Delay through GPS antenna splitter/amplifier -- an answer, and a question
On Mon, 12 Mar 2007 17:16:49 -0400, "Mike Feher" mfeher@eozinc.com
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 bring up a more common hobby that soaks
up lots of time, effort and money, like car racing. Most people are
already calibrated to accept that one, even though it serves no useful
purpose. My hobby is just like that, only different.
Dr Bruce Griffiths bruce.griffiths@xtra.co.nz 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 cable delays (including the antenna to splitter cable) should also
be a multiple of half the signal period to minimise the effects of
residual mismatches at either end of the cable.
Signal period? Periodic signals?
If only we had the luxury!
I was not working on the side of the lab where the experiments were
vaporized, though :-).
Tim.
Tim Shoppa wrote:
Dr Bruce Griffiths bruce.griffiths@xtra.co.nz 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 cable delays (including the antenna to splitter cable) should also
be a multiple of half the signal period to minimise the effects of
residual mismatches at either end of the cable.
Signal period? Periodic signals?
If only we had the luxury!
I was not working on the side of the lab where the experiments were
vaporized, though :-).
Tim.
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Tim
Sorry I should have said a multiple of half the L1 carrier period
(~634.75 ps).
So the cable delay should be a multiple of 317.375...ps.
Bruce
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 Ackermann N8UR jra@febo.com wrote:
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 antenna
port to output port is around 15 nanoseconds for the
eight way unit, and
about 22 nanoseconds for the two way one. The delay
seems consistent on
all the ports, with less than 1 nanosecond
variation.
However, there is also a hump in the delay near the
edges of the
passband, about 12 MHz above and below the center.
The delay at the
edges increases by perhaps 5 nanoseconds, though
depending on the port,
it's not always symmetrical.
So, an interesting question for any of you real
GPS experts is what
effect a variation in group delay of the RF input
has on the timing
solution? Is the true "length" of the amp/splitter
some average of the
delay across the passband, or, given the spread
spectrum nature of the
signal, does it not really matter? In fact, is the
"length" of the
splitter even related to the measured group delay?
This also raises the issue that any GPS antenna that
has RF filtering is
likely to have similar delays; I've never seen that
sort of data published.
John
time-nuts mailing list
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Get your own web address.
Have a HUGE year through Yahoo! Small Business.
http://smallbusiness.yahoo.com/domains/?p=BESTDEAL
Now that is obsessive!!
:-))
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Dr Bruce Griffiths
Sent: 12 March 2007 22:39
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Delay through GPS antenna splitter/amplifier -- an
answer, and a question
Tim Shoppa wrote:
John Ackermann N8UR jra@febo.com 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 up six matched cables to go from the
splitter to the receivers -- they all test within about 1 nanosecond of
each other.
Obsessive compulsive? Me?
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 :-).
Tim.
time-nuts mailing list
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John
Your not quite obsessive enough.
The cable delays (including the antenna to splitter cable) should also be a
multiple of half the signal period to minimise the effects of residual
mismatches at either end of the cable.
Bruce
time-nuts mailing list
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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?"
"For the money, for the glory, and for the fun. But mostly for the
fun..."
(with apologies to Burt Reynolds)
Tom Frank, KA2CDK
On Tue, 13 Mar 2007 20:31:31 -0400, Thomas A. Frank ka2cdk@cox.net
wrote:
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?"
"For the money, for the glory, and for the fun. But mostly for the
fun..."
(with apologies to Burt Reynolds)
I'm not at the cesium level of time-nut insanity yet but I have other
nerdy vices. When people ask me why, my usual answer is "for the same
reason I have sex. I can and it feels good". I get funny looks
sometimes.......
John
John De Armond
See my website for my current email address
http://www.neon-john.com
Cleveland, Occupied TN
Don't let your schooling interfere with your education-Mark Twain
I suppose an answer could be "Time will tell"
It's better than "Because I can"
-----Original Message-----
From: time-nuts-bounces@febo.com [mailto:time-nuts-bounces@febo.com] On
Behalf Of Thomas A. Frank
Sent: Tuesday, March 13, 2007 7:32 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Delay through GPS antenna splitter/amplifier
--ananswer, and a question
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?"
"For the money, for the glory, and for the fun. But mostly for the
fun..."
(with apologies to Burt Reynolds)
Tom Frank, KA2CDK
time-nuts mailing list
time-nuts@febo.com
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
This brings the following story back in my mind:
When I was a student at the university of Bochum/Germany the department
of physics owned an electron synchrotron and storage ring. Not really a
big gun in international terms but with 800 MeV energy also not exactly
a child's toy. Once a year the university had its "open day" when the
public was invited to visit the numrerous research facilities.
There was this old lady who had listened to the lecture that the
scientist responsible for the accelerator had given. Although the
lecture had clearly been public-adressed she had hardly understood a bit
of what it all was about. After the lecture, when the other vistors had
already left the laboratory, she talked to the scientist: "Sir, thank
you for your highly interesting lecture. Its just that I missed one
thing: What do you need it for?"
The scientist, anticipating that explaining it to the old lady might be
a task of hours or perhaps impossible, answered: "Mam, it is kind of a
hobby of mine. You know, other men own model railways and watch the
small trains running in circles. What I do is pretty much the same only
with electrons and at a bit more speed". The old lady went away
completely satisfied because now she had really understood....
Cheers
Ulrich Bangert, DF6JB
-----Ursprüngliche Nachricht-----
Von: time-nuts-bounces@febo.com
[mailto:time-nuts-bounces@febo.com] Im Auftrag von MUELLER,
STEVE (ATTOPS)
Gesendet: Mittwoch, 14. März 2007 18:57
An: Discussion of precise time and frequency measurement
Betreff: Re: [time-nuts] Delay through GPS antenna
splitter/amplifier--ananswer, and a question
I suppose an answer could be "Time will tell"
It's better than "Because I can"
-----Original Message-----
From: time-nuts-bounces@febo.com
[mailto:time-nuts-bounces@febo.com] On Behalf > Of Thomas A.
Frank
Sent: Tuesday, March 13, 2007 7:32 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] Delay through GPS antenna
splitter/amplifier --ananswer, and a question
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?"
"For the money, for the glory, and for the fun. But mostly for the
fun..."
(with apologies to Burt Reynolds)
Tom Frank, KA2CDK
time-nuts mailing list
time-nuts@febo.com
https://www.febo.com/cgi-> bin/mailman/listinfo/time-nuts
time-nuts mailing list
time-nuts@febo.com
https://www.febo.com/cgi-> bin/mailman/listinfo/time-nuts
The local surplus guy got in a few dozen coax switches. The only markings on
them say "Type DSWA0". Dimensions are about 2.6" H x 2" D x 1" W. There is a
toggle switch on the front and three BNC connectors on the back.
I can't find any information about these. Does anyone know anything about
these?
Thanks.