I had a chance recently to look at the performance of the two-port and
eight-port HP GPS antenna splitters on a super-duper network analyzer.
Screenshots of the results are at
http://www.febo.com/time-freq/pages/gps-splitter.
In short, the minimum delay (at the center of the passband) from
From my experience, your position and hence derived time is based on the
antenna centre. Cable, splitter, connector, and antenna filter delays all
need to be taken into account when looking at very accurate nanosecond
timing applications.
For most applications in the microsecond or tens of
But we're time-nuts... we DO worry about those things. :-)
While we were at it with the network analyzer, we did FDR (frequency
domain reflectometry) to measure the cable delay to the antenna, and I
spent yesterday making up six matched cables to go from the splitter to
the receivers -- they
In message: [EMAIL PROTECTED]
Rob Kimberley [EMAIL PROTECTED] writes:
: From my experience, your position and hence derived time is based on the
: antenna centre. Cable, splitter, connector, and antenna filter delays all
: need to be taken into account when looking at very accurate
So, what's it take to make a Cell Phone Disciplined Oscillator?
I've seen some timing products based on CDMA cell systems, but haven't
seen any that use an actual cell phone.
An old (older=better) CDMA phone can be made to work as an experimental
platform, but the whole thing is not trivial.
From: John Ackermann N8UR [EMAIL PROTECTED]
Subject: [time-nuts] Delay through GPS antenna splitter/amplifier -- an answer,
and a question
Date: Mon, 12 Mar 2007 11:03:12 -0400
Message-ID: [EMAIL PROTECTED]
John,
I had a chance recently to look at the performance of the two-port and
I had a chance recently to look at the performance of the two-port and
eight-port HP GPS antenna splitters on a super-duper network analyzer.
Screenshots of the results are at
http://www.febo.com/time-freq/pages/gps-splitter.
Super nice plots, John.
Tom Clark, do you have comments?
John,
From: John Ackermann N8UR [EMAIL PROTECTED]
Subject: Re: [time-nuts] Delay through GPS antenna splitter/amplifier -- an
answer, and a question
Date: Mon, 12 Mar 2007 12:04:06 -0400
Message-ID: [EMAIL PROTECTED]
But we're time-nuts... we DO worry about those things. :-)
Indeed!
Oh my goodness,
Tom Van Baak wrote:
John, next time you can borrow that instrument blow
some hot/cool air on the antenna and see what changes
and by how much.
I've heard that the older GPS antennas, the ones with zero
or less RF filtering, were much better for timing applications
but have never seen data
Magnus Danielson wrote:
I would use TDR/TDT for that. :)
My buddy the expert tells me that using frequency sweep rather than
pulse techniques is preferred these days. With multi-GHz sweeps, you
can get better resolution, and you also minimize the problems that
strong external signals can
From: John Ackermann N8UR [EMAIL PROTECTED]
Subject: Re: [time-nuts] Delay through GPS antenna splitter/amplifier -- an
answer, and a question
Date: Mon, 12 Mar 2007 13:17:50 -0400
Message-ID: [EMAIL PROTECTED]
Magnus Danielson wrote:
I would use TDR/TDT for that. :)
My buddy the expert
I used to be bothered when I was working on this stuff full time, especially
when we were testing equipment in labs for customers on a mission. Now, as
long as all my clocks are on the same second.
:-)
Funny story however.. Was at NPL on Thursday for our bi-annual Time
Frequency Club
In short, yes. If you want true traceability to NIST, you need to take
into account UTC(GPS) versus UTC(NIST).
And it gets uglier yet. If you want UTC you have to take
into account the UTC - UTC(NIST) delta, which was about
16 ns in January. See the full 2006 record:
Just a swag, it's probably reasonable to assume that each stage of
filtering adds about 10ns of delay.
That should be reasonable to measure.
Setup a system without the splitter/filter/whatever, and use that to
calibrate a local reference clock. Then insert the unit you want to test and
When you get to the sub-100 ns level UTC is not GPS. And
UTC(NIST) isn't UTC(USNO). Even the national labs don't
agree down to the last ns.
/tvb
Remember that no one lab has the true UTC clock. UTC is an offset to Atomic
Time (TAI), and TAI is the weighted average of hundreds of clocks in
UTC-GPS is based on UTC-USNO, and therefore there will be a small offset
between other establishments like NIST, NPL who contribute to the UTC.
As you say, the offset will vary with time, so post-processing is the answer
in critical applications (which is the way UTC is determined anyway).
Rob
Funny story however.. Was at NPL on Thursday for our bi-annual Time
Frequency Club meeting. There was a small exhibition running and one of the
...
Rob,
That's a great story. And then this is how I was humbled...
I've had a few people over to my time lab and most are really
impressed. But I
From: Tom Van Baak [EMAIL PROTECTED]
Subject: Re: [time-nuts] Delay through GPS antenna splitter/amplifier --
ananswer, and a question
Date: Mon, 12 Mar 2007 10:46:40 -0700
Message-ID: [EMAIL PROTECTED]
Tom and Rob,
I often estimate time/distance relationships using simple rule-of-thumb
In message: [EMAIL PROTECTED]
Magnus Danielson [EMAIL PROTECTED] writes:
: Oh my goodness, the PPS is 10 ps late due to unmatched cable-lag! What should
I
: do? (For the egg-clock in the kitchen)
Put a tiny kink in the cable. That should be good for an offset of
that magnitude.
Magnus Danielson wrote:
From: Tom Van Baak [EMAIL PROTECTED]
Subject: Re: [time-nuts] Delay through GPS antenna splitter/amplifier --
ananswer, and a question
Date: Mon, 12 Mar 2007 10:46:40 -0700
Message-ID: [EMAIL PROTECTED]
Tom and Rob,
I often estimate time/distance relationships
is that a really tiny or maybe a medium tiny or are we talking a pico kink
(which is also smaller than a nano kink)???
i needed a smile for today as my time is up.
tom [EMAIL PROTECTED]
___
time-nuts mailing list
time-nuts@febo.com
This is the basic problem with our hobby... I proudly tell people that I
can measure time to trillionths of a second, but am hard pressed for a
good answer when they ask why do you need to?
I find myself giving the deer-staring-into-headlights look when people ask
me that same question!
In message: [EMAIL PROTECTED]
Jason Rabel [EMAIL PROTECTED] writes:
: This is the basic problem with our hobby... I proudly tell people that I
: can measure time to trillionths of a second, but am hard pressed for a
: good answer when they ask why do you need to?
:
: I find myself
M. Warner Losh said the following on 03/12/2007 02:52 PM:
In message: [EMAIL PROTECTED]
Jason Rabel [EMAIL PROTECTED] writes:
: This is the basic problem with our hobby... I proudly tell people that I
: can measure time to trillionths of a second, but am hard pressed for a
:
Sounds like Heisenberg :). -
Mike B. Feher, N4FS
89 Arnold Blvd.
Howell, NJ, 07731
732-886-5960
-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On
Behalf Of John Ackermann N8UR
Sent: Monday, March 12, 2007 3:06 PM
To: Discussion of precise time and frequency
Tim Shoppa wrote:
John Ackermann N8UR [EMAIL PROTECTED] wrote:
But we're time-nuts... we DO worry about those things. :-)
While we were at it with the network analyzer, we did FDR (frequency
domain reflectometry) to measure the cable delay to the antenna, and I
spent yesterday making
This is, incidentally, why isolators should be used on these runs.
This does create a problem with LNAs that are DC powered via coax, however
the reality is that many antennas and receivers do not have that great a
match to the coax impedance and could benefit from the clean up of an
isolator.
I just put a Z3801A on Ebay. This is a Z3801A without an antenna or
power supply
It is a clean unit and powers up and locks on to the satellites
The computer port has options set to RS232. The item no. is 190092049523
Thanks
Bill K7NOM
___
On Mon, 12 Mar 2007 17:16:49 -0400, Mike Feher [EMAIL PROTECTED]
wrote:
Sounds like Heisenberg :). -
Exactly! I was thinking, Why? Because it is there, to this current
degree of certainty.
When people are non-plussed by why I would spend time and money on one
of my uncommon hobbies, I try to
Dr Bruce Griffiths [EMAIL PROTECTED] wrote:
At the lab I worked at in the 80's, all the cables hanging on
the wall-racks were calibrated and labeled in nanoseconds.
But... after the ECL signals got turned into TTL, we just didn't
care anymore :-).
Your not quite obsessive enough.
The
Tim Shoppa wrote:
Dr Bruce Griffiths [EMAIL PROTECTED] wrote:
At the lab I worked at in the 80's, all the cables hanging on
the wall-racks were calibrated and labeled in nanoseconds.
But... after the ECL signals got turned into TTL, we just didn't
care anymore :-).
Your not
So the cable delay should be a multiple of 317.375...ps.
What's the thermal coefficient of coax?
--
These are my opinions, not necessarily my employer's. I hate spam.
___
time-nuts mailing list
time-nuts@febo.com
One is much better to take the filter's delay in
account rather than NOT USING a filter!!! i can hardly
imagine a GPS receiver/antenna without any form of
preselection, and, unfortunately, they're many of
those filterless units on the market!
73 de Normand VE2UM
Montreal, Qc. Canada
--- John
So the cable delay should be a multiple of 317.375...ps.
What's the thermal coefficient of coax?
Typically around 50-100ppm/C depending on the coax.
High velocity cables have lower tempcos
Handwaving...
100 ft of cable is 70ns or 7ps.
100ppm is 7ps.
10C is 70ps.
So if you start out
Hal Murray wrote:
So the cable delay should be a multiple of 317.375...ps.
What's the thermal coefficient of coax?
Typically around 50-100ppm/C depending on the coax.
High velocity cables have lower tempcos
Handwaving...
100 ft of cable is 70ns or 7ps.
100ppm
35 matches
Mail list logo
