Re: [time-nuts] I've been thinking about a GPS receiver experiment

[Ole Petter Ronningen]

I did log the #TIME message for several weeks on an OEMV-3 a while back.
The results were a bit suspicious, so I checked with Novatel support -
turns out the PPS on the OEMV (and I presume that also holds for OEM4) is
derived from L1 only - and the jitter is nothing to brag about. So for
disciplining with PPS, something like a UBlox would be better as far as I
can tell.

The other option is to log the #RANGE-message from the Novatel, convert to
RINEX and solve with PPP, and use the output of that to adjust the
rubidium. The added benefit is that you'll have an excellent log of what
your reference is doing if you get odd results in some measurements.

Ole

On Wed, Oct 25, 2017 at 12:56 AM, Magnus Danielson <
mag...@rubidium.dyndns.org> wrote:

> Skip,
>
> I would rather use the rich Novatel reports and read out the time error
> and use that as your phase detector, then the normal PI-loop stuff with an
> optional low-pass to add and then use that to steer the rubidium.
>
> It's one of those, when I get time, projects.
>
> Cheers,
> Magnus
>
>
> On 10/25/2017 12:17 AM, Skip Withrow wrote:
>
>> Hello time-nuts,
>>
>> I've been thinking about a GPS receiver experiment and just wondering
>> if there are any opinions or prior experience that might save me a lot
>> of time.
>>
>> What I have been thinking about doing is taking a GPS receiver
>> (Novatel OEM4-G2) that has provisions for an external clock (5 or 10
>> MHz) and driving it with a rubidium oscillator (that has 1pps
>> disciplining, (such as the X72 v5.05 or SRS PRS-10).  The GPS even has
>> settings for OCXO/rubidium/cesium dynamics.
>>
>> Then, (and here is the unknown part) what if the GPS receiver 1pps is
>> used to discipline the rubidium?  This basically forms a feedback
>> loop, so could either hurt or help - depending.  Supposedly the better
>> oscillator would give a better GPS solution.  And the better solution
>> (1pps) should provide a better oscillator frequency.
>>
>> We know that GPS receivers using asynchronous clocks have 1pps errors
>> and hanging bridges (OEM4 is spec'd at 20ns rms), If the oscillator is
>> on 10MHz and disciplined will the 1pps error be reduced such as the
>> Thunderbolt?
>>
>> Comments appreciated.
>>
>> Regards,
>> Skip Withrow
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[time-nuts] Datum/Symmetricom Tymserve TS2100 GPS NTP Server Questions

[Raoul Duke via time-nuts]

> The SV6's are all well past their rollover date.  
>
>A common problem with the SV6 (and the Motorola 6 and 8 channel receivers)  is 
>the TCXO has drifted out of range.  Some have an adjustment cap that can be 
>tweaked.

I'll look into that.  For the moment it appears that separating the TS2100 from 
other equipment, reducing internal temperatures, seems to be working.

The web page of the other TS2100, with the SV6, reports that it is in "Timecode 
Decoding Mode" and "Freewheeling".  Telnetting in: "timing / gps / health" 
returns "GPS Engine Busy", "timing / gps / health" returns "GPS Engine Busy:2", 
"signal" returns "*** err *** handshake timeout", "satellites" returns "*** err 
*** gps error" and "gpsversion" returns "GPS Engine Busy".  Does this imply 
that the SV6 is dead or just lost?  Are there any other diagnostics I should 
try?

The working (for now) TS2100 "gpsversion" returns "Nav 5.10 6/3/97 Sig 1.18 
6/2/97" - does that identify its GPS receiver as an SV6 too?

Aside from that, the older TS2100 is definitely working, with correct time, and 
has been for months.  And we are now two years past Trimble's 1024 week bug, so 
I'm not really sure what you mean.  I take it that I shouldn't bother to 
upgrade to the 4.1 firmware?  And there is no schematic information available 
for replacing the XO for an OCXO?
Thanks

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Re: [time-nuts] inexpensive, black box, GPS or NTP based TTL time capture?

[jimlux]

On 10/24/17 5:04 PM, Nick Sayer via time-nuts wrote:

FWIW, I’ve documented the whole R-Pi GPS NTP thing at 
https://hackaday.io/project/15137

As a disclaimer I will also say that I’m not even remotely the first. But 
what’s kind of nice is that I have a R-Pi desk clock display board that plays 
really well with a bolt-on GPS cap. In fact, I’ve got two of them in the NTP 
pool right now.

Sent from my iPhone





I've been connecting a Parallax NEO-7M to a beaglebone green..
GPS messages through the UART are easy.

pps less so.. I'm sure it's a matter of correctly configuring and 
thrashing through the GPIO assignments with the capemgr - which 
interestingly has had two substantial versions - most of the online 
tutorials and material refer to the older one.



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Re: [time-nuts] inexpensive, black box, GPS or NTP based TTL time capture?

[Nick Sayer via time-nuts]

FWIW, I’ve documented the whole R-Pi GPS NTP thing at 
https://hackaday.io/project/15137

As a disclaimer I will also say that I’m not even remotely the first. But 
what’s kind of nice is that I have a R-Pi desk clock display board that plays 
really well with a bolt-on GPS cap. In fact, I’ve got two of them in the NTP 
pool right now.

Sent from my iPhone

> On Oct 21, 2017, at 7:50 AM, ROY PHILLIPS  wrote:
> 
> 
> Original message
> From : hmur...@megapathdsl.net
> Date : 21/10/2017 - 7:49 am (GMTDT)
> To : g...@rellim.com
> Cc : time-nuts@febo.com, hmur...@megapathdsl.net
> Subject : Re: [time-nuts] inexpensive, black box, GPS or NTP based TTL time 
> capture?
> 
 For under a $100 you could get a Raspberry Pi, a GPS HAT, and
 connect your input to a GPIO pin.  Configure ntpd to log the real
 PPS and the input as another 'PPS'.
> 
>>> Is there an option to log all individual PPS events?
> 
>>   # ppswatch /dev/pps0
> 
> That's a way to log stuff, but I don't think it comes under "Configure ntpd".
> 
> I remember some option to log lots of stuff, but I don't remember the 
> details.  It could have been in a driver.  I couldn't find it in the man page 
> for the PPS driver.
> 
> [amazon]
>> Looks like $96 to me.  You can save some if you buy in bulk,
> 
> You can save $7 if you get the starter package that has only Pi, SD card, 
> power, and case.  (Many starter packages include stuff you probably don't 
> need and that raises the price.  But maybe one has a HDMI adapter.  I didn't 
> look.)
> 
> Beware of using normal USB cables and/or normal USB power supplies.  The Pi 
> is not happy with low voltage.  The drop in a USB cable can be significant.  
> The setups intended for use with Pis normally have 5.1 or 5.25 volts and 
> heavier gage wire in the cable.
> 
> 
> [display, kbd, mouse...]
>> Yeah, just for setup.  Shall we include the price of the desk it sits and
>> the building it is in?
> 
> I'm willing to assume somebody has a table and a roof.
> 
> The display and such are not a problem if you have a PC you can borrow them 
> from.  (You probably need a HDMI adapter.)  But that doesn't work if all you 
> have is a laptop or smart phone.
> 
> I think most of my friends have PCs but I wouldn't be surprised if some of 
> them had a laptop and no PC.
> 
> If your PC is old enough, the keyboard and mouse may be PS2 rather than USB.
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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Re: [time-nuts] I've been thinking about a GPS receiver experiment

[Bob kb8tq]

Hi

The “best” approach would be to use a receiver that reports what’s going on to 
some pretty
good resolution (say picoseconds). You also measure the pps offset (say to 
picoseconds). 
Then you feed *both* numbers into a software loop. 

Since you are after a loop with a “many days” sort of response, you have *lots* 
of time to do the 
math. Updates every minute are probably overkill. Since the math can take a 
long time, the CPU
requirements aren’t very crazy. Equally, you can use a PC and get the job done. 
OS overhead 
likely isn’t going to be a big deal. 

You can separate out the math and run it at a pretty high level. Tweaking this 
or that would all 
be done in a high level language. No need for going crazy with assembler The 
loop is likely to 
be a “step and wait” sort of thing. There will be a bit of tweaking. Doing that 
in something easy
to use *is* an advantage. Having it buried in some mystery firmware written by 
who knows who
is not a good thing in this case. 

Bob


> On Oct 24, 2017, at 7:09 PM, Dana Whitlow  wrote:
> 
> Hello Skip,
> 
> I have a theory, but it will be interesting to see what others say.
> Assuming that the
> 1 PPS error to which you refer is the so-called "sawtooth" error, I've come
> to suspect
> that the rate at which the individual PPS pulses walk across the sawtooth
> is related to,
> and likely proportional to, the error of the internal (or in this case, the
> external) clock
> oscillator.  If I'm right about its being proportional, then it seems to me
> that having
> the GPS's clock oscillator right on would freeze the PPS error at some
> fixed value,
> not necessarily zero.  If true, you'd experience a constant bias error to
> the timing of
> the PPS pulses.
> 
> Now you would seem to be in the perfect position to refute or verify my
> thinking,
> provided you have the means to vary an external clock's frequency in a
> controlled
> way, by watching how the PPS error behavior changes as a function of the
> clock
> frequency.
> 
> If you manage to try the experiment, I'd greatly appreciate hearing the
> outcome.
> 
> DanaK8YUM
> 
> 
> On Tue, Oct 24, 2017 at 5:17 PM, Skip Withrow 
> wrote:
> 
>> Hello time-nuts,
>> 
>> I've been thinking about a GPS receiver experiment and just wondering
>> if there are any opinions or prior experience that might save me a lot
>> of time.
>> 
>> What I have been thinking about doing is taking a GPS receiver
>> (Novatel OEM4-G2) that has provisions for an external clock (5 or 10
>> MHz) and driving it with a rubidium oscillator (that has 1pps
>> disciplining, (such as the X72 v5.05 or SRS PRS-10).  The GPS even has
>> settings for OCXO/rubidium/cesium dynamics.
>> 
>> Then, (and here is the unknown part) what if the GPS receiver 1pps is
>> used to discipline the rubidium?  This basically forms a feedback
>> loop, so could either hurt or help - depending.  Supposedly the better
>> oscillator would give a better GPS solution.  And the better solution
>> (1pps) should provide a better oscillator frequency.
>> 
>> We know that GPS receivers using asynchronous clocks have 1pps errors
>> and hanging bridges (OEM4 is spec'd at 20ns rms), If the oscillator is
>> on 10MHz and disciplined will the 1pps error be reduced such as the
>> Thunderbolt?
>> 
>> Comments appreciated.
>> 
>> Regards,
>> Skip Withrow
>> ___
>> time-nuts mailing list -- time-nuts@febo.com
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>> mailman/listinfo/time-nuts
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Re: [time-nuts] I've been thinking about a GPS receiver experiment

[Dana Whitlow]

Hello Skip,

I have a theory, but it will be interesting to see what others say.
Assuming that the
1 PPS error to which you refer is the so-called "sawtooth" error, I've come
to suspect
that the rate at which the individual PPS pulses walk across the sawtooth
is related to,
and likely proportional to, the error of the internal (or in this case, the
external) clock
oscillator.  If I'm right about its being proportional, then it seems to me
that having
the GPS's clock oscillator right on would freeze the PPS error at some
fixed value,
not necessarily zero.  If true, you'd experience a constant bias error to
the timing of
the PPS pulses.

Now you would seem to be in the perfect position to refute or verify my
thinking,
provided you have the means to vary an external clock's frequency in a
controlled
way, by watching how the PPS error behavior changes as a function of the
clock
frequency.

If you manage to try the experiment, I'd greatly appreciate hearing the
outcome.

DanaK8YUM


On Tue, Oct 24, 2017 at 5:17 PM, Skip Withrow 
wrote:

> Hello time-nuts,
>
> I've been thinking about a GPS receiver experiment and just wondering
> if there are any opinions or prior experience that might save me a lot
> of time.
>
> What I have been thinking about doing is taking a GPS receiver
> (Novatel OEM4-G2) that has provisions for an external clock (5 or 10
> MHz) and driving it with a rubidium oscillator (that has 1pps
> disciplining, (such as the X72 v5.05 or SRS PRS-10).  The GPS even has
> settings for OCXO/rubidium/cesium dynamics.
>
> Then, (and here is the unknown part) what if the GPS receiver 1pps is
> used to discipline the rubidium?  This basically forms a feedback
> loop, so could either hurt or help - depending.  Supposedly the better
> oscillator would give a better GPS solution.  And the better solution
> (1pps) should provide a better oscillator frequency.
>
> We know that GPS receivers using asynchronous clocks have 1pps errors
> and hanging bridges (OEM4 is spec'd at 20ns rms), If the oscillator is
> on 10MHz and disciplined will the 1pps error be reduced such as the
> Thunderbolt?
>
> Comments appreciated.
>
> Regards,
> Skip Withrow
> ___
> time-nuts mailing list -- time-nuts@febo.com
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> mailman/listinfo/time-nuts
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Re: [time-nuts] Spice simulation of PSRR and phase noise

[jimlux]

On 10/24/17 11:54 AM, Bob kb8tq wrote:

Hi

If you have the money, almost anything can be (and has been) done. It’s rare to 
find a
real world application where this kind of thing is considered cost effective. 
Fancy
radar systems are about the only thing that comes to mind.  Radar of
this sort is always high cost / low volume.



Deep Space Network stations or other applications (VLBI) where the 
measurement uncertainty is like ADEV = 1E-12 in 1000 seconds. There's a 
whole analysis of the temperature effects on the fiber optic 
distribution components, for instance - and they're buried 2 meters down.


At "billions of dollars in 1960/1970" I think DSN fits in Bob's high 
cost/low volume bucket.





Bob


On Oct 24, 2017, at 2:10 PM, Hal Murray  wrote:


aph...@comcast.net said:

  My applications were broadband. If I remember correctly,  aggressive
bandwidth limiting can cause phase shift problems due to  temperature
changes unless one is careful in the design of the filter.


Does anybody ovenize amplifiers and filters to avoid that problem?


--
These are my opinions.  I hate spam.



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Re: [time-nuts] I've been thinking about a GPS receiver experiment

[Magnus Danielson]

Skip,

I would rather use the rich Novatel reports and read out the time error 
and use that as your phase detector, then the normal PI-loop stuff with 
an optional low-pass to add and then use that to steer the rubidium.


It's one of those, when I get time, projects.

Cheers,
Magnus

On 10/25/2017 12:17 AM, Skip Withrow wrote:

Hello time-nuts,

I've been thinking about a GPS receiver experiment and just wondering
if there are any opinions or prior experience that might save me a lot
of time.

What I have been thinking about doing is taking a GPS receiver
(Novatel OEM4-G2) that has provisions for an external clock (5 or 10
MHz) and driving it with a rubidium oscillator (that has 1pps
disciplining, (such as the X72 v5.05 or SRS PRS-10).  The GPS even has
settings for OCXO/rubidium/cesium dynamics.

Then, (and here is the unknown part) what if the GPS receiver 1pps is
used to discipline the rubidium?  This basically forms a feedback
loop, so could either hurt or help - depending.  Supposedly the better
oscillator would give a better GPS solution.  And the better solution
(1pps) should provide a better oscillator frequency.

We know that GPS receivers using asynchronous clocks have 1pps errors
and hanging bridges (OEM4 is spec'd at 20ns rms), If the oscillator is
on 10MHz and disciplined will the 1pps error be reduced such as the
Thunderbolt?

Comments appreciated.

Regards,
Skip Withrow
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[time-nuts] I've been thinking about a GPS receiver experiment

[Skip Withrow]

Hello time-nuts,

I've been thinking about a GPS receiver experiment and just wondering
if there are any opinions or prior experience that might save me a lot
of time.

What I have been thinking about doing is taking a GPS receiver
(Novatel OEM4-G2) that has provisions for an external clock (5 or 10
MHz) and driving it with a rubidium oscillator (that has 1pps
disciplining, (such as the X72 v5.05 or SRS PRS-10).  The GPS even has
settings for OCXO/rubidium/cesium dynamics.

Then, (and here is the unknown part) what if the GPS receiver 1pps is
used to discipline the rubidium?  This basically forms a feedback
loop, so could either hurt or help - depending.  Supposedly the better
oscillator would give a better GPS solution.  And the better solution
(1pps) should provide a better oscillator frequency.

We know that GPS receivers using asynchronous clocks have 1pps errors
and hanging bridges (OEM4 is spec'd at 20ns rms), If the oscillator is
on 10MHz and disciplined will the 1pps error be reduced such as the
Thunderbolt?

Comments appreciated.

Regards,
Skip Withrow
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Re: [time-nuts] Spice simulation of PSRR and phase noise

[Bob kb8tq]

Hi

If you have the money, almost anything can be (and has been) done. It’s rare to 
find a 
real world application where this kind of thing is considered cost effective. 
Fancy 
radar systems are about the only thing that comes to mind.  Radar of 
this sort is always high cost / low volume. 

Bob

> On Oct 24, 2017, at 2:10 PM, Hal Murray  wrote:
> 
> 
> aph...@comcast.net said:
>>  My applications were broadband. If I remember correctly,  aggressive
>> bandwidth limiting can cause phase shift problems due to  temperature
>> changes unless one is careful in the design of the filter. 
> 
> Does anybody ovenize amplifiers and filters to avoid that problem?
> 
> 
> -- 
> These are my opinions.  I hate spam.
> 
> 
> 
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Re: [time-nuts] Spice simulation of PSRR and phase noise

[Richard (Rick) Karlquist]

On 10/24/2017 11:10 AM, Hal Murray wrote:


aph...@comcast.net said:

   My applications were broadband. If I remember correctly,  aggressive
bandwidth limiting can cause phase shift problems due to  temperature
changes unless one is careful in the design of the filter.


Does anybody ovenize amplifiers and filters to avoid that problem?



This problem came up in the design of the 5071A.
I elected to avoid narrowband filters by using
some tricks described in my FCS paper of about
25 years ago.  I didn't find it necessary to ovenize
the output section.

By contrast, the 5061 had numerous narrow band filters
that were problematical.

Rick N6RK
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Re: [time-nuts] Spice simulation of PSRR and phase noise

[Hal Murray]

aph...@comcast.net said:
>   My applications were broadband. If I remember correctly,  aggressive
> bandwidth limiting can cause phase shift problems due to  temperature
> changes unless one is careful in the design of the filter. 

Does anybody ovenize amplifiers and filters to avoid that problem?


-- 
These are my opinions.  I hate spam.



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Re: [time-nuts] Spice simulation of PSRR and phase noise

[Bob Martin]

I never had much luck with current feedback amplifiers such as the 
LMH6702.  Their input current noise (at the time) was too high for 
my needs and their output peaks at higher frequencies if the 
feedback resistors aren't optimal for the part.


 I had the best results with voltage feedback op amps like the 
MAX4104/MAX3404 when I needed gain on the input stage and the 
LMH6609 when I needed a buffer.


 My applications were broadband. If I remember correctly, 
aggressive bandwidth limiting can cause phase shift problems due to 
temperature changes unless one is careful in the design of the filter.


 I've successfully put as many as four op amps in parallel in an 
input stage to reduce phase noise.



Bob M (another bob)

On 10/24/2017 6:24 AM, Bob kb8tq wrote:

Hi

One would guess that they put them in parallel to get more drive. If that’s 
correct,
details of the loading are going to get into the simulation pretty quickly.

In a lot of cases, these amplifiers were designed against a specific need. If 
you have
a signal source that is in the -180 dbc / Hz range, they are unlikely do 
perform well.
In many cases a floor in the -140 dbc / Hz range was considered “good enough”.
If you are simply driving common test gear, it probably *is* good enough. If the
application was video rather than a standard the specs could have been very 
different.

In the case of an amp with a LMH6702, you are not going to get super  close in
phase noise. The device is *very* noisy under 1 MHz. It also starts to increase 
distortion
by 10 MHz so you will see up conversion. It probably did quite well against the 
intended
design spec.

=

If you need a system that will distribute one frequency today and a totally 
different
frequency tomorrow, broadband makes sense. For the more common task of
something like “only 10 MHz”, it does not make much sense at all. Gain other
  frequencies is just going to spread around noise from this or that source
of crud. Driving filters with op amps can be problematic. It often is easier to 
go another
way.

Bob


On Oct 24, 2017, at 6:09 AM, Anders Wallin  wrote:

FWIW I recently took a peek inside a commercial distribution-amplifier and
it seems to use two LMH6702 op-amps in parallel.
There are two of these dual-LMH6702 stages with a 1:2 splitter after the
first, and then a 1:4 splitter after the second stage. 8 outputs in total,
with an additional op-amp driving each output.
A simulation that shows the difference in PN between a single LMH6702 and
the dual-op-amp idea would be nice.
For far-out (>100Hz from carrier?) PN only SNR might matter, so a SPICE
noise-simulation giving noise PSD at relevant (5-10MHz) frequencies might
give something?

Anders
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[time-nuts] Fwd: Distribution divider/amplifier for 10MHz GPSDO

[Mattia Rizzi]

Hi,

> Is it safe to have RG174 coming out of the
GPSDO, tapping into it with a BNC T-junction that plugs into the back of
each device that needs the 10mhz input, and then terminating the strand
with a 50 ohm terminator?

Besides the usual signal integrity issues, remember to provide a solid
earth connection between instruments.
Depending on the scenario, failure to do so can result in worse performance
than mismatched termination.

cheers,
Mattia

-- Forwarded message --
From: Jeremy Elson 
Date: 2017-10-23 19:49 GMT+02:00
Subject: Re: [time-nuts] Distribution divider/amplifier for 10MHz GPSDO
To: Discussion of precise time and frequency measurement 


I was about to ask a related question of the list: when do you need a
distribution amplifier, and when is it sufficient to just have a single
(linear) run of coax?

I have a GPSDO (Nick Sayer's device) that I want to use to feed a few other
pieces of equipment in my lab (an HP5335A, John Ackermann's beautiful TICC,
and a Rigol signal generator). Is it safe to have RG174 coming out of the
GPSDO, tapping into it with a BNC T-junction that plugs into the back of
each device that needs the 10mhz input, and then terminating the strand
with a 50 ohm terminator? (In other words, the way thinnet Ethernet was
wired back in the day.) As long as the signal goes in a straight line, not
a "Y" (i.e. no cables attached to the t-junction taps, just a direct input
into a high-z input) it seems like it should work. Do I need a distribution
amplifier? Or is that, say, if the signal needs to split off in multiple
directions and you don't want to fill your lab with a space-filling curve
of coax?

-Jeremy

On Mon, Oct 23, 2017 at 10:26 AM, Bob kb8tq  wrote:

> Hi
>
> The correct answer to any real question like this is “that depends”.
>
> For anything that I normally run as test gear, noise outside a very narrow
> bandwidth really
> does not matter much. The test gear *assumes* (by design) that the
> reference signal going
> into the “ref in” jack is not very clean. It does various tricks with
> filters and PLL’s to “scrub”
> the input.
>
> If we are talking about the reference into one side of a phase noise test
> set, then
> the situation is a bit different. The test set is simply going to tell me
> what the combined
> noise is on the two inputs. If one is significantly more noisy than the
> other, that’s pretty
> much all I will see. In this case, my answer is “don’t use a distributed
> signal”. Use a
> stand alone source as your reference and isolate it from the rest of the
> world.
>
> In any case, making a super duper distribution gizmo and feeding it with a
> noisy signal
> is not going to make the signal any better. Most GPSDO’s have relatively
> noisy outputs.
> Some are better than others. None that I have seen on the surplus market
> are what
> I would call quiet at the output jack of the GPSDO. They either have an
> ocean of spurs
> or a lot of phase noise. Some have both ….
>
> Any time you boost a bunch of signals up to high levels, you create “crud”
> running around your
> lab / shack. One of the most basic questions should always be “do I really
> need this signal?”. Next
> should be “how can I have a shorter run?”.  I have many pieces of gear
> that are rarely used.
> They use odd references. When I need to use them I rig a reference. That
> gets shut down
> once the gear goes back to storage. …. no more birdies every 100 KHz …. No
> need for
> tripple shielded coax ….
>
> Simple answer:
>
> Square up the 10 MHz (or whatever) by matching it into a 5.5 V powered
> high speed CMOS
> gate. The NC7SZ series is one of many families you can use. A NC7SZ125 is
> not a bad gate
> to pick. Distribute the square wave to however many output amps as you
> need. Each one
> is another of the same gates with the output matched via a 50 ohm to 50
> ohm lowpass Tee network
> with a low Q ( < 2). Likely pad down the output a bit to keep it at a
> rational level.  Build up however
> many you need for however many frequencies you require. Very normal linear
> regulator chips
> are fine for the power. Careful bypassing and solid ground planes are
> always a good idea.
> Parts cost wise, postage is likely to cost you more than the components.
> There are …. errr…
> many thousands …. of multi output amps of this basic  design out there ….
> they seem to
> work pretty well.
>
> Yes, there are *lots* of possible twists and turns to this. I’m only
> guessing about the gear you
> are trying to run and what you are trying to do with it.
>
> Bob
>
>
>
>
>
> > On Oct 23, 2017, at 12:45 PM, Tom Van Baak  wrote:
> >
> > List -- Don is having email trouble, but here's his posting:
> >
> > --
> >
> > From: donaldbcol...@gmail.com
> > Date: Tue, Oct 24, 2017 at 1:38 AM
> > Subject:   Distribution divider/amplifier for 10MHz GPSDO
> >
> > Hello group. I`m intending to distribute, via 50 Ohm coax, 

Re: [time-nuts] Spice simulation of PSRR and phase noise

[Bob kb8tq]

Hi

One would guess that they put them in parallel to get more drive. If that’s 
correct,
details of the loading are going to get into the simulation pretty quickly. 

In a lot of cases, these amplifiers were designed against a specific need. If 
you have
a signal source that is in the -180 dbc / Hz range, they are unlikely do 
perform well. 
In many cases a floor in the -140 dbc / Hz range was considered “good enough”. 
If you are simply driving common test gear, it probably *is* good enough. If 
the 
application was video rather than a standard the specs could have been very 
different. 

In the case of an amp with a LMH6702, you are not going to get super  close in 
phase noise. The device is *very* noisy under 1 MHz. It also starts to increase 
distortion
by 10 MHz so you will see up conversion. It probably did quite well against the 
intended
design spec. 

=

If you need a system that will distribute one frequency today and a totally 
different
frequency tomorrow, broadband makes sense. For the more common task of 
something like “only 10 MHz”, it does not make much sense at all. Gain other 
 frequencies is just going to spread around noise from this or that source
of crud. Driving filters with op amps can be problematic. It often is easier to 
go another
way. 

Bob

> On Oct 24, 2017, at 6:09 AM, Anders Wallin  
> wrote:
> 
> FWIW I recently took a peek inside a commercial distribution-amplifier and
> it seems to use two LMH6702 op-amps in parallel.
> There are two of these dual-LMH6702 stages with a 1:2 splitter after the
> first, and then a 1:4 splitter after the second stage. 8 outputs in total,
> with an additional op-amp driving each output.
> A simulation that shows the difference in PN between a single LMH6702 and
> the dual-op-amp idea would be nice.
> For far-out (>100Hz from carrier?) PN only SNR might matter, so a SPICE
> noise-simulation giving noise PSD at relevant (5-10MHz) frequencies might
> give something?
> 
> Anders
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Re: [time-nuts] Spice simulation of PSRR and phase noise

[Anders Wallin]

FWIW I recently took a peek inside a commercial distribution-amplifier and
it seems to use two LMH6702 op-amps in parallel.
There are two of these dual-LMH6702 stages with a 1:2 splitter after the
first, and then a 1:4 splitter after the second stage. 8 outputs in total,
with an additional op-amp driving each output.
A simulation that shows the difference in PN between a single LMH6702 and
the dual-op-amp idea would be nice.
For far-out (>100Hz from carrier?) PN only SNR might matter, so a SPICE
noise-simulation giving noise PSD at relevant (5-10MHz) frequencies might
give something?

Anders
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