Re: [time-nuts] TAPR TICC boxed

[Bruce Griffiths]

For even more fun you could try to detect the PTFE phase change  at around 20C 
using a cable with PTFE dielectric.

A pulse source with somewhat more pulse to pulse jitter may be more useful in 
that averaging will occur over a wider range of fine interpolator codes.

Bruce

> 
> On 03 April 2017 at 05:34 Mark Sims  wrote:
> 
> I implemented the channel offset compensation feature specifically to 
> make measuring cable delays more accurate. I wanted to measure my TDR 
> calibration cable and another very precision delay line. I used Heather to 
> null out the channel/connector delays and then replaced one of the "T" cables 
> with the TDR cable.
> 
> My test setup / TICC was coming up with a -306 ps channel offset error. 
> The test signal was the 1PPS output of a FTS4060 cesium. Connecting / 
> reconnecting one of the test setup cables and re-doing the offset test (I was 
> averaging for 1800 seconds) could produce compensation values that varied 
> from -300 ps to -325 ps. Just de-doing the offset test without messing with 
> the cables produced values around -300 to -310 ps.
> 
> BNC connectors aren't the best for precision timing. I need to re-run the 
> test with SMA cables / T adapter and the precision HP connector torque wrench 
> and see what that looks like. It would also be fun to lay a coax outdoors and 
> see how the delay changes over a day as it heats/cools.
> 
> 
> 
> > > 
> > Some “cables” have very long delay numbers.
> > 
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[time-nuts] TAPR TICC boxed

[Mark Sims]

The autotune cable delay nulling feature works by putting the TICC into debug 
mode which outputs time stamps (and other info) of both channels.   Since each 
channel is being fed by the same signal, the stamps of each channel should be 
the same.  Heather calculates the average chA-chB difference over a period of 
time and uses that difference to set the chA "fudge factor" which the TICC 
firmware subtracts from the chA readings.  This nulls the relative offset 
between the two channels, but does not (and cannot) determine the absolute 
delay offset of each channel.


> Its usually not possible to uniquely assign individual channel delays in this 
> way, however swapping cables allows the cable delay mismatch to be eliminated 
> from the measurement of the differential delay between channels.  Eliminating 
> the effect of cable delay mismatch can be useful when adjusting narrowband 
> quadrature splitters ect.

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[time-nuts] TAPR TICC boxed

[Mark Sims]

I implemented the channel offset compensation feature specifically to make 
measuring cable delays more accurate.  I wanted to measure my TDR calibration 
cable and another very precision delay line.  I used Heather to null out the 
channel/connector delays and then replaced one of the "T" cables with the TDR 
cable.  

My test setup / TICC was coming up with a -306 ps channel offset error.   The 
test signal was the 1PPS output of a FTS4060 cesium.   Connecting / 
reconnecting one of the test setup cables and re-doing the offset test (I was 
averaging for 1800 seconds) could produce compensation values that varied from 
-300 ps to -325 ps.   Just de-doing the offset test without messing with the 
cables produced values around -300 to -310 ps.   

BNC connectors aren't the best for precision timing.  I need to re-run the test 
with SMA cables / T adapter and the precision HP connector torque wrench and 
see what that looks like.  It would also be fun to lay a coax outdoors  and see 
how the delay changes over a day as it heats/cools.



> Some “cables” have very long delay numbers.
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Re: [time-nuts] TAPR TICC boxed (input protection)

[Charles Steinmetz]

The FJH1100 is specified for reverse leakage of 10pA at 15v (which is 
also the absolute maximum working voltage), and 3pA reverse leakage at 
5v.  Junction capacitance is 2pF.  They cost $8.90 each at Mouser.


The B-C junction of an MPSH10 or MMBTH10 (SMT version) has only half as 
much reverse leakage current (5pA) at a higher reverse voltage (20v).  I 
just measured a few MPSH10s at 5v, and they showed less than 1pA reverse 
leakage. The maximum working voltage is 30v and junction capacitance is 
0.7pF.  Switching times are 5-10x faster than the FJH1100.  MMBTH10s 
cost $0.22 each at Mouser.  MMBT5179s (SMT version of 2N5179) are very 
similar and cost $0.26 each at Mouser.


I have used the B-C junctions of BJTs and the gate junctions of JFETS as 
low-leakage diodes for many, many years, for exactly these reasons 
(better performance than "ultra low leakage" signal diodes and *much* 
lower cost).


Best regards,

Charles


On 3/31/2017 9:39 PM, Alex Pummer wrote:

FJH1100
Ultra Low Leakage Diode

Alex


On 3/31/2017 6:00 PM, Charles Steinmetz wrote:

Mark wrote:


I thought about using the clamp diodes as protection but was a bit
worried about power supply noise leaking through the diodes and
adding some jitter to the input signals...


It is a definite worry even with a low-noise, 50 ohm input, and a
potential disaster with a 1Mohm input.  Common signal diodes (1N4148,
1N914, 1N916, 1N4448, etc.) are specified for 5-10nA of reverse
current.  Even a low-leakage signal diode (e.g., 1N3595) typically has
several hundred pA of leakage.  Note that the concern isn't just power
supply noise -- the leakage current itself is quite noisy.

For low-picoamp diodes at a decent price, I use either (1) the B-C
diode of a small-signal BJT, or (2) the gate diode of a small-geometry
JFET. A 2N5550 makes a good high-voltage, low-leakage diode with
leakage current of ~30pA.  Small signal HF transistors like the MPSH10
and 2N5179 (and their SMD and PN variants) are good for ~5pA, while
the gate diode of a PN4417A JFET (or SMD variant) has reverse leakage
current of ~1pA (achieving this in practice requires a very clean
board and good layout).

I posted some actual leakage test results to Didier's site, which can
be downloaded at
.
 This document shows the connections I used to obtain the data.


The TICC doesn't have the resolution for it to matter or justify a
HP5370 or better quality front end. I'll probably go with a fast
comparator to implement the variable threshold input.


Properly applied, a fast comparator will have lower jitter than the
rest of the errors, and is an excellent choice.  Bruce suggested the
LTC6752, which is a great part if you need high toggle speeds (100s of
MHz) or ultra-fast edges.  But you don't need high toggle rates and
may not need ultra-fast edges. Repeatability and stability are more
important than raw speed in this application.  The LT1719, LT1720, or
TLV3501 may work just as well for your purpose, and they are
significantly less fussy to apply.

Note that the LTC6752 series is an improved replacement for the
ADCMP60x series, which itself is an improved replacement for the
MAX999.  Of these three, the LTC6752 is the clear winner in my tests.
If you do choose it (or similar), make sure you look at the
transitions with something that will honestly show you any chatter at
frequencies up to at least several GHz.  It only takes a little
transition chatter to knock the potential timing resolution of the
ultra-fast comparator way down.  Do make sure to test it with the
slowest input edges you need it to handle.

Best regards,

Charles


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[time-nuts] CXR Larus STS 54500 Synchronus Timing System

[Bill]

Hi ,

I have two STS 54500 systems.

System 1 consists of:

1. GPS CLOCK   ST3E/LN HLDModel 54591
2. ClOCK   STE3T/HModel 54522
3.INPUT T1 Model 54511
4. ALARM   Model 54560 
5. IMUModel 54550
6. O/P T1Model 54571
7. OUTPUT NTS  Model 54580
8. STS 54500 card rack

System 2 consists of:

1. GPS CLOCK   ST3E/LN HLDModel 54591
2  ALARM   Model 54560 
3. IMUModel 54550
4. O/P T1Model 54571
5. OUTPUT NTS  Model 54580
6. STS 54500 card rack

The card rack weigh ~ 17 Lbs with the cards ~ 1.5 lbs each.
The systems are of very good  to excellent  cosmetic condition.
I have no info on their operational condition, but from their looks, I suspect 
they work.
There are no burns, dents or cut and jumpers.

I am asking $ 470.00 for system 1 and $ 370.00 for system 2. This includes 
shipping in contentinal US. Free shipping. No foreign.
Search CXR Larus on Ebay and you will see that this is a great price. Ebay is 
asking that much for one card.
If no response in two weeks, I plan on putting on Ebay.

If you are interested, contact me offline. I can send pictures.

Bill Reed
br...@otelco.net

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Re: [time-nuts] TAPR TICC boxed (input protection)

[Bob kb8tq]

Hi

One interesting “feature” of leakage specs: 

They often reflect the measurement limit rather than the actual device 
performance. If they
are guaranteed by test, the limit may be orders of magnitude above the actual 
performance. 

That’s on top of the likely “rated at max temperature” part that is relatively 
easy to understand. 
(A measurement at 125C will show a lot more leakage than one at 25 C).

Often measuring a representative sample under reasonable conditions is the only 
way to come
up with useful information. 

Bob

> On Apr 2, 2017, at 5:12 PM, Charles Steinmetz  wrote:
> 
> The FJH1100 is specified for reverse leakage of 10pA at 15v (which is also 
> the absolute maximum working voltage), and 3pA reverse leakage at 5v.  
> Junction capacitance is 2pF.  They cost $8.90 each at Mouser.
> 
> The B-C junction of an MPSH10 or MMBTH10 (SMT version) has only half as much 
> reverse leakage current (5pA) at a higher reverse voltage (20v).  I just 
> measured a few MPSH10s at 5v, and they showed less than 1pA reverse leakage. 
> The maximum working voltage is 30v and junction capacitance is 0.7pF.  
> Switching times are 5-10x faster than the FJH1100.  MMBTH10s cost $0.22 each 
> at Mouser.  MMBT5179s (SMT version of 2N5179) are very similar and cost $0.26 
> each at Mouser.
> 
> I have used the B-C junctions of BJTs and the gate junctions of JFETS as 
> low-leakage diodes for many, many years, for exactly these reasons (better 
> performance than "ultra low leakage" signal diodes and *much* lower cost).
> 
> Best regards,
> 
> Charles
> 
> 
> On 3/31/2017 9:39 PM, Alex Pummer wrote:
>> FJH1100
>> Ultra Low Leakage Diode
>> 
>> Alex
>> 
>> 
>> On 3/31/2017 6:00 PM, Charles Steinmetz wrote:
>>> Mark wrote:
>>> 
 I thought about using the clamp diodes as protection but was a bit
 worried about power supply noise leaking through the diodes and
 adding some jitter to the input signals...
>>> 
>>> It is a definite worry even with a low-noise, 50 ohm input, and a
>>> potential disaster with a 1Mohm input.  Common signal diodes (1N4148,
>>> 1N914, 1N916, 1N4448, etc.) are specified for 5-10nA of reverse
>>> current.  Even a low-leakage signal diode (e.g., 1N3595) typically has
>>> several hundred pA of leakage.  Note that the concern isn't just power
>>> supply noise -- the leakage current itself is quite noisy.
>>> 
>>> For low-picoamp diodes at a decent price, I use either (1) the B-C
>>> diode of a small-signal BJT, or (2) the gate diode of a small-geometry
>>> JFET. A 2N5550 makes a good high-voltage, low-leakage diode with
>>> leakage current of ~30pA.  Small signal HF transistors like the MPSH10
>>> and 2N5179 (and their SMD and PN variants) are good for ~5pA, while
>>> the gate diode of a PN4417A JFET (or SMD variant) has reverse leakage
>>> current of ~1pA (achieving this in practice requires a very clean
>>> board and good layout).
>>> 
>>> I posted some actual leakage test results to Didier's site, which can
>>> be downloaded at
>>> .
>>> This document shows the connections I used to obtain the data.
>>> 
 The TICC doesn't have the resolution for it to matter or justify a
 HP5370 or better quality front end. I'll probably go with a fast
 comparator to implement the variable threshold input.
>>> 
>>> Properly applied, a fast comparator will have lower jitter than the
>>> rest of the errors, and is an excellent choice.  Bruce suggested the
>>> LTC6752, which is a great part if you need high toggle speeds (100s of
>>> MHz) or ultra-fast edges.  But you don't need high toggle rates and
>>> may not need ultra-fast edges. Repeatability and stability are more
>>> important than raw speed in this application.  The LT1719, LT1720, or
>>> TLV3501 may work just as well for your purpose, and they are
>>> significantly less fussy to apply.
>>> 
>>> Note that the LTC6752 series is an improved replacement for the
>>> ADCMP60x series, which itself is an improved replacement for the
>>> MAX999.  Of these three, the LTC6752 is the clear winner in my tests.
>>> If you do choose it (or similar), make sure you look at the
>>> transitions with something that will honestly show you any chatter at
>>> frequencies up to at least several GHz.  It only takes a little
>>> transition chatter to knock the potential timing resolution of the
>>> ultra-fast comparator way down.  Do make sure to test it with the
>>> slowest input edges you need it to handle.
>>> 
>>> Best regards,
>>> 
>>> Charles
> 
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[time-nuts] HP5061B Peak to Valley Ratios

[cdelect]

Donald,

I agree with John, remove the gearing gizmo from the 10811 assy. the
adjust hole lines up any way so no need to drill a hole. you just need a
long insulated tuning tool. Also agree that a quick indication of tube
operation can be seen if the beam current rises when the mod is turned
off.

The Cesium tube test, set seen in
http://leapsecond.com/corby/HP-5071A-with-5061A-4.docx
is essentially a stand alone low frequency coil test. If I can't get a
decent LF coil beam current I scrap the tube as it's a waste of time to
put in in a unit and try the RF tests.

The test set uses a 555 based oscillator.

For low frequency tests in an instrument I use a 651B or 204C.

Set the amplitude and frequency for a peak on the beam current, make sure
mod is off and that you are on the central peak.

The figure of merit test in the manual will give an indication of how
well the tube and instrument are working, but a definitive test is to
perform an Allan deviation of the unit.

Cheers,

Corby

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Re: [time-nuts] TAPR TICC boxed

[Bob kb8tq]

Hi

If need it, indeed coming up with individual delays is a bit of a pain. One of 
the most basic decisions is to establish a reference plane. More or less - the 
signal at “this point” is zero. Everything else is going to be off by 
nanoseconds from that point (with meter long cables involved). It’s not 
impossible to set up, but it does take some discipline and care. The specific 
process is unique to the “time nut” side of things rather than the “frequency 
nut” side. 

We often ignore this sort of thing, but it can indeed be a very big deal. Some 
“cables” have very long delay numbers. Propagation from a radio beacon is one 
example. Packet coding / decoding delay on a digital data stream is another 
very common one. 

Bob

> On Apr 2, 2017, at 3:22 AM, Bruce Griffiths  
> wrote:
> 
> Its usually not possible to uniquely assign individual channel delays in this 
> way, however swapping cables allows the cable delay mismatch to be eliminated 
> from the measurement of the differential delay between channels.
> Eliminating the effect of cable delay mismatch can be useful when adjusting 
> narrowband quadrature splitters ect.
> 
> Bruce
>> On 02 April 2017 at 13:38 Mark Sims  wrote:
>> 
>> 
>> The new TICC support in Lady Heather has an "autotune" function that can 
>> null out the cable and channel delays.  You connect a signal (like 1PPS) to 
>> both channels through matched cables (like via a T adapter) and it averages 
>> the difference and sets the "FUDGE" factor for one of the channels to null 
>> out the net offset.  It doesn't null each channel individually.You might 
>> be able to swap the cables and work out how to allocate the offset to each 
>> channel.My unit has a channel offset of -305 ps (part of which could be 
>> due to mismatches in the "T" cables / connectors).
>> 
>> Autotune also calculates the FIXED TIME2 values if you want to play with 
>> that feature which can allegedly reduce the device noise by sqrt(2).  I'm 
>> not sure how well that works since the TIME2 values do drift over time and I 
>> don't know how much of an error in the TIME2 settings affects the device 
>> enough to make it perform worse than with the default automatic TIME2 mode.
>> 
>> -
>> 
>>> The whole delay difference thing does get into a “do you care?” sort of 
>>> category. The 
>> testing process you are doing may well calibrate out (or ignore) an offset 
>> of this nature. 
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Re: [time-nuts] TAPR TICC boxed

[Bruce Griffiths]

Its usually not possible to uniquely assign individual channel delays in this 
way, however swapping cables allows the cable delay mismatch to be eliminated 
from the measurement of the differential delay between channels.
Eliminating the effect of cable delay mismatch can be useful when adjusting 
narrowband quadrature splitters ect.

Bruce
> On 02 April 2017 at 13:38 Mark Sims  wrote:
> 
> 
> The new TICC support in Lady Heather has an "autotune" function that can null 
> out the cable and channel delays.  You connect a signal (like 1PPS) to both 
> channels through matched cables (like via a T adapter) and it averages the 
> difference and sets the "FUDGE" factor for one of the channels to null out 
> the net offset.  It doesn't null each channel individually.You might be 
> able to swap the cables and work out how to allocate the offset to each 
> channel.My unit has a channel offset of -305 ps (part of which could be 
> due to mismatches in the "T" cables / connectors).
> 
> Autotune also calculates the FIXED TIME2 values if you want to play with that 
> feature which can allegedly reduce the device noise by sqrt(2).  I'm not sure 
> how well that works since the TIME2 values do drift over time and I don't 
> know how much of an error in the TIME2 settings affects the device enough to 
> make it perform worse than with the default automatic TIME2 mode.
> 
> -
> 
> >  The whole delay difference thing does get into a “do you care?” sort of 
> > category. The 
> testing process you are doing may well calibrate out (or ignore) an offset of 
> this nature. 
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[time-nuts] TAPR TICC boxed

[Mark Sims]

The new TICC support in Lady Heather has an "autotune" function that can null 
out the cable and channel delays.  You connect a signal (like 1PPS) to both 
channels through matched cables (like via a T adapter) and it averages the 
difference and sets the "FUDGE" factor for one of the channels to null out the 
net offset.  It doesn't null each channel individually.You might be able to 
swap the cables and work out how to allocate the offset to each channel.My 
unit has a channel offset of -305 ps (part of which could be due to mismatches 
in the "T" cables / connectors).

Autotune also calculates the FIXED TIME2 values if you want to play with that 
feature which can allegedly reduce the device noise by sqrt(2).  I'm not sure 
how well that works since the TIME2 values do drift over time and I don't know 
how much of an error in the TIME2 settings affects the device enough to make it 
perform worse than with the default automatic TIME2 mode.

-

>  The whole delay difference thing does get into a “do you care?” sort of 
> category. The 
testing process you are doing may well calibrate out (or ignore) an offset of 
this nature. 
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