms over 100 feet. That's a worst-case
voltage drop of 0.12V over that distance, again within spec for both
devices.

In short, LMR400 would be a better choice in terms of both signal
attenuation and DC resistance, but the difference is more or less
academic and either cable should work fine.

Cheers!
-Pete

-- 
Pete Stephenson
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Re: [time-nuts] RG6 or LMR400 for GPS Antenna (Symmetricom 58532A and T-bolt)

[bownes]

N connectors should never need to 'lubed'. Properly assembled they are 
waterproof. Same goes for BNC. That's what the rubber gasket on the mating 
surface is for. Metrology grade Ns don't have the gasket but you shouldn't need 
it on your metrology bench. :)

That being said, it never hurts to wrapped up with coax seal tape. 

> On Apr 20, 2016, at 21:03, Ryan Stasel  wrote:
> 
> Bob/Paul,
> 
> Thanks. And there's the rub... Who knows what the specs are on "generic" RG6 
> QS. I'll see what my seller wants for their LMR400, but otherwise yeah, RG6 
> is just easier. I have both compression and crimp connectors for it, 
> including some RG6 N-connectors (yeah, they're probably for LMR300, but they 
> work). 
> 
> Other question: any tips for the exterior N connection? I can "weatherproof" 
> the actual cable-connector crimp, but I'm curious if anyone bothers to "lube" 
> the N connector to keep moisture from otherwise seizing it up. 
> 
> Thanks!
> 
> Ryan Stasel
> IT Operations Manager, SOJC
> University of Oregon
> 
> Sent from my iPhone
> 
>> On Apr 20, 2016, at 17:00, Bob Camp  wrote:
>> 
>> Hi
>> 
>> RG-6 Quad Shield should be fine as long as it’s meeting the published specs. 
>> The advantage of LRM-400 is that you likely *know* where it came from and 
>> what the specs are. 
>> 
>> If you decide to split the antenna between GPSDO’s, a powered splitter is a 
>> really good idea. Each time you split another 2 ways, you loose 3 db. Get at 
>> least a 4 way splitter ….
>> 
>> Bob
>> 
>>> On Apr 20, 2016, at 4:41 PM, Ryan Stasel  wrote:
>>> 
>>> All, 
>>> 
>>> I’m going to be installing a “permanent” antenna at home, and will need a 
>>> run of about 100ft to get from my workstation, to the mast I’ll be mounting 
>>> the antenna on (Symmetricom 58532A). I’ve seen some indication that both 
>>> the antenna and the Trimble Thunderbolt won’t have any issues with running 
>>> over 75ohm cable, but thought I’d ask the “experts” whether I’d be better 
>>> off with some RG6 Quad-shield, or LMR400 (I’ve got a local source that 
>>> doesn’t know what LMR400 is, or what it’s worth)? 
>>> 
>>> Obviously I’d prefer to run and crimp RG6, but if I’d be better off with 
>>> LMR400, I’d rather run that now than go back into the crawlspace again. =)
>>> 
>>> Also, if it helps, I’ll probably have a Symmetricom/HP 58516A at/near the 
>>> T-bolt so I can experiment with other GPS(DO)s as well (especially one of 
>>> the JRMiller boards I bought and built (but never finished) ages ago). 
>>> Which brings the question, will the T-bolt provide the oomph needed to 
>>> power that splitter and the antenna over that length of cable? 
>>> 
>>> Thanks! 
>>> 
>>> -Ryan Stasel
>>> 
>>> 
>>> ___
>>> 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.
>> 
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Re: [time-nuts] RG6 or LMR400 for GPS Antenna (Symmetricom 58532A and T-bolt)

[William H. Fite]

I've gotten some very poor quality RG6 in the past, despite having
purchased it from ostensibly reputable sources. Now I use
honest-to-goodness Times Microwave LMR400.

I have terminated LMR400 with BNC, PL259, SO239, and N connectors and never
had one fail. It is not at all difficult to do.

"The bitterness of poor quality remains long after the sweetness of low
price has been forgotten."

Bill


On Wednesday, April 20, 2016, Bob Camp  wrote:

> Hi
>
> RG-6 Quad Shield should be fine as long as it’s meeting the published
> specs. The advantage of LRM-400 is that you likely *know* where it came
> from and what the specs are.
>
> If you decide to split the antenna between GPSDO’s, a powered splitter is
> a really good idea. Each time you split another 2 ways, you loose 3 db. Get
> at least a 4 way splitter ….
>
> Bob
>
> > On Apr 20, 2016, at 4:41 PM, Ryan Stasel  > wrote:
> >
> > All,
> >
> > I’m going to be installing a “permanent” antenna at home, and will need
> a run of about 100ft to get from my workstation, to the mast I’ll be
> mounting the antenna on (Symmetricom 58532A). I’ve seen some indication
> that both the antenna and the Trimble Thunderbolt won’t have any issues
> with running over 75ohm cable, but thought I’d ask the “experts” whether
> I’d be better off with some RG6 Quad-shield, or LMR400 (I’ve got a local
> source that doesn’t know what LMR400 is, or what it’s worth)?
> >
> > Obviously I’d prefer to run and crimp RG6, but if I’d be better off with
> LMR400, I’d rather run that now than go back into the crawlspace again. =)
> >
> > Also, if it helps, I’ll probably have a Symmetricom/HP 58516A at/near
> the T-bolt so I can experiment with other GPS(DO)s as well (especially one
> of the JRMiller boards I bought and built (but never finished) ages ago).
> Which brings the question, will the T-bolt provide the oomph needed to
> power that splitter and the antenna over that length of cable?
> >
> > Thanks!
> >
> > -Ryan Stasel
> >
> >
> > ___
> > 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.
>
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>


-- 
Sent from Gmail Mobile
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Re: [time-nuts] RG6 or LMR400 for GPS Antenna (Symmetricom 58532A and T-bolt)

[Ryan Stasel]

Bob/Paul,

Thanks. And there's the rub... Who knows what the specs are on "generic" RG6 
QS. I'll see what my seller wants for their LMR400, but otherwise yeah, RG6 is 
just easier. I have both compression and crimp connectors for it, including 
some RG6 N-connectors (yeah, they're probably for LMR300, but they work). 

Other question: any tips for the exterior N connection? I can "weatherproof" 
the actual cable-connector crimp, but I'm curious if anyone bothers to "lube" 
the N connector to keep moisture from otherwise seizing it up. 

Thanks!

Ryan Stasel
IT Operations Manager, SOJC
University of Oregon

Sent from my iPhone

> On Apr 20, 2016, at 17:00, Bob Camp  wrote:
> 
> Hi
> 
> RG-6 Quad Shield should be fine as long as it’s meeting the published specs. 
> The advantage of LRM-400 is that you likely *know* where it came from and 
> what the specs are. 
> 
> If you decide to split the antenna between GPSDO’s, a powered splitter is a 
> really good idea. Each time you split another 2 ways, you loose 3 db. Get at 
> least a 4 way splitter ….
> 
> Bob
> 
>> On Apr 20, 2016, at 4:41 PM, Ryan Stasel  wrote:
>> 
>> All, 
>> 
>> I’m going to be installing a “permanent” antenna at home, and will need a 
>> run of about 100ft to get from my workstation, to the mast I’ll be mounting 
>> the antenna on (Symmetricom 58532A). I’ve seen some indication that both the 
>> antenna and the Trimble Thunderbolt won’t have any issues with running over 
>> 75ohm cable, but thought I’d ask the “experts” whether I’d be better off 
>> with some RG6 Quad-shield, or LMR400 (I’ve got a local source that doesn’t 
>> know what LMR400 is, or what it’s worth)? 
>> 
>> Obviously I’d prefer to run and crimp RG6, but if I’d be better off with 
>> LMR400, I’d rather run that now than go back into the crawlspace again. =)
>> 
>> Also, if it helps, I’ll probably have a Symmetricom/HP 58516A at/near the 
>> T-bolt so I can experiment with other GPS(DO)s as well (especially one of 
>> the JRMiller boards I bought and built (but never finished) ages ago). Which 
>> brings the question, will the T-bolt provide the oomph needed to power that 
>> splitter and the antenna over that length of cable? 
>> 
>> Thanks! 
>> 
>> -Ryan Stasel
>> 
>> 
>> ___
>> 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.
> 
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Re: [time-nuts] Adapting my GPSDO to the FE-5680A

[Bob Camp]

Hi

Most of these telco Rb’s start out around 2x10^-11 at 1 second tau. Their ADEV 
then drops
as square root of tau. At 100 seconds they hit 2x10^-12 and at 10,000 seconds 
they (might) 
hit 2x10^-13. A *good* OCXO will do 2x10^-12 at 100 seconds. An excellent part 
will hold
sub 1x10^-12 out to 1,000 seconds.

Very roughly speaking the Rb will beat out the OCXO somewhere past 100 seconds 
and somewhere 
before  1,000 seconds. 

Bob

> On Apr 20, 2016, at 6:31 PM, Nick Sayer via time-nuts  
> wrote:
> 
> Thanks. I’ve taken your suggestion for the sine-to-square converter.
> 
> I believe there are two separate commands for tuning the 5680 - one is 
> “temporary” and one writes through to the EEPROM. I’ll be using the latter, 
> of course.
> 
> http://www.ka7oei.com/10_MHz_Rubidium_FE-5680A.html
> 
> I do agree that the short term stability of the 5680A isn’t as good as an 
> OCXO, but at tau ~2s or so, the tables are turned. I’m getting a good measure 
> of my undisciplined 5680A as we speak to get a good control, but it’s 
> difficult, as I’m testing it against a Thunderbolt, and I think I’m seeing 
> its “hump” (http://www.leapsecond.com/pages/gpsdo/) from 10s to 300s coming 
> through. In any event, I’m getting awfully close to the limits of my 53220a. 
> I may go down the road of trying to make a mash-up as you suggest, but I’m 
> going to start by seeing if I can give myself a choice between whether I want 
> short term stability (OCXO) or medium term (Rubidium) for my reference.
> 
> 
>> On Apr 20, 2016, at 1:57 PM, Attila Kinali  wrote:
>> 
>> On Wed, 20 Apr 2016 07:17:58 -0700
>> Nick Sayer via time-nuts  wrote:
>> 
>>> I spent some time yesterday mashing together my FE-5680A "breakout" board 
>>> with my GPSDO to make a GPS discipline board for it. Before I send the 
>>> board 
>>> off to OSHPark, I'd like to open the design to criticism (and I mean that 
>>> in 
>>> its neutral sense) here first.
>> 
>> Looking at your schematics, I would replace the input squarer (IC4)
>> by something different than a schmitt-trigger with an input bias
>> voltage. For one, schmitt-triggers are more noisy than normal buffers
>> for an other, the bias voltage will result in a slightly skewed duty
>> cycle. If you want to use a gate, then the canoncical way would be to
>> use an inverter with an input capacitor like you did, but let it self-bias
>> itself by using a 100k-1M resistor from its output to its input.
>> Important: don't use a buffer, as this will only work with an inverter.
>> But I'd rather use a different squaring circuit, if you want to use
>> the input directly for the output. There are many discussions on
>> squaring circuits in the archives. Probably the most simple, yet sofisticated
>> is the one you can find in the TADD-2.
>> 
>> 
>> But:
>> As you can see on http://www.ke5fx.com/rb.htm the phase noise of the
>> FE 5680's is horrible at best, hence I wouldn't use it as source for
>> anything directly. Additionally, the tuning word you write through
>> the RS-232 is stored in an EEPROM inside the FE-5860 (unless i mix
>> it up with another Rb). Writing this tuning word often will wear out
>> the EEPROM pretty quickly. Hence you should not do this too often.
>> 
>> What I would do instead is, use your current GPSDO design, with OCXO
>> and all, but add something with which you can measure the phase/frequency
>> of an external 10MHz reference. One way would be to use a digital DMTD[1,2].
>> Another would be to sample the reference using an ADC and build DMTD in
>> the digital domain. For this you wouldn't need a high sampling rate, a
>> couple of kHz should be enough, as long as the analog bandwidth of the
>> ADC is high enough (>10MHz, better >20MHz). What you need is some PLL
>> though, as you need to create a frequency that is not an integer divisible
>> of 10MHz, as the ADC clock is used to downmix the reference frequency.
>> 
>> Eg:
>> If you can generate a 10001Hz ADC sampling clock from the OCXO,
>> you will get a 1kHz beat frequency. You can "lock" to this using a
>> digital PLL combined with an NCO (numerically controlled oscillator).
>> Then use the steering word for the NCO as an input for the control
>> loop of the OCXO, toghether with the corrections calculated from the
>> GPS PPS.
>> 
>> The advantage of this is, that you get the low phase noise and good
>> short term stability of the OCXO, but can use the Rb to get the nice
>> mid-term stability (somewhere from 1 to 10s up) while getting the
>> accuracy of a GPSDO, whithout ever the need of writing to the tuning
>> word of the Rb. That keeps your Rb more stable (the internal conditions
>> of the Rb do not change) and allows you to compensate for quite large
>> frequency offsets for Rb refernces that are working outside the spec,
>> but are otherwise fine.
>> 
>> One thing that you have to take care of is spurs, though. Because
>> the ADC does some heavy down-mixing, or rather 

Re: [time-nuts] Adapting my GPSDO to the FE-5680A

[Bruce Griffiths]

Sampling at 4x(10MHz + 1kHz) followed by a digital image reject mixer would 
work better.The front end analog filter only needs to reject unwanted nyquist 
regions, thus it can have a wider bandwidth and low phase shift tempco. Its PN 
noise contribution can also be small. Digital filters can be used to reject the 
undesired spurs.

Bruce 

On Thursday, 21 April 2016 10:10 AM, Bruce Griffiths 
 wrote:
 

 There's the small matter of the high phase shift tempco of the narrow 10MHz 
bandpass filters Q~10,000 or so.These would need to either track very closely 
or be in an oven with very high temperature stability.The PN contribution of 
these analog filters may also be an issue.
 
Bruce

On Thursday, 21 April 2016 9:03 AM, Attila Kinali  wrote:
 

 On Wed, 20 Apr 2016 07:17:58 -0700
Nick Sayer via time-nuts  wrote:

> I spent some time yesterday mashing together my FE-5680A "breakout" board 
> with my GPSDO to make a GPS discipline board for it. Before I send the board 
> off to OSHPark, I'd like to open the design to criticism (and I mean that in 
> its neutral sense) here first.

Looking at your schematics, I would replace the input squarer (IC4)
by something different than a schmitt-trigger with an input bias
voltage. For one, schmitt-triggers are more noisy than normal buffers
for an other, the bias voltage will result in a slightly skewed duty
cycle. If you want to use a gate, then the canoncical way would be to
use an inverter with an input capacitor like you did, but let it self-bias
itself by using a 100k-1M resistor from its output to its input.
Important: don't use a buffer, as this will only work with an inverter.
But I'd rather use a different squaring circuit, if you want to use
the input directly for the output. There are many discussions on
squaring circuits in the archives. Probably the most simple, yet sofisticated
is the one you can find in the TADD-2.


But:
As you can see on http://www.ke5fx.com/rb.htm the phase noise of the
FE 5680's is horrible at best, hence I wouldn't use it as source for
anything directly. Additionally, the tuning word you write through
the RS-232 is stored in an EEPROM inside the FE-5860 (unless i mix
it up with another Rb). Writing this tuning word often will wear out
the EEPROM pretty quickly. Hence you should not do this too often.

What I would do instead is, use your current GPSDO design, with OCXO
and all, but add something with which you can measure the phase/frequency
of an external 10MHz reference. One way would be to use a digital DMTD[1,2]..
Another would be to sample the reference using an ADC and build DMTD in
the digital domain. For this you wouldn't need a high sampling rate, a
couple of kHz should be enough, as long as the analog bandwidth of the
ADC is high enough (>10MHz, better >20MHz). What you need is some PLL
though, as you need to create a frequency that is not an integer divisible
of 10MHz, as the ADC clock is used to downmix the reference frequency.

Eg:
If you can generate a 10001Hz ADC sampling clock from the OCXO,
you will get a 1kHz beat frequency. You can "lock" to this using a
digital PLL combined with an NCO (numerically controlled oscillator).
Then use the steering word for the NCO as an input for the control
loop of the OCXO, toghether with the corrections calculated from the
GPS PPS.

The advantage of this is, that you get the low phase noise and good
short term stability of the OCXO, but can use the Rb to get the nice
mid-term stability (somewhere from 1 to 10s up) while getting the
accuracy of a GPSDO, whithout ever the need of writing to the tuning
word of the Rb. That keeps your Rb more stable (the internal conditions
of the Rb do not change) and allows you to compensate for quite large
frequency offsets for Rb refernces that are working outside the spec,
but are otherwise fine.

One thing that you have to take care of is spurs, though. Because
the ADC does some heavy down-mixing, or rather sub-sampling, this
approach is quite sensitive to spurs. In order to not introduce some
weird oscillations in the control loop due to spurs in the reference
signal, you should use some narrow 10MHz filter at the input (at most
half the sampling frequency wide). One way to achieve that is using a
ceramic resonator which are available at 10MHz.

            Attila Kinali

PS: I'm pretty sure I am not the first one with this idea. But I have never
seen anyone else mention it, much less implement it. Does anyone know why?


[1] "Digital Dual Mixer Time Difference for Sub-Nanosecond Time
Synchronization in Ethernet", by Moreira, Alvares, Serrano, Darwezeh and
Wlostowski, 2010

[2] "Digital femtosecond time difference circuit for CERN's timing system",
by Moreira, Darwazeh, 2011
http://www.ee.ucl.ac.uk/lcs/previous/LCS2011/LCS1136.pdf

-- 
Reading can seriously damage your ignorance.
        -- unknown
___
time-nuts mailing list 

Re: [time-nuts] Adapting my GPSDO to the FE-5680A

[Nick Sayer via time-nuts]

Thanks. I’ve taken your suggestion for the sine-to-square converter.

I believe there are two separate commands for tuning the 5680 - one is 
“temporary” and one writes through to the EEPROM. I’ll be using the latter, of 
course.

http://www.ka7oei.com/10_MHz_Rubidium_FE-5680A.html

I do agree that the short term stability of the 5680A isn’t as good as an OCXO, 
but at tau ~2s or so, the tables are turned. I’m getting a good measure of my 
undisciplined 5680A as we speak to get a good control, but it’s difficult, as 
I’m testing it against a Thunderbolt, and I think I’m seeing its “hump” 
(http://www.leapsecond.com/pages/gpsdo/) from 10s to 300s coming through. In 
any event, I’m getting awfully close to the limits of my 53220a. I may go down 
the road of trying to make a mash-up as you suggest, but I’m going to start by 
seeing if I can give myself a choice between whether I want short term 
stability (OCXO) or medium term (Rubidium) for my reference.


> On Apr 20, 2016, at 1:57 PM, Attila Kinali  wrote:
> 
> On Wed, 20 Apr 2016 07:17:58 -0700
> Nick Sayer via time-nuts  wrote:
> 
>> I spent some time yesterday mashing together my FE-5680A "breakout" board 
>> with my GPSDO to make a GPS discipline board for it. Before I send the board 
>> off to OSHPark, I'd like to open the design to criticism (and I mean that in 
>> its neutral sense) here first.
> 
> Looking at your schematics, I would replace the input squarer (IC4)
> by something different than a schmitt-trigger with an input bias
> voltage. For one, schmitt-triggers are more noisy than normal buffers
> for an other, the bias voltage will result in a slightly skewed duty
> cycle. If you want to use a gate, then the canoncical way would be to
> use an inverter with an input capacitor like you did, but let it self-bias
> itself by using a 100k-1M resistor from its output to its input.
> Important: don't use a buffer, as this will only work with an inverter.
> But I'd rather use a different squaring circuit, if you want to use
> the input directly for the output. There are many discussions on
> squaring circuits in the archives. Probably the most simple, yet sofisticated
> is the one you can find in the TADD-2.
> 
> 
> But:
> As you can see on http://www.ke5fx.com/rb.htm the phase noise of the
> FE 5680's is horrible at best, hence I wouldn't use it as source for
> anything directly. Additionally, the tuning word you write through
> the RS-232 is stored in an EEPROM inside the FE-5860 (unless i mix
> it up with another Rb). Writing this tuning word often will wear out
> the EEPROM pretty quickly. Hence you should not do this too often.
> 
> What I would do instead is, use your current GPSDO design, with OCXO
> and all, but add something with which you can measure the phase/frequency
> of an external 10MHz reference. One way would be to use a digital DMTD[1,2].
> Another would be to sample the reference using an ADC and build DMTD in
> the digital domain. For this you wouldn't need a high sampling rate, a
> couple of kHz should be enough, as long as the analog bandwidth of the
> ADC is high enough (>10MHz, better >20MHz). What you need is some PLL
> though, as you need to create a frequency that is not an integer divisible
> of 10MHz, as the ADC clock is used to downmix the reference frequency.
> 
> Eg:
> If you can generate a 10001Hz ADC sampling clock from the OCXO,
> you will get a 1kHz beat frequency. You can "lock" to this using a
> digital PLL combined with an NCO (numerically controlled oscillator).
> Then use the steering word for the NCO as an input for the control
> loop of the OCXO, toghether with the corrections calculated from the
> GPS PPS.
> 
> The advantage of this is, that you get the low phase noise and good
> short term stability of the OCXO, but can use the Rb to get the nice
> mid-term stability (somewhere from 1 to 10s up) while getting the
> accuracy of a GPSDO, whithout ever the need of writing to the tuning
> word of the Rb. That keeps your Rb more stable (the internal conditions
> of the Rb do not change) and allows you to compensate for quite large
> frequency offsets for Rb refernces that are working outside the spec,
> but are otherwise fine.
> 
> One thing that you have to take care of is spurs, though. Because
> the ADC does some heavy down-mixing, or rather sub-sampling, this
> approach is quite sensitive to spurs. In order to not introduce some
> weird oscillations in the control loop due to spurs in the reference
> signal, you should use some narrow 10MHz filter at the input (at most
> half the sampling frequency wide). One way to achieve that is using a
> ceramic resonator which are available at 10MHz.
> 
>   Attila Kinali
> 
> PS: I'm pretty sure I am not the first one with this idea. But I have never
> seen anyone else mention it, much less implement it. Does anyone know why?
> 
> 
> [1] "Digital Dual Mixer Time Difference for Sub-Nanosecond Time
> 

Re: [time-nuts] RG6 or LMR400 for GPS Antenna (Symmetricom 58532A and T-bolt)

[Bob Camp]

Hi

RG-6 Quad Shield should be fine as long as it’s meeting the published specs. 
The advantage of LRM-400 is that you likely *know* where it came from and what 
the specs are. 

If you decide to split the antenna between GPSDO’s, a powered splitter is a 
really good idea. Each time you split another 2 ways, you loose 3 db. Get at 
least a 4 way splitter ….

Bob

> On Apr 20, 2016, at 4:41 PM, Ryan Stasel  wrote:
> 
> All, 
> 
> I’m going to be installing a “permanent” antenna at home, and will need a run 
> of about 100ft to get from my workstation, to the mast I’ll be mounting the 
> antenna on (Symmetricom 58532A). I’ve seen some indication that both the 
> antenna and the Trimble Thunderbolt won’t have any issues with running over 
> 75ohm cable, but thought I’d ask the “experts” whether I’d be better off with 
> some RG6 Quad-shield, or LMR400 (I’ve got a local source that doesn’t know 
> what LMR400 is, or what it’s worth)? 
> 
> Obviously I’d prefer to run and crimp RG6, but if I’d be better off with 
> LMR400, I’d rather run that now than go back into the crawlspace again. =)
> 
> Also, if it helps, I’ll probably have a Symmetricom/HP 58516A at/near the 
> T-bolt so I can experiment with other GPS(DO)s as well (especially one of the 
> JRMiller boards I bought and built (but never finished) ages ago). Which 
> brings the question, will the T-bolt provide the oomph needed to power that 
> splitter and the antenna over that length of cable? 
> 
> Thanks! 
> 
> -Ryan Stasel
> 
> 
> ___
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Re: [time-nuts] Adapting my GPSDO to the FE-5680A

[Bruce Griffiths]

There's the small matter of the high phase shift tempco of the narrow 10MHz 
bandpass filters Q~10,000 or so.These would need to either track very closely 
or be in an oven with very high temperature stability.The PN contribution of 
these analog filters may also be an issue.
 
Bruce

On Thursday, 21 April 2016 9:03 AM, Attila Kinali  wrote:
 

 On Wed, 20 Apr 2016 07:17:58 -0700
Nick Sayer via time-nuts  wrote:

> I spent some time yesterday mashing together my FE-5680A "breakout" board 
> with my GPSDO to make a GPS discipline board for it. Before I send the board 
> off to OSHPark, I'd like to open the design to criticism (and I mean that in 
> its neutral sense) here first.

Looking at your schematics, I would replace the input squarer (IC4)
by something different than a schmitt-trigger with an input bias
voltage. For one, schmitt-triggers are more noisy than normal buffers
for an other, the bias voltage will result in a slightly skewed duty
cycle. If you want to use a gate, then the canoncical way would be to
use an inverter with an input capacitor like you did, but let it self-bias
itself by using a 100k-1M resistor from its output to its input.
Important: don't use a buffer, as this will only work with an inverter.
But I'd rather use a different squaring circuit, if you want to use
the input directly for the output. There are many discussions on
squaring circuits in the archives. Probably the most simple, yet sofisticated
is the one you can find in the TADD-2.


But:
As you can see on http://www.ke5fx.com/rb.htm the phase noise of the
FE 5680's is horrible at best, hence I wouldn't use it as source for
anything directly. Additionally, the tuning word you write through
the RS-232 is stored in an EEPROM inside the FE-5860 (unless i mix
it up with another Rb). Writing this tuning word often will wear out
the EEPROM pretty quickly. Hence you should not do this too often.

What I would do instead is, use your current GPSDO design, with OCXO
and all, but add something with which you can measure the phase/frequency
of an external 10MHz reference. One way would be to use a digital DMTD[1,2]..
Another would be to sample the reference using an ADC and build DMTD in
the digital domain. For this you wouldn't need a high sampling rate, a
couple of kHz should be enough, as long as the analog bandwidth of the
ADC is high enough (>10MHz, better >20MHz). What you need is some PLL
though, as you need to create a frequency that is not an integer divisible
of 10MHz, as the ADC clock is used to downmix the reference frequency.

Eg:
If you can generate a 10001Hz ADC sampling clock from the OCXO,
you will get a 1kHz beat frequency. You can "lock" to this using a
digital PLL combined with an NCO (numerically controlled oscillator).
Then use the steering word for the NCO as an input for the control
loop of the OCXO, toghether with the corrections calculated from the
GPS PPS.

The advantage of this is, that you get the low phase noise and good
short term stability of the OCXO, but can use the Rb to get the nice
mid-term stability (somewhere from 1 to 10s up) while getting the
accuracy of a GPSDO, whithout ever the need of writing to the tuning
word of the Rb. That keeps your Rb more stable (the internal conditions
of the Rb do not change) and allows you to compensate for quite large
frequency offsets for Rb refernces that are working outside the spec,
but are otherwise fine.

One thing that you have to take care of is spurs, though. Because
the ADC does some heavy down-mixing, or rather sub-sampling, this
approach is quite sensitive to spurs. In order to not introduce some
weird oscillations in the control loop due to spurs in the reference
signal, you should use some narrow 10MHz filter at the input (at most
half the sampling frequency wide). One way to achieve that is using a
ceramic resonator which are available at 10MHz.

            Attila Kinali

PS: I'm pretty sure I am not the first one with this idea. But I have never
seen anyone else mention it, much less implement it. Does anyone know why?


[1] "Digital Dual Mixer Time Difference for Sub-Nanosecond Time
Synchronization in Ethernet", by Moreira, Alvares, Serrano, Darwezeh and
Wlostowski, 2010

[2] "Digital femtosecond time difference circuit for CERN's timing system",
by Moreira, Darwazeh, 2011
http://www.ee.ucl.ac.uk/lcs/previous/LCS2011/LCS1136.pdf

-- 
Reading can seriously damage your ignorance.
        -- unknown
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Re: [time-nuts] RG6 or LMR400 for GPS Antenna (Symmetricom 58532A and T-bolt)

[paul swed]

Ryan,
Several comments. LMR400 at 1500 Mhz is 5.1 db loss. RG 6 typically does
not seem to have a spec that I could see in this range. But will guess
9-10db. So at least 3 db more.
But that said RG6 has been used for Sat TV downlinks for years just fine
and I have used it for GPS just fine also. However I ran across a to good
to be true deal and did replace the link with LMR400 yes it made a
difference. Would I pay brand new price for LMR400 nope. My runs about 90'
all in.
Other consideration is ease of routing and terminating. RG6 is about as
easy as it gets. You can actually buy RG6 BNC connectors. I purchased a
number of crimp ones and they really work nicely.
Regards
Paul
WB8TSL

On Wed, Apr 20, 2016 at 4:41 PM, Ryan Stasel  wrote:

> All,
>
> I’m going to be installing a “permanent” antenna at home, and will need a
> run of about 100ft to get from my workstation, to the mast I’ll be mounting
> the antenna on (Symmetricom 58532A). I’ve seen some indication that both
> the antenna and the Trimble Thunderbolt won’t have any issues with running
> over 75ohm cable, but thought I’d ask the “experts” whether I’d be better
> off with some RG6 Quad-shield, or LMR400 (I’ve got a local source that
> doesn’t know what LMR400 is, or what it’s worth)?
>
> Obviously I’d prefer to run and crimp RG6, but if I’d be better off with
> LMR400, I’d rather run that now than go back into the crawlspace again. =)
>
> Also, if it helps, I’ll probably have a Symmetricom/HP 58516A at/near the
> T-bolt so I can experiment with other GPS(DO)s as well (especially one of
> the JRMiller boards I bought and built (but never finished) ages ago).
> Which brings the question, will the T-bolt provide the oomph needed to
> power that splitter and the antenna over that length of cable?
>
> Thanks!
>
> -Ryan Stasel
>
>
> ___
> 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.
>
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Re: [time-nuts] Adapting my GPSDO to the FE-5680A

[Attila Kinali]

On Wed, 20 Apr 2016 07:17:58 -0700
Nick Sayer via time-nuts  wrote:

> I spent some time yesterday mashing together my FE-5680A "breakout" board 
> with my GPSDO to make a GPS discipline board for it. Before I send the board 
> off to OSHPark, I'd like to open the design to criticism (and I mean that in 
> its neutral sense) here first.

Looking at your schematics, I would replace the input squarer (IC4)
by something different than a schmitt-trigger with an input bias
voltage. For one, schmitt-triggers are more noisy than normal buffers
for an other, the bias voltage will result in a slightly skewed duty
cycle. If you want to use a gate, then the canoncical way would be to
use an inverter with an input capacitor like you did, but let it self-bias
itself by using a 100k-1M resistor from its output to its input.
Important: don't use a buffer, as this will only work with an inverter.
But I'd rather use a different squaring circuit, if you want to use
the input directly for the output. There are many discussions on
squaring circuits in the archives. Probably the most simple, yet sofisticated
is the one you can find in the TADD-2.


But:
As you can see on http://www.ke5fx.com/rb.htm the phase noise of the
FE 5680's is horrible at best, hence I wouldn't use it as source for
anything directly. Additionally, the tuning word you write through
the RS-232 is stored in an EEPROM inside the FE-5860 (unless i mix
it up with another Rb). Writing this tuning word often will wear out
the EEPROM pretty quickly. Hence you should not do this too often.

What I would do instead is, use your current GPSDO design, with OCXO
and all, but add something with which you can measure the phase/frequency
of an external 10MHz reference. One way would be to use a digital DMTD[1,2].
Another would be to sample the reference using an ADC and build DMTD in
the digital domain. For this you wouldn't need a high sampling rate, a
couple of kHz should be enough, as long as the analog bandwidth of the
ADC is high enough (>10MHz, better >20MHz). What you need is some PLL
though, as you need to create a frequency that is not an integer divisible
of 10MHz, as the ADC clock is used to downmix the reference frequency.

Eg:
If you can generate a 10001Hz ADC sampling clock from the OCXO,
you will get a 1kHz beat frequency. You can "lock" to this using a
digital PLL combined with an NCO (numerically controlled oscillator).
Then use the steering word for the NCO as an input for the control
loop of the OCXO, toghether with the corrections calculated from the
GPS PPS.

The advantage of this is, that you get the low phase noise and good
short term stability of the OCXO, but can use the Rb to get the nice
mid-term stability (somewhere from 1 to 10s up) while getting the
accuracy of a GPSDO, whithout ever the need of writing to the tuning
word of the Rb. That keeps your Rb more stable (the internal conditions
of the Rb do not change) and allows you to compensate for quite large
frequency offsets for Rb refernces that are working outside the spec,
but are otherwise fine.

One thing that you have to take care of is spurs, though. Because
the ADC does some heavy down-mixing, or rather sub-sampling, this
approach is quite sensitive to spurs. In order to not introduce some
weird oscillations in the control loop due to spurs in the reference
signal, you should use some narrow 10MHz filter at the input (at most
half the sampling frequency wide). One way to achieve that is using a
ceramic resonator which are available at 10MHz.

Attila Kinali

PS: I'm pretty sure I am not the first one with this idea. But I have never
seen anyone else mention it, much less implement it. Does anyone know why?


[1] "Digital Dual Mixer Time Difference for Sub-Nanosecond Time
Synchronization in Ethernet", by Moreira, Alvares, Serrano, Darwezeh and
Wlostowski, 2010

[2] "Digital femtosecond time difference circuit for CERN's timing system",
by Moreira, Darwazeh, 2011
http://www.ee.ucl.ac.uk/lcs/previous/LCS2011/LCS1136.pdf

-- 
Reading can seriously damage your ignorance.
-- unknown
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[time-nuts] RG6 or LMR400 for GPS Antenna (Symmetricom 58532A and T-bolt)

[Ryan Stasel]

All, 

I’m going to be installing a “permanent” antenna at home, and will need a run 
of about 100ft to get from my workstation, to the mast I’ll be mounting the 
antenna on (Symmetricom 58532A). I’ve seen some indication that both the 
antenna and the Trimble Thunderbolt won’t have any issues with running over 
75ohm cable, but thought I’d ask the “experts” whether I’d be better off with 
some RG6 Quad-shield, or LMR400 (I’ve got a local source that doesn’t know what 
LMR400 is, or what it’s worth)? 

Obviously I’d prefer to run and crimp RG6, but if I’d be better off with 
LMR400, I’d rather run that now than go back into the crawlspace again. =)

Also, if it helps, I’ll probably have a Symmetricom/HP 58516A at/near the 
T-bolt so I can experiment with other GPS(DO)s as well (especially one of the 
JRMiller boards I bought and built (but never finished) ages ago). Which brings 
the question, will the T-bolt provide the oomph needed to power that splitter 
and the antenna over that length of cable? 

Thanks! 

-Ryan Stasel


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[time-nuts] Adapting my GPSDO to the FE-5680A

[Nick Sayer via time-nuts]

I spent some time yesterday mashing together my FE-5680A "breakout" board with 
my GPSDO to make a GPS discipline board for it. Before I send the board off to 
OSHPark, I'd like to open the design to criticism (and I mean that in its 
neutral sense) here first.

https://cdn.hackaday.io/files/6872294011648/GPS%20Disciplined%20FE5680%20v1_0.pdf

or

https://hackaday.io/project/6872-gps-disciplined-xcxo

And skip down to the latest log entry for discussion. 

I've seen John M's page that talks about the ADEV of the 5680A - in particular 
that it's low tau ADEV doesn't (to my eye) appear to be a whole lot better (if 
at all - I'm currently getting 8E-12 @ 2s) than the OH300. But I've got one, 
and it's got nothing better to do, and it'd be interesting to see how much 
benefit is to be had by improving the mid-tau performance over the OH300.

I've seen here posts about folks modifying the 5680 as part of a GPSDO. I'm not 
interested in doing that as my aspirations are not quite so high.  I just want 
to see what happens when the 5680A can be made accurate (well, more, anyway) as 
well as stable. 

Sent from my iPhone
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Re: [time-nuts] Trimble SMT 360

[Björn]

Why would the receiver swap between two solutions. One measurement is typically 
used to compute the time delta between the glonass and gps time.

--
     Björn

 Originalmeddelande Från: Bob Camp 
 Datum:2016-04-20  05:26  (GMT+07:00) 
Till: Discussion of precise time and frequency measurement 
 Rubrik: Re: [time-nuts] Trimble SMT 360 

Hi

Actually there is one other possibility: 

If you have more than one “system” enabled *and* it’s doing “all in view” *and* 
it’s applying that 
to the timing *and* the population in view changes significantly … (whew !) 

As the solution pops between GPS and Glonass, you will get a time shift. Since 
it’s a “which one
is right?” sort of thing … Trimble probably does not want to get into the 
debate. They would love
to sell stuff to everybody.

Bob


> On Apr 19, 2016, at 3:32 PM, Logan Cummings  wrote:
> 
> Hi Michael, Bob,
> 
> I had been very curious about this myself - the new ICM SMT 360
> modules at first glance seem like a great deal - < $50 and 10MHz TCXO
> disciplining built right in.
> 
> I came across this paper which compares the older (GPS-only) ICM SMT
> to a LEA-6T - the Trimble fares poorly in their testing.  The graphs don't
> show an issue quite like yours Michael, so I'd be curious about the line of
> questioning Bob brings up, how many satellites are being used by the
> receiver - say in GPS-only mode?
> 
> http://www.imeko.org/publications/tc10-2013/IMEKO-TC10-2013-028.pdf
> 
>Does anyone else have comparative experience with the new SMT modules
> from Trimble? RES or ICM?
> 
> Thanks,
> -Logan
> 
> On Tue, Apr 19, 2016 at 4:01 AM, Bob Camp  wrote:
> 
>> Hi
>> 
>> The two plots shown appear to be identical. If they are actually two
>> different
>> runs, the problem repeats very closely.
>> 
>> If the GPS is not in position hold *and* the antenna is less than ideal -
>> That’s
>> the sort of thing you may see. Essentially it’s got two locations it
>> “thinks” are
>> correct. Another possibility is a position hold situation with a very low
>> satellite count.
>> As a single observed satellite goes in and out of multi path, the solution
>> goes all over the place.
>> Again, you need a challenged antenna for this to happen. Pretty much all
>> of this
>> would be apparent from the normal messages out of the part.
>> 
>> Bob
>> 
>> 
>> 
>>> On Apr 18, 2016, at 10:13 PM, Michael Wouters 
>> wrote:
>>> 
>>> Does anyone have  experience with the Trimble SMT 360 ?
>>> 
>>> I bought some of these four or five months after they were released.
>> During
>>> testing, the 1 pps output evidenced a problem, as shown in the attached
>>> plot (the 1 pps is being measured against a Cs  beam standard), which is
>>> not sawtooth-corrected. While there are longish periods of nominal
>>> operation, the receiver seems to hop between two solutions.  This
>> behaviour
>>> is well out of specification.
>>> 
>>> When I contacted Trimble support, they said that the firmware in the
>>> receivers was very early, and replaced the receivers. However, the
>> problem
>>> was still evident with the new firmware. Trimble did not respond to
>> further
>>> emails.
>>> 
>>> I tried many things to isolate the problem, including restricting the
>>> receiver to GPS-only but I was unable to make an improvement.
>>> 
>>> I would like to know if anyone else is operating an SMT 360 and if they
>>> have seen any similar behaviour.
>>> 
>>> Cheers[image: Inline image 2]
>>> Michael[image: Inline image 1]
>>> ___
>>> time-nuts mailing list -- time-nuts@febo.com
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>>> and follow the instructions there.
>> 
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