[time-nuts] Vanguard TCXO

[Thomas Allgeier]

Hello All,

This is for the medium-precision nuts amongst us. I have invested £14.50 
in one of these Vanguard 0.1ppm TCXO's to pimp my Siglent FG which has a 
footprint for it. It is its internal ref at 25 MHz. The swapping-in was 
simple to do and the FG works fine with it. Since it has a counter mode 
I did a quick check to show whether it was worthwile: I made it count 
the 10 MHz from my Proteus GPSDO. The Siglent reads to 1 Hz and straight 
after turn-on it went straight to 10.00 MHz. Over about 1 day I 
never saw it more than +/-1 Hz off, and this involved a deliberate 
temperature change of just over 5 deg C, basically by having the heating 
in the room off and on. For most of the time the display sat solidly at 
10.00.


So, to summarise, in a rough sort of way the thing lives up to its 
0.1ppm spec, at least around the 20C temperature mark. I bought it from 
a Hong Kong seller on Ebay - naturally there is always a chance that 
other devices sold with the same description/label might not perform as 
well.


I'm quite aware that the generator (DDS) suffers from other sources of 
error, which won't be improved by the clock being better, but at least 
the nominal frequencies it outputs are now going to be very close to the 
mark without the need for an external ref.


Kind regards,

Thomas.

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[time-nuts] Quartz Technik Xtal

[Thomas Allgeier]

Time-nuts,

I have a 100 kHz Quartz Technik crystal oscillator with matching socket. It
comes from a Hartmann / Grundig frequency counter (surely it was the
timebase). 1950s/60s I expect.

If anybody has a use for this it's yours for the shipment cost. (Currently
located in the UK).

Best regards,
Thomas.
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Re: [time-nuts] 5370B Input Board Repair [WAS: 5370B Question / help needed]

[Thomas Allgeier]

Hi Don,

Yes, my thinking is they may have feared problems and opted for the 
adhesive, but I'm only guessing. Wouldn't have been my first choice for this 
piece of kit.


I don't think you can get this stuff off one joint at a time, but definitely 
one component at a time which is what I have done. The adhesive is 
physically between the component and the pads and unless the component is 
removed you won't be able to clean up the pad ready for soldering. After all 
this messing about with these SMD's it is probably better fitting new parts 
anyway, otherwise you may well be back into the intermittent fault situation 
fairly quickly.


Kind regards,
Thomas.

Message: 6
Date: Wed, 19 Jul 2017 18:16:42 -0600
From: djl 
To: Discussion of precise time and frequency measurement

Subject: Re: [time-nuts] 5370B Input Board Repair [WAS: 5370B Question
/ help needed]
Message-ID: <2138b5104f5a250430c2ed46a755d...@blackfoot.net>
Content-Type: text/plain; charset=UTF-8; format=flowed

Could it be that someone thought adhesive would be less prone to
cracking from stress than solder?
Also, do you think that the adhesive could be cleaned one end at a time
and replaced with solder?
I'm admittedly too lazy to look/try just now.
Don



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Re: [time-nuts] 5370B Input Board Repair [WAS: 5370B Question / help needed]

[Thomas Allgeier]

Hello Gary,

The adhesive doesn't come off with solvent - I am afraid very careful 
scraping with a pointy scalpel under the microscope was what did it. That's 
what makes me think it is epoxy-based. Touching it with a hot iron also 
doesn't seem to have much effect. Once cured it probably can only be 
mechanically removed. But it is not immensely strong, I guess the metal 
filler means it can be kind of crumbled off bit by bit. Make sure you really 
get all the debris removed as of course it is conductive and would easily 
cause trouble elsewhere.


I hope you get yours going!

Kind regards,
Thomas.

Message: 3
Date: Wed, 19 Jul 2017 07:09:58 -0600
From: Gary Neilson 
To: time-nuts@febo.com
Subject: Re: [time-nuts] 5370B Input Board Repair [WAS: 5370B Question
/ help needed]
Message-ID: 
Content-Type: text/plain; charset=utf-8; format=flowed

This is very interesting, I have a 5370B that has the same behavior as
yours. I will take the input board out again and give it a good
inspection. BTW, what did you use to clean the adhesive from the pads ?

Thanks
Gary


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[time-nuts] 5370B Input Board Repair [WAS: 5370B Question / help needed]

[Thomas Allgeier]

Hello All Again,



I’ve got my 5370B going now and in the process made a “discovery” which I 
thought might be worth sharing:

The A3 input board is a through-hole PCB with a few SMD capacitors and 
resistors on the reverse of the “switch area”. It turns out that on my 5370 
(2410A00777) these components are not soldered, but fitted with conductive 
adhesive. I first thought it was solder with a black coating but under a 
microscope it is clear that it is not solder at all. Most probably it is a 
mixture of epoxy and silver particles, or a similar compound. So no going over 
joints with a fine iron…

Inspecting all this carefully under the microscope I discovered that the 
“joints” on 2 resistors (R23 and R56) had cracked. As you know this board gets 
heat from the hybrid amplifier IC’s and due to the way the board is mounted to 
the front panel I guess it sees thermal stressing when the instrument warms up 
and cools down. While this obviously lasts a long time it looks that on my unit 
the adhesive has eventually cracked in places. (Vigorous switch activation and 
pressing / pulling on the switch handles also won’t be helpful in this 
respect…) One of the resistors just fell off at the slightest touch with fine 
tweezers.



Anyhow, after removing the offending components, cleaning the pads of the 
adhesive, and soldering replacements in place, we have a perfect 99.9x ns with 
the 10 MHz on the commoned inputs. Happy days!



So if any of your 5370’s have the kind of intermittent fault I described (and 
one or two other people seem to have reported) or instability that seems to 
originate from the A3 board – check the joints around the SMD’s.



I wonder why / how it ended up having the adhesive instead of solder – were 
earlier / later instruments the same, or was this a build change introduced at 
a certain period?



Hope the above is of help to somebody else,

Thomas.



Message: 1
Date: Sat, 15 Jul 2017 21:54:47 +0100
From: Thomas Allgeier <th.allge...@gmail.com>
To: Discussion of precise time and frequency measurement
<time-nuts@febo.com>
Subject: Re: [time-nuts] 5370B Question / help needed
Message-ID:

Re: [time-nuts] 5370B Question / help needed

[Thomas Allgeier]

Hello Folks,

I'm coming back to this after a few days of prodding etc. and there has
been some progress. The fault has been tracked down to the A3 input board
and it points at a crack in the board or a joint. Here is the sketch:
After a good clean of the switches and re-seating all boards etc. the 5370
sprung back into life with almost-in-spec performance of 102.xx ns with
it's own 10 MHz. Trouble is it didn't last - after a while and triggered by
sliding some switches around it went back to the 14 ns. Fiddling with the
BNC's may have the same effect, i.e. there is a mechanical element to it
all.
Turns out that running it with the front panel removed I can make it go
from 14 to 102 ns by slightly bending the A3 board, certainly while it is
cold. After a while this trick doesn't work anymore, my suspicion is
whatever crack/gap is causing the trouble has expanded too far to close it
tight. After cool-down we're back to square one.
I notice there are a few SMD components on that board, right in the middle
where it would bend most - basically on the reverse side of the switches.
Capacitors and resistors I expect. I wonder if it is worth going over the
solder joints of all these carefully.
What has stopped me so far are 2 questions:
Am I the only one with this observation or has anybody come across this
before?
Secondly the solder on these SMD's is coated with a black substance.
Clearly this could be removed somehow but it is probably there for a
reason. Has anybody re-touched joints like these before?
On an instrument like this it is very much a case of "proceed with care"
and I'd hate to do more damage by rushing in.

On a related subject: last year there was a discussion over redesigning the
input board(s) for the 5370 / 5345. Did this get off the ground? If my A3
packs up completely...

Thanks in advance for any suggestions,

Thomas.


Date: Wed, 5 Jul 2017 11:00:35 +0100
From: "Thomas Allgeier" <th.allge...@gmail.com>
To: <time-nuts@febo.com>
Subject: Re: [time-nuts] 5370B Question / help needed
Message-ID: <f2c3025c50df4411a8ec836c55b8e...@flintec.uk>
Content-Type: text/plain; format=flowed; charset="UTF-8";
reply-type=original

Thanks all for your help and suggestions - I've been off grid for the last
few days.
I will look into the dust/contacts issue first, and sweat up on the manual
and archive posts in relation to the adjustment procedure.
Then I will try to see how far this gets me and report back - watch this
space as they say.

I may well need the extender cards but since I am based in the UK shipment
would have to be considered. Probably worth checking all other options
first.

Best regards,
Thomas.
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Re: [time-nuts] 5370B Question / help needed

[Thomas Allgeier]

Thanks all for your help and suggestions - I've been off grid for the last 
few days.
I will look into the dust/contacts issue first, and sweat up on the manual 
and archive posts in relation to the adjustment procedure.
Then I will try to see how far this gets me and report back - watch this 
space as they say.


I may well need the extender cards but since I am based in the UK shipment 
would have to be considered. Probably worth checking all other options 
first.


Best regards,
Thomas.


Message: 1
Date: Mon, 3 Jul 2017 08:13:09 -0600
From: Gary Neilson <g...@deepskyridge.com>
To: time-nuts@febo.com
Subject: [time-nuts] Fwd:  5370B Question / help needed
Message-ID: <0b65d3e6-c8d0-9eb8-fc70-f36c25ca8...@deepskyridge.com>
Content-Type: text/plain; charset=utf-8; format=flowed

I have a 5370B from ebay, it was missing a couple of boards and had a
bad interpolator card. Also a bad input hybrid on the stop channel.

My unit acts similar to yours, TI measurement on the 10mhz signal shows
107 ns.

Frequency and Period measurement is spot on.

I think it needs an alignment performed. I will get to that soon.

Good Luck

Gary - K5DSR



 Forwarded Message 
Subject: [time-nuts] 5370B Question / help needed
Date: Sat, 1 Jul 2017 21:12:27 +0100
From: Thomas Allgeier <th.allge...@gmail.com>
Reply-To: Discussion of precise time and frequency measurement
<time-nuts@febo.com>
To: Discussion of precise time and frequency measurement
<time-nuts@febo.com>



I got hold of a 5370B cheaply but it turns out it may have a fault:

Going through the motions of measuring TI with it's own 10MHz ref as input
(as described in the manual) I don't get 100 ns, but around 15 ns. So this
is with the switch set to START COM. Oddly enough I get the same 15 ns with
the switch set to SEP, and going through a 6 ft cable between start and
stop.

Now I can "tune" the thing to display 100 ns by changing the trigger
levels. Start at 0.6 V and stop at -0.1 V will achieve this. Once again
this does not change by going from COM to SEP i,e. by adding the 6 ft delay.

One other observation, probably related: After powerup it took several
vigorous switch activations of the COM/SEP switch before the thing swung
into action at all - i.e. the first reaction with COM setting was an Err
02, and with SEP I got the 15 ns as described above. So that switch may be
a bit dodgy.

Measuring in frequency mode gives the 10 MHz quite accurately, less than
1mHz off with its own ref as stop input. Feeding the 10 MHz in from my
GPSDO also ties up OK, it is around 40mHz off with perhaps 5-10mHz jitter.

Has anybody come across anything similar? I couldn't find much in that vein
in the archive but may have overlooked something. The one thing I was
worried about at first was the heat sinks at the rear getting really hot
but it seems I'm not the only one with that observation.

To some extent it looks like the input levels for triggering are off, but
then the fact that the 6 ft cable don't show up as extra delay may mean
there is something else wrong.

Looks like some "fun with Bill and Dave" lies ahead if somebody can point
me in the right direction.

Thanks in advance,
Thomas.

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Re: [time-nuts] 5370B Question / help needed

[Thomas Allgeier]

Yes, they are both set to "positive".  Leaving the start at "pos" and
switching the stop to "neg" gives 66 ns. One more observation, which
probably does make sense: If I set the ARming to +/-TI and toggle the
Period Complement the "sum" is always very close to 100ns: 15 is
complemented by -85 and 66 by -34. All this is for Trigger Levels at Preset.

When I "tune" the levels to get 100 ns at +TI and then switch to +/-TI I
get around 20 ps, and the Complement button has no effect on this.

On Sat, Jul 1, 2017 at 9:38 PM, Poul-Henning Kamp <p...@phk.freebsd.dk>
wrote:

> 
> In message <CAOT1cQJ4K8uyNvFp8AjoLGjd57Pm31LnZT_jRo44J4Zhesvgzg@mail.
> gmail.com>, Thomas Allgeier writes:
>
> >Going through the motions of measuring TI with it's own 10MHz ref as input
> >(as described in the manual) I don't get 100 ns, but around 15 ns. So this
> >is with the switch set to START COM. Oddly enough I get the same 15 ns
> with
> >the switch set to SEP, and going through a 6 ft cable between start and
> >stop.
>
> Have you checked the trigger polarities ?
>
>
> --
> Poul-Henning Kamp   | UNIX since Zilog Zeus 3.20
> p...@freebsd.org | TCP/IP since RFC 956
> FreeBSD committer   | BSD since 4.3-tahoe
> Never attribute to malice what can adequately be explained by incompetence.
>
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[time-nuts] 5370B Question / help needed

[Thomas Allgeier]

I got hold of a 5370B cheaply but it turns out it may have a fault:

Going through the motions of measuring TI with it's own 10MHz ref as input
(as described in the manual) I don't get 100 ns, but around 15 ns. So this
is with the switch set to START COM. Oddly enough I get the same 15 ns with
the switch set to SEP, and going through a 6 ft cable between start and
stop.

Now I can "tune" the thing to display 100 ns by changing the trigger
levels. Start at 0.6 V and stop at -0.1 V will achieve this. Once again
this does not change by going from COM to SEP i,e. by adding the 6 ft delay.

One other observation, probably related: After powerup it took several
vigorous switch activations of the COM/SEP switch before the thing swung
into action at all - i.e. the first reaction with COM setting was an Err
02, and with SEP I got the 15 ns as described above. So that switch may be
a bit dodgy.

Measuring in frequency mode gives the 10 MHz quite accurately, less than
1mHz off with its own ref as stop input. Feeding the 10 MHz in from my
GPSDO also ties up OK, it is around 40mHz off with perhaps 5-10mHz jitter.

Has anybody come across anything similar? I couldn't find much in that vein
in the archive but may have overlooked something. The one thing I was
worried about at first was the heat sinks at the rear getting really hot
but it seems I'm not the only one with that observation.

To some extent it looks like the input levels for triggering are off, but
then the fact that the 6 ft cable don't show up as extra delay may mean
there is something else wrong.

Looks like some "fun with Bill and Dave" lies ahead if somebody can point
me in the right direction.

Thanks in advance,
Thomas.
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Re: [time-nuts] Counter?

[Thomas Allgeier]

Hi All,

An interesting find, but not as old as advertised: Friesecke & Hoepfner only 
moved to Erlangen-Bruck after WW2, in or around 1949. During the war they 
were in Berlin I think. They made quite a range of stuff, one of their main 
post-war activities was radioactivity measurements i.e. counters.

The thing looks 1960's to me. Not sure if it is worth 3000 bucks, though.

Kind regards,
Thomas.


Date: Thu, 18 Feb 2016 23:32:09 +0100 (CET)
From: "iov...@inwind.it" 
To: 
Subject: [time-nuts] Counter?
Message-ID:
<1178303383.10543371455834729338.javamail.ht...@webmail-46.iol.local>
Content-Type: text/plain; charset=UTF-8

This tube type item on ebay is equipped with E1T high speed decade counting 
tubes.

222022951573

I'm not affiliated,  etc...
Antonio i8iov



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[time-nuts] Navsymm Proteus GPS CDU Software

[Thomas Allgeier]

Hello Time-Nuts,



I have recently come into possession of a Navsymm Proteus GPS Time and 
Frequency Generator. Also known under Navstar Systems. There have been various 
postings about this piece of kit, in some of which there was a mention of the 
CDU software which allows to configure it.



The thing powers up but does not lock on. The manual says this could be the 
case if it was moved since last locked and it may need configuring.



To cut a long story short, does anybody have the CDU software and could it be 
“shared”? It seems to need an old-style PC but that won’t be a problem around 
here.



I will meanwhile check if any sense can be made of its outputs, in case there 
is some hardware problem.



Thanks in advance,

Thomas.
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[time-nuts] More results with the ACAM GP22 chip

[Thomas Allgeier]

Hello Time-Nuts,

I can now add a few more results from "Range 2" of the ACAM GP22 TDC chip.

As before they can be found here:  www.stanton-instruments.co.uk/page26.html

The first 2 files are more or less a repeat of what I did for "Range 1" except 
using a 250 m RG6 coax spool as delay line. In a departure from the original 
plan I left the whole length intact as one continuous piece. This gives pretty 
much 1 µs delay, a little less than predicted, and the noise band is around 1 
ns wide. I must add that it was somewhat tricky to tune the system to get this 
as the waveform out of the un-buffered line is not so nice. The output level 
from the signal generator has to be set just right for the GP22 to trigger, the 
only reliable setting is a "falling edge" and when the scope is connected at 
the same time the noise is several times worse.

So I pinned high hopes on Bob Camp's suggestion to use a 74ACT14 hex Schmitt 
trigger to buffer the line - which I did and results from which are given in 
the second pair of files.

In a nutshell, this changed very little to the "noise outcome" of 1 ns but made 
the whole affair much easier to "tune", since of course now I have clean 
waveforms. It makes little difference now whether "falling" or "rising" is 
selected in the chip's software.

The Schmitt trigger as expected increases the delay a little, so we have around 
1100 ns, and it also seems to add noise if not powered exactly in its sweet 
spot of around 5.02V. As little as 50 - 100 mV higher or lower will add several 
ns of extra noise. In some cases having the scope hooked on also added noise, 
but not as much as with the direct approach of using the coax line only. The 
74ACT shows around 20 ns between in and out (double-inverted as suggested by 
Bob) which may depend a little on Vcc and probably has some jitter of its own 
even with constant supply.

As before we have a minor frequency dependency, but less so: I have used a 
74ACT14 before and after the line, which should have given more consistent rise 
times as compared to the "raw" output from my Thandar sig-gen.

A long story cut short: With crude and noisy kit you can expect to time a 
period to within 1ns in range 2 of the GP22, assuming that the noise level does 
not increase for longer periods. And also allowing for the fact that this is 
all based on a 32kHz "master clock" on the evaluation board. Which of course 
could be done differently and with higher precision if needed.

This applies to no averaging being selected in the chip's software. If speed is 
not essential and you can wait to average 2 or even 10 cycles the whole noise 
thing goes pretty much away, which of course is pretty clear from the results 
plots.

I hazard a guess: The fact that the noise level in the "best case" scenario 
comes out the same with and without the buffers indicates to me that on the 
inputs of the GP22 are effectively similar Schmitt triggers to what I have used 
externally.

I hazard a second guess: If you hooked a very precise and stable frequency 
source as an input onto the GP22 and did it in a way that keeps the signals 
clean the claims of 50 ps "resolution/stability" could probably be achieved 
even into the µs range. The 250 m spool sitting on my floor and all the very 
crude connections don't fill me with confidence. (In the ns range I got the 50 
ps pretty much already with the crude setup as per the initial results.)

Which means for what I have in mind the chip is adequate, and what I saw 
initially (10's to 100's of ns noise) is simply the oscillator on the weighing 
cell trying to keep itself tuned with the mechanical vibrations which it is 
meant to lock on to.

Best regards,
Thomas.
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[time-nuts] First results with the ACAM GP22 chip

[Thomas Allgeier]

Hello Time-Nuts,

As threatened in earlier postings I can now show some results gathered with the 
ACAM GP22 TDC chip and evaluation board. Admittedly this is only from its 
"range 1" at the moment.

The setup was suitably simple to match my almost non-existent level of 
expertise and available kit: I have a very old analogue Thandar function 
generator. This I set to frequencies of 1, 10, 100, 1000 and 1 Hz 
square-wave. Its adjustable 50 Ohm output was fed into a short bit of coax 
cable which at its other end was connected to the start pin of the GP22. The 
same output also fed into a 5 metre length of coax cable which was connected to 
the stop pin. Both cables were terminated with 75 Ohms (the cable was 75 Ohms 
as well), and 2 scope channels were hooked up to these pins so I could see what 
I was doing.

As the theory predicts I got a delay of around 24 ns and the GP22 measured this 
with a "double" resolution of around 50 ps. Recordings were made of 1000 
samples each at these 5 frequencies and dumped into Excel spreadsheets. No 
averaging was selected on the GP22, so these are 1 shot samples.

Not to overload everybody's inbox I have uploaded the files to my homepage: 
www.stanton-instruments.co.uk/page26.html

(Those not interested in old balances ignore the rest of the website. Those not 
interested in the GP22 performance ignore the whole link.)

At 10 Hz I let the whole setup run for 30 minutes which gives around 64000 
samples, the limit of the eval software supplied with the kit. Again a 
spreadsheet was compiled with those values.

It certainly looks pretty good to me - if the chip does the same in range 2 I'd 
be quite happy. Short term nearly all readings are within the 100 ps band. Over 
the half hour that band is wider but there appears to be no measurable drift. 
There was no temperature control, other than the stuff just sitting on my desk 
with the heating on in the house. That said I don't think there was more than 
one degree C change over the whole duration of the experiment.

There seems to be some frequency dependency as the absolute values of the 
measured delay are not identical. But then there is a good chance that the rise 
time of the function generator also varies a little with the selected 
frequency, and I suppose this would be enough to explain the small differences 
- surely my delay line will react to that.

Incidentally a very large reel of RG6 coax is supposed to arrive some time next 
week. The intention is to cut a length to give somewhat over 500 ns delay and 
repeat the entire palaver in range 2. If this proves successful I will try it 
with the full reel (250 m). I don't intend to push it any further, I would 
expect the performance of the chip to be similar whether the period to be 
measured in 1 µs or 70.

Thanks again for all the suggestions so far.

Best regards,
Thomas.
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Re: [time-nuts] ACAM GP22 Chip

[Thomas Allgeier]

Hello Angus,

That is roughly what I want to do, a plausibility check if what I see is 
caused more by the GP22 or already present on the signal I am trying to 
measure.
Very clearly there is no principal problem, the data I get from the GP22 is 
pretty decent and with enough filtering already useable. I have the feeling 
the GP22 does not add very much noise/jitter and all I want is get a handle 
on how much in reality.


If we take this approach further we will have to invest in some additional 
kit, but apart from that I am also rather taken by the capabilities of the 
GP22 as a timer, and my own curiosity wants to find out how good a homebrew 
counter/timer could be built from it.


As I said I will feed back anything I can establish in this respect.

Best regards,
Thomas.

-Original Message- 
From: Angus

Sent: Thursday, November 26, 2015 1:54 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] ACAM GP22 Chip



I wouldn't expect the noise to
be in the ns range, but i wouldn't surprised if it was a few 10ps.
I have never done any measurements though, and I don't think i've
ever seen any jitter measurements for 32kHz oscillators, so take
this value as rough guestimate.


On the GP21 board I used it was more like 10ns+. I don't know if
that's typical, but it wasn't a even particularly cheapo crystal as
the original one was faulty and I had to replace it. The official acam
board might be better, but the data sheet specifically talks about the
32K osc having a lot of jitter.

One of the problems of the data sheet is that it is really tailored
for those using it as a flow converter - some of the text does not
even make sense otherwise. That was one of the reasons I was planning
to test it more as a TDC, but just getting back to doing that now.

Angus.
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Re: [time-nuts] ACAM GP22 Chip

[Thomas Allgeier]

Hello Tom,

One of the problems here (embarrassingly) is that we have a lack of kit in 
this particular respect. And I am not yet prepared to throw too much money 
at it before I can judge the real potential.
(Our forte so far is high precision in terms of voltage and current, which 
is what you traditionally need for strain gauge measurements, which is what 
we have been traditionally doing. nV instead of ns or ps so to speak.) Hence 
the low-tech approach, and having read the tests on the HP5370 I thought 
"hey, I can do that".


Anyway we need the results a lot quicker than 1 Hz, ideally at least every 
10 ms or so. The reason is that in weighing much is achieved by filtering 
and if you want a reasonable response time after the filter then you have to 
feed in the raw stuff quite quickly. The GP22 seems to be pretty much what 
is needed, and we happen to buy from ACAM already.


I played with it last night and I think I should shortly be in a positions 
to share "early" findings.


Best regards,
Thomas.



-Original Message- 
From: Tom Van Baak

Sent: Thursday, November 26, 2015 12:02 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] ACAM GP22 Chip


In order to evaluate the chip I was planning to replicate John A’s
experiment with the coaxial delay line from the HP5370b

For those wondering: "John A" is John Ackermann and the experiment
in question is documented at http://www.febo.com/pages/hp5370b/


Maybe I misunderstand, but I would not suggest testing a time interval 
counter by using a fixed ns delay -- that's almost never how the real world 
works and those tests tend to produce bogus ADEV plots that have -1 slope 
forever (a clue that something's wrong with the test).


A selection of fixed delays is slightly better. But best, and much easier, 
is to use uncorrelated A, B, and LO (ext ref) signals. A fixed delay may 
land on a sweet spot or honey bucket. Linear sweeping the range covers all 
spots, and gives you best case / worst case / rms statistics as a bonus. In 
other words, what you want is a set of random (but known, or knowable) 
delays; not a set of hardcoded delays.



of the GP22 I need a delay of 500 ns or more (actually 1 µs sounds a 
better start).


Are you sure you want a hardcoded delay of N ns or N us? Or is a variable or 
even varying delay sufficient?


What I use in cases like this is two stable oscillators that slowly drift 
apart (i.e., close, but not the same frequency). For example, if they differ 
in frequency by 1e-12 your signals drift 1 ps/s. Or if they differ by 1e-10 
your signals drift by 1 ns / 10 s. You get an uncorrelated, very low-noise, 
linear phase sweep "for free".


This sort of slow varying phase relationship is ideal when making counter 
tests; much better than a fixed delay. You can use a laboratory counter to 
monitor their exact phase difference in parallel with your DUT. That is, you 
then compare TIC "truth" against what your DUT reports.



We want to use this chip to measure the period of a square wave, of around 
13 kHz i.e. in the 70 µs range.
As the application is potentially high-accuracy we need to know the period 
to within 1 ns or better.


I may have missed it in the thread -- but how quickly do you need your 
measurements? Is one measurement every 1 or 10 or 100 seconds ok? (in which 
case an ACAM chip is total overkill). Or is this some sort of sub-second 
real-time application that require both modest resolution (1 ns / 70 us = 15 
ppm, easy) and fast response (hard)?


/tvb
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Re: [time-nuts] ACAM GP22 Chip

[Thomas Allgeier]

Hello Hal,

The book has been sourced and is on its way to me - a good pointer, thanks. 
With it and the comments I have had from you guys I expect I will get pretty 
much what I want, given a little time which thankfully I have.


I will report back any outcome that looks plausible / presentable.

Kind regards,
Thomas.
- Original Message - 
From: "Hal Murray" 
To: "Discussion of precise time and frequency measurement" 


Cc: 
Sent: Tuesday, November 24, 2015 7:44 PM
Subject: Re: [time-nuts] ACAM GP22 Chip




th.allge...@gmail.com said:
I should say from the start that I am new to time and frequency 
measurements

and not even an electronics engineer – but then I have been exposed to
high-precision electronics for the last 25 years hence have picked up 
some

dangerous degree of half-knowledge.


Do you have a copy of Art of Electronics by Horowitz and Hill?



In order to evaluate the chip I was planning to replicate John A’s
experiment with the coaxial delay line from the HP5370b – but as my 
interest
is in “measuring range 2” of the GP22 I need a delay of 500 ns or 
more

(actually 1 µs sounds a better start). This is the equivalent of a 200 m
length of cable. I fear trouble with this: Am I not getting unwanted
inductivities if I use a coil of that size?


The trick is that your coil has 2 wires.  It's a transmission line.

Here is the handwaving explanation: The current on the return path is 
going

in the other direction and cancels out the inductance.

Twisted pair will work almost as well as coax, maybe better than cheap 
coax.


AoE has an appendix on transmission lines.  You can find lots of info on 
the

web.  You need to terminate it.  You will want a scope to check the
termination.



--
These are my opinions.  I hate spam.



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Re: [time-nuts] ACAM GP22 Chip

[Thomas Allgeier]

Hello Bob,

That kind of approach is what I had in mind and as others have commented if 
done carefully (which for me means a bit at a time) should get me there.


The buffers may present a bit of a challenge to a mechanical engineer 
(unless they are the kind that can be salvaged from railway waggons) but the 
AoE book as suggested by Hal should set me straight.


Thanks again,
Thomas.
- Original Message - 
From: "Bob Camp" <kb...@n1k.org>
To: "Discussion of precise time and frequency measurement" 
<time-nuts@febo.com>

Sent: Tuesday, November 24, 2015 11:24 PM
Subject: Re: [time-nuts] ACAM GP22 Chip



Hi

If you head down to your local big box store, they will happily sell you a 
thousand foot spool
of RG-6 coax for next to nothing. If their prices are still to high, the 
auction sites will sell it for
even less. It has a 75 ohm impedance and a bandwidth of several GHz. The 
rather convent
formula of RT = 0.35 / BW then comes in. A 3.5 GHz cable will limit you to 
a 100 ps rise time.
In all likelihood, you will be unable to generate a signal with this fast 
a rise time.


You also will have some loss effects in the cable that are frequency 
dependent. The calculation above
assumes you have done a few tricks to take care of this. If not, to get a 
10 ns rise time, you need to maintain
a 35 MHz bandwidth. That works fine if you have a buffer every 500 feet. 
No tricks, just a CMOS buffer

chip.

As noted by others, it *is* coax. You need to drive it and terminate it 
with 75 ohms. At 35 MHz, a cheap
75 ohm resistor will do the trick just fine. At 3.5 GHz you may need to 
get a bit more careful.


So is the 500’ limit an issue? I’d suggest that it’s not. Consider 
chopping up the spool in a binary series of
400, 200,100,50,25,12.5, 6.5, 3.25 feet.  You now have a set of buffered 
lines that can be arranged to give you
a nice set of 256 time steps. Yes, the delay of the buffers will get in 
the way a bit. The actual line lengths will

be a bit shorter as the lengths drop.

So how much delay do you get from a 400’ line? Velocity factor comes in 
here. Best guess is that
your foam RG-6 has a 0.78 velocity factor. The "speed of light” in the 
coax is 78% of the speed of light
in vacuum. Your 400 foot coax has about a 520 ns delay. Your stack comes 
out just a bit over 1 us.


Bob



On Nov 24, 2015, at 9:04 AM, Thomas Allgeier <th.allge...@gmail.com> 
wrote:


Hello,



I have an ACAM GP22 TDC chip and evaluation board which I am looking at 
for “work” purposes – I work for a company active in the weighing and 
force measurement world.




I should say from the start that I am new to time and frequency 
measurements and not even an electronics engineer – but then I have been 
exposed to high-precision electronics for the last 25 years hence have 
picked up some dangerous degree of half-knowledge.




We want to use this chip to measure the period of a square wave, of 
around 13 kHz i.e. in the 70 µs range. As the application is potentially 
high-accuracy we need to know the period to within 1 ns or better.




In order to evaluate the chip I was planning to replicate John A’s 
experiment with the coaxial delay line from the HP5370b – but as my 
interest is in “measuring range 2” of the GP22 I need a delay of 500 ns 
or more (actually 1 µs sounds a better start). This is the equivalent of 
a 200 m length of cable. I fear trouble with this: Am I not getting 
unwanted inductivities if I use a coil of that size?




So, to come to the point: Am I pushing the concept of a coax delay too 
far with 1 µs and are there other (simple/reliable) ways to achieve this 
kind of delay? I have tried it with a shorter piece of cable (around 2 ns 
which is measured in “range 1”), there I seem to get consistency 
virtually to within 100 ps. But I need to know if the device sticks to 
this level of performance when the periods are much longer, and thus 
measured in “range 2”.




Thanks and best regards,

Thomas.
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Re: [time-nuts] ACAM GP22 Chip

[Thomas Allgeier]

Moin Attila,

You guessed my origin right from my name.

It is not that I don't trust ACAM (we are one of their customers) but from 
the source I am measuring I get a lot of what you guys probably call jitter. 
So I want to be sure the jitter comes from the oscillator I am measuring and 
not from the GP22.
Absolute accuracy is not the problem here, unless the 32768 Hz clock on the 
eval board actually drifts. In other words if we are 10 ns out on the period 
measurement nobody cares if it remains the same 10 ns all the time. As in 
many applications in the weighing industry what really matters is the change 
in weight, not how heavy the mass is in absolute terms.


It sounds like the coil must be wound what we used to call "bifilar" in my 
school days, i.e. self-cancelling the inductivity. That should be doable, 
and on the other stuff I will read up a bit first.


Thanks,
Thomas.
- Original Message - 
From: "Attila Kinali" <att...@kinali.ch>
To: "Discussion of precise time and frequency measurement" 
<time-nuts@febo.com>

Sent: Tuesday, November 24, 2015 4:56 PM
Subject: Re: [time-nuts] ACAM GP22 Chip



Moin,

On Tue, 24 Nov 2015 14:04:32 -
"Thomas Allgeier" <th.allge...@gmail.com> wrote:


We want to use this chip to measure the period of a square wave, of
around 13 kHz i.e. in the 70 µs range. As the application is potentially
high-accuracy we need to know the period to within 1 ns or better.


That's some modest requirement and should be doable with the GPS22
quite easily (or any other TDC for that matter). BTW: when specing
something like this, please make sure to mention whether 1ns is
1sigma, 3sigma or worst case/peak-to-peak. These 3 are quite different
requirements.


May I ask why you want to verify the specs of the GP22?
The specs say that it does something between 39ps and 70ps (1sigma),
which is probably way better than what you need. And as Acam is
a german company, I expect the datasheet to be accurate.

BTW: 1ns over 70us is approximately 14ppm. The GP22 uses the attached
crystal for absolute calibration. Please be aware that 14ppm will
require at least a TCXO to reach that level over the whole temperature
range, and depending on what TCXO you use, you might need to calibrate
the TCXO post-production and again after a couple of years of use.
Even if you don't need calibrate, I would add a TCXO frequency measurement
to the production test.

BTW2: the "we have a x ppm TCXO" value is usually misleading,
as that's the best-case, pre-soldering, pre-aging, pre-anything value.
The end-value can be 3 times as large... easily.
(unless you happen to choose one of the more honest manufacturers,
for example, like Abracon)


In order to evaluate the chip I was planning to replicate John A’s
experiment with the coaxial delay line from the HP5370b


For those wondering: "John A" is John Ackermann and the experiment
in question is documented at http://www.febo.com/pages/hp5370b/


– but as my interest
is in “measuring range 2” of the GP22 I need a delay of 500 ns or more
(actually 1 µs sounds a better start). This is the equivalent of a 200 m
length of cable. I fear trouble with this: Am I not getting unwanted
inductivities if I use a coil of that size?


The coax is a transmission line. Yes you have inductance and capacitance,
but it does not make that much sense to talk about that anymore,
the impedance is the right thing to talk about.
Your output will not be as sharp as your input due to dispersion,
but that can be easily recovered using some buffer gate.

Please make sure that your coil is reasonably temperature stabilized
and, if it's cheaper cable, also humidity stabilized, as both parameters
change your delay. (putting it into an isolated box should be good
enough for this kind of measurment).


Attila Kinali

--
It is upon moral qualities that a society is ultimately founded. All
the prosperity and technological sophistication in the world is of no
use without that foundation.
-- Miss Matheson, The Diamond Age, Neil Stephenson
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Re: [time-nuts] ACAM GP22 Chip

[Thomas Allgeier]

Dear Paul,

Thanks for the reply and thanks to all other contributors. Seems I have 
subscribed to the right list!


As it happens this is a sideline project. So I have the luxury to ask for 
advice and even consult books before advancing with care.


I will probably try and go down the coax route, starting with a shorter 
length first, and reading up a bit.
If any useable results can be obtained I will post them for future 
reference.


Best regards,
Thomas.
- Original Message - 
From: "paul swed" <paulsw...@gmail.com>
To: "Discussion of precise time and frequency measurement" 
<time-nuts@febo.com>

Sent: Tuesday, November 24, 2015 3:17 PM
Subject: Re: [time-nuts] ACAM GP22 Chip



Thomas
Welcome to the group. I am sure others will comment.
Many of us have a very wide range of experience and expertise so you 
should

feel comfortable with any question.
To the coax delay question. You are not pushing the limits.
But its important to understand the impacts of such long lines.
They need to be driven and terminated and the rise time will suffer from
the line capacitance. Essentially a fast rise time will become a slow
risetime on teh other end. There are lumped lc network delay lines. I have
experimented with them. They have the same effect. But you can cascade 
them

and use an inverter or buffer between each one.Each inverter also adds
delay. This helps the rise time issue. But the buffers add jitter and each
also adds delay thats temperature sensitive.
For cascaded delays of very short duration I have actually used 74LS244s
74HC244 line drivers cascaded and they work really well but only good for
each drivers delay.
Others will have better answers.
Regards
Paul
WB8TSL

On Tue, Nov 24, 2015 at 9:04 AM, Thomas Allgeier <th.allge...@gmail.com>
wrote:


Hello,



I have an ACAM GP22 TDC chip and evaluation board which I am looking at
for “work” purposes – I work for a company active in the weighing and 
force

measurement world.



I should say from the start that I am new to time and frequency
measurements and not even an electronics engineer – but then I have been
exposed to high-precision electronics for the last 25 years hence have
picked up some dangerous degree of half-knowledge.



We want to use this chip to measure the period of a square wave, of 
around

13 kHz i.e. in the 70 µs range. As the application is potentially
high-accuracy we need to know the period to within 1 ns or better.



In order to evaluate the chip I was planning to replicate John A’s
experiment with the coaxial delay line from the HP5370b – but as my
interest is in “measuring range 2” of the GP22 I need a delay of 500 ns 
or
more (actually 1 µs sounds a better start). This is the equivalent of a 
200

m length of cable. I fear trouble with this: Am I not getting unwanted
inductivities if I use a coil of that size?



So, to come to the point: Am I pushing the concept of a coax delay too 
far

with 1 µs and are there other (simple/reliable) ways to achieve this kind
of delay? I have tried it with a shorter piece of cable (around 2 ns 
which

is measured in “range 1”), there I seem to get consistency virtually to
within 100 ps. But I need to know if the device sticks to this level of
performance when the periods are much longer, and thus measured in “range
2”.



Thanks and best regards,

Thomas.
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Re: [time-nuts] ACAM GP22 Chip

[Thomas Allgeier]

Hello Bob,

Thanks for the suggestions - these sound a bit beyond my current level of 
skills and kit. But I do have people to call on in the office who may be 
able to rig something like that up for me should the coax route fail.


Best regards,
Thomas.
- Original Message - 
From: "Robert LaJeunesse" <lajeune...@mail.com>

To: <time-nuts@febo.com>
Sent: Tuesday, November 24, 2015 6:25 PM
Subject: Re: [time-nuts] ACAM GP22 Chip


If the goal is to create two signals consistently spaced near 70us apart 
why not use a good, fast 8-bit serial-in, parallel out shift register, 
clocked cleanly at 100kHz? Using the outputs from stages 1 and 8 would 
result in a 70us delay between signals. The data in would be fed 100KHz 
divided by 10 (or 16, or anything greater than 8) at whatever duty cycle 
is available. This allows the GP22 to see the combined instabilities of 
the clock and the shift register, which could be down in the nanosecond 
range, possibly less since the shift register delays would inherently 
cancel all but their differences.


Bob LaJeunesse


Sent: Tuesday, November 24, 2015 at 9:04 AM
From: "Thomas Allgeier" <th.allge...@gmail.com>
To: time-nuts@febo.com
Subject: [time-nuts] ACAM GP22 Chip

Hello,

I have an ACAM GP22 TDC chip and evaluation board which I am looking at 
for “work” purposes – I work for a company active in the weighing and 
force measurement world.


...

We want to use this chip to measure the period of a square wave, of 
around 13 kHz i.e. in the 70 µs range. As the application is potentially 
high-accuracy we need to know the period to within 1 ns or better.

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[time-nuts] ACAM GP22 Chip

[Thomas Allgeier]

Hello,



I have an ACAM GP22 TDC chip and evaluation board which I am looking at for 
“work” purposes – I work for a company active in the weighing and force 
measurement world.



I should say from the start that I am new to time and frequency measurements 
and not even an electronics engineer – but then I have been exposed to 
high-precision electronics for the last 25 years hence have picked up some 
dangerous degree of half-knowledge.



We want to use this chip to measure the period of a square wave, of around 13 
kHz i.e. in the 70 µs range. As the application is potentially high-accuracy we 
need to know the period to within 1 ns or better.



In order to evaluate the chip I was planning to replicate John A’s experiment 
with the coaxial delay line from the HP5370b – but as my interest is in 
“measuring range 2” of the GP22 I need a delay of 500 ns or more (actually 1 µs 
sounds a better start). This is the equivalent of a 200 m length of cable. I 
fear trouble with this: Am I not getting unwanted inductivities if I use a coil 
of that size?



So, to come to the point: Am I pushing the concept of a coax delay too far with 
1 µs and are there other (simple/reliable) ways to achieve this kind of delay? 
I have tried it with a shorter piece of cable (around 2 ns which is measured in 
“range 1”), there I seem to get consistency virtually to within 100 ps. But I 
need to know if the device sticks to this level of performance when the periods 
are much longer, and thus measured in “range 2”.



Thanks and best regards,

Thomas.
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