Hello all -
"People talk about good deals on Thunderbolts but I have
yet to see one. It seems peak Thunderbolt passed before I was
seriously looking."
I would suggest some more serious looking. This guy "TRIMBLE GPS
RECEIVER 10MHZ CLOCK THUNDERBOLT" currently has more than 10 T-bolts
for sale on eBay as of this morning for $ 175.
Last summer I bought 3 of his units and all were in great condition and
worked just fine. the one pictured and all of the ones I obtained had a
nice MiniCircuits 2 way splitter that came with it. The splitter is
about $ 50 new and usable at 10 MHz and over a wide bandwidth.
In fact during the several days of lamenting the lack of T bolts there
were several vendors offering them for various prices from good to not
so good.
As to building a GPS DO some of the recent comments from persons
dedicated to precision time and frequency - apparently willing to go to
extreme measure to achieve it seem curious to say the least. Here
performance seemed to be unspecified and of less importance than what
uP to use.
As usual there was the temptation to jump to implementations without
the steps essential to any
good design to wit:
1. A agreed to requirements document
2. A peer reviewed specification
3. A conceptual design and conceptual packaging concepts (What should
the box cost?)
4. A conceptual design review
5. A preliminary circuit design, SW design, and final package concept.
6. Implementation and test of the preliminary circuit and SW design.
7. Incorporation of the test results and final design release.
Instead the discussion has centered on what microprocessor (of a
hundred that would work)
and how to eliminate "glue" logic and and a few analog parts to save
money. This is silly - silicon is
CHEAP.
Major cost items not considered include - somewhat in order of
decreasing cost :
*The box you put it in - suspending it above the bench on inspirational
thought probably
will not work. A nice box is easily $ 50.00 so who cares about adding
another flip flop or
counter at 25 cents each.
*The printed wiring board. Most costly per unit up to about 4 pieces
* A power supply - you will need a good low noise one.
* OCXO
So when you look at the total system - any GPS DO when fully developed
and packaged into
a unit with long term reliability and performance acceptable to this
group is a non-trivial project. It is,
however a challenging and rewarding project - particularly if well done.
-73 john k6iql
-----Original Message-----
From: time-nuts-request <[email protected]>
To: time-nuts <[email protected]>
Sent: Sat, Dec 8, 2012 2:56 am
Subject: time-nuts Digest, Vol 101, Issue 63
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Today's Topics:
1. Re: GPSDO Alternatives - Bert's boards (WB6BNQ)
2. Re: PPS offset between GPS receivers (Chris Albertson)
3. Re: GPSDO Alternatives (David)
4. Re: PPS offset between GPS receivers (Bob Camp)
5. Re: Open source (Poul-Henning Kamp)
6. Re: Open source (David Kirkby)
7. Re: Termination talk (Attila Kinali)
----------------------------------------------------------------------
Message: 1
Date: Fri, 07 Dec 2012 18:06:17 -0800
From: WB6BNQ <[email protected]>
To: Discussion of precise time and frequency measurement
<[email protected]>, [email protected]
Subject: Re: [time-nuts] GPSDO Alternatives - Bert's boards
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii
Hello Bert,
The boards look nice but tell me nothing of the circuitry. How about
sending the schematics ?? That way I
can appreciate what it is that you have.
Bill....WB6BNQ
p.s. By the way, what ever happen with that DMTD you were going to
produce about three years ago ?
[email protected] wrote:
Attached is my latest ExpresPCB layout of a GPSDO. A clear
understanding
of the GPS limitations, a goal as to what I want to control ,focus on
attainability, reproducibility KISS, cost and tests of partials on
development
boards and what you see if you download the ExpessPCB software is on
the
right the saw tooth correction, in the middle the analog board with
opto
isolation to prevent ground loop and on the right the actual GPSDO.
This
particular unit also allows you to link a 20 Hz offset FRS-C (part of
my dual
mixer) to my house reference. Total material cost depending how many
boards one
buys is below $ 40. I will include this particular board along with
other
designs on my next order and subsequently cut with a sheer.
The board on the right could be used by itself with minor
modifications to
directly drive a FE 5680 if some one would step up to the task.
Total cost
below $ 15. I use the analog board, which by the way is the most
expensive
since it has a LTC 1655 and REF 02.
No dither 16 bits, dither 18 bits and depending on loop time, clock
frequency range starting at 3 E-9 and resolution up to 6 E-16.
Again I am only interested in to controlling a Rb which gives me way
more
flexibility, the Rb's are either modified with a 10811 or in one
case with
the M1000 and in the case of the FE 5680 a MV89 with a separate
analog loop.
And in all cases the RB is temperature controlled.
All this based on over 10 years of work with the Shera controller,
exclusively controlling Rb's.
Bert Kehren
One more thought you may want to look at a 1 $ gate array for all
your
timing issues. Simplifies the work dramatically. With the long loop
times
associated with Rb and high sample rate, 100 psec. are no problem.
------------------------------------------------------------------------
Name: Shera 3 board.pcb
Shera 3 board.pcb Type: PCB Wizard Document
(application/x-unknown-content-type-PCBWizard.Document)
Encoding: base64
------------------------------------------------------------------------
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------------------------------
Message: 2
Date: Fri, 7 Dec 2012 18:19:58 -0800
From: Chris Albertson <[email protected]>
To: Discussion of precise time and frequency measurement
<[email protected]>
Subject: Re: [time-nuts] PPS offset between GPS receivers
Message-ID:
<CABbxVHurvqYoZnMv=+jt6bq4i6aw+jefgrmldmkm7ruv1dm...@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
One more test to try. Connect one PPS signal to both GPIO ports and see
how close to zero offset you get. It would likely be random which gets
read first.
On Wed, Dec 5, 2012 at 5:37 AM, Gabs Ricalde <[email protected]>
wrote:
Hi everyone,
As Tom suggested, I redid the test with less than 1 ft. of wire from
the
PPS output to the GPIO without any logic gates or line receivers. Same
result,
the SKG25A1 was 2 microseconds ahead of the 58534A. Without any other
way
of
testing, I would probably trust the output of the timing receiver more
than the SkyNav module. Anyway the SkyNav board is an inexpensive
unit and
I wouldn't mind setting an offset in ntpd.
I don't have a scope yet, and a low jitter PPS GPIO is the closest
thing I
have
to a TIC.
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--
Chris Albertson
Redondo Beach, California
------------------------------
Message: 3
Date: Fri, 07 Dec 2012 20:38:52 -0600
From: David <[email protected]>
To: Discussion of precise time and frequency measurement
<[email protected]>
Subject: Re: [time-nuts] GPSDO Alternatives
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii
On Fri, 07 Dec 2012 17:50:55 -0500, "Charles P. Steinmetz"
<[email protected]> wrote:
John wrote:
What's *really* interesting, though, is the idea that collectively
we might develop some standard measurement protocols that would be
reproducible in a number of (amateur) labs.
I agree, but I didn't dare to dream so large when I wrote:
From my perspective, the most interesting development would be an
offer
by someone with a very well equipped lab to test any DIY GPSDO with a
consistent protocol and publish the results. That way, we could all
see
how the various approaches compare with respect to the
characteristics
that are most important to each of us.
At bottom, any such testing requires (i) a comparison standard at
least as good (and hopefully at least somewhat better) than the DUT
at all taus and offsets (which may, in reality, be several standards,
each doing part of that job), (ii) a reliable TIC (and, potentially
usefully, frequency counter) that can exploit the stability of the
comparison standard, and (iii) the capability to process the raw data
to produce meaningful information. [Additionally, to characterize
poor-signal behavior one would presumably use attenuators and a
well-situated antenna. Some may not have good antenna sites to begin
with, and in any case, it would be hard to standardize the signal
strength between locations.]
My thoughts were (1) for many (most?) of the people who would want to
build a DIY GPSDO, it would likely be their first "really good"
standard, and therefore their best; and (2) the range of
TICs/frequency counters owned by the target base is so wide, and
covers such a large range of capabilities (to say nothing of whether
any given counter is in good repair and being used to best
advantage), that obtaining comparable results from one amateur lab to
another would be just as much if not more dependent on the individual
counters involved than on the GPSDOs under test.
However, that is no reason not to push forward with standardized
measurement protocols, which would focus all of us on what the
relevant desiderata are and how to measure them.
For myself:
1. My current lack a comparison standard is the reason I would design
and build a GPSDO. At best I might buy a used rubidium oscillator at
some point. People talk about good deals on Thunderbolts but I have
yet to see one. It seems peak Thunderbolt passed before I was
seriously looking.
2. So far my best universal counter is a rebuilt Racal Dana 1992 with
a TCXO but it lacks GPIB. It might be easier and cheaper for me to
duplicate my GPSDO phase detector and add a counter chain and trigger
so it can make and report its own time interval measurements against a
secondary asynchronous source but that would hardly be reproducible by
a third party.
3. I am less interested in this since I will be at the mercy of
whatever timing GPS I use and my current antenna environment.
------------------------------
Message: 4
Date: Fri, 7 Dec 2012 22:28:20 -0500
From: Bob Camp <[email protected]>
To: Discussion of precise time and frequency measurement
<[email protected]>
Subject: Re: [time-nuts] PPS offset between GPS receivers
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii
Hi
A lot depends on exactly what the interrupt structure is. It may also
depend on the phase of the cpu clock relative to the pps signal. What's
reasonably sure is that there is indeed some offset between the two
where the answer is indeed "ft's" random. Another thing to check - how
wide is the random region?
Bob
On Dec 7, 2012, at 9:19 PM, Chris Albertson <[email protected]>
wrote:
One more test to try. Connect one PPS signal to both GPIO ports and
see
how close to zero offset you get. It would likely be random which
gets
read first.
On Wed, Dec 5, 2012 at 5:37 AM, Gabs Ricalde <[email protected]>
wrote:
Hi everyone,
As Tom suggested, I redid the test with less than 1 ft. of wire from
the
PPS output to the GPIO without any logic gates or line receivers.
Same
result,
the SKG25A1 was 2 microseconds ahead of the 58534A. Without any
other way
of
testing, I would probably trust the output of the timing receiver
more
than the SkyNav module. Anyway the SkyNav board is an inexpensive
unit and
I wouldn't mind setting an offset in ntpd.
I don't have a scope yet, and a low jitter PPS GPIO is the closest
thing I
have
to a TIC.
_______________________________________________
time-nuts mailing list -- [email protected]
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
--
Chris Albertson
Redondo Beach, California
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------------------------------
Message: 5
Date: Sat, 08 Dec 2012 08:36:08 +0000
From: "Poul-Henning Kamp" <[email protected]>
To: Discussion of precise time and frequency measurement
<[email protected]>, Chris Albertson <[email protected]>
Subject: Re: [time-nuts] Open source
Message-ID: <[email protected]>
--------
In message
<cabbxvhujtsd4btdq7dbm88-gfuv9kbesr5_jovaeubvrjnc...@mail.gmail.com>,
Chris Albertson writes:
Many authors ike GPL because they figure "I wrote this and I'm giving
this
away for free, I don't want some other guy to take it, change the
title and
claim it as his own work and charge money for it."
BSD on the other hand allows it The University of Califoornia used
BSD
because their goal was to get the technology out into the world and
allowing someone to make money is a good way to do that.
The BSD license does not allow you to "claim it is yours", in fact,
no license is needed to preserve that right, as the Berne Convention
and all copyright laws I know about, protects the "creators ideal
rights" (= the right to be known as the creator) by default.
In practice there are a few other wrinkles between GPL and BSD.
In particular the GPL code can "taint" your own code if you get them
too close together, so that you can be forced to release your own
code as GPL, simply by using a GPL submodule. (This is why some
license-fanatics call the GPL "a viral license")
And one other detail most people overlook, is that the default GPL text
gives any users the right to use any later version of the GPL license
instead of the one you copy&pasted. This has only happened once but
it had ground-shaking repercussions through out the industry.
As for the economy, as an open source author, my experience is that
there is more money to be made with the BSD license than with the
GPL license, simply because the companies which might be willing
to pay, also like the extra freedom of the BSD license.
And as was said, there is a ton of other OSS-licenses out there,
you can see a sort of a list here:
http://opensource.org/licenses/index.html
my own contribution to the area, was used on a piece of code I
wrote, which during its most popular use-period, protected upwards
of 50% of all passwords on the internet:
http://en.wikipedia.org/wiki/Beerware
--
Poul-Henning Kamp | UNIX since Zilog Zeus 3.20
[email protected] | TCP/IP since RFC 956
FreeBSD committer | BSD since 4.3-tahoe
Never attribute to malice what can adequately be explained by
incompetence.
------------------------------
Message: 6
Date: Sat, 8 Dec 2012 08:44:21 +0000
From: David Kirkby <[email protected]>
To: Discussion of precise time and frequency measurement
<[email protected]>
Subject: Re: [time-nuts] Open source
Message-ID:
<CANX10hC+=aSGLiGvwXnXYQuDUzGu2wbrzNXiGgogKcFrKPr=p...@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
On 8 December 2012 01:09, Chris Albertson <[email protected]>
wrote:
BTW you CAN make as much money as you like with GPL'd software. Just
look
at all Android phones. They contain Linux and a pile of other GPL'd
software. Apple is using BSD Unix in there products.
That's an important point, and something the person that wrote the
GPSDO software might like to consider.
You don't need to be the size of Apple to make money from GPL. Plenty
of people earn money from providing support for GPL software. There
are numerous consultants for R (statistics package), Apache (web
server), Wireshark (network analysis) etc. I've made money by selling
support for a GPL program I wrote.
http://atlc.sourceforge.net/
with hindsight, I could have probably made more, as a commerical
company contacted me, asking if I could license it under the LGPL so
they could use it in their closed-source commerical software. I
refused. But with hindsight, I could have sold them a license to use
it in their closed source application.
As a company, if you use GPL software, you are not tied to one vendor.
If there is a feature you want, you can eitiher add it yourself, ask
the original author to add it, or if need be pay someone else to add
it.
Dave
------------------------------
Message: 7
Date: Sat, 8 Dec 2012 09:55:20 +0100
From: Attila Kinali <[email protected]>
To: Discussion of precise time and frequency measurement
<[email protected]>
Subject: Re: [time-nuts] Termination talk
Message-ID: <[email protected]>
Content-Type: text/plain; charset=US-ASCII
On Fri, 07 Dec 2012 23:42:44 +0100
Magnus Danielson <[email protected]> wrote:
Only then he
made the comment that there might be something in that "Black Magic"
book that I had bought and distributed.
Which book would that be?
Attila Kinali
--
There is no secret ingredient
-- Po, Kung Fu Panda
------------------------------
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