Hi Said,
Late reply... (been busy)
The purpose of the straight drive is to maximize the signal amplitude on
the cable. The test intends to demonstrate that it is perfectly adequate if
only the far end is matched, and yet you get twice the amplitude you would
get with a 50 ohm drive signal.
On
It's the rise-time that kills you.
You can under certain circumstances avoid termination, and gain better
amplitude, but you then need to make sure that the reflections is not
going to disturb your measurements.
The general recommendation is to do proper termination. If you know the
signal
Hi Tom,
This page will show you the kind of problems to expect:
http://ko4bb.com/Test_Equipment/CoaxCableMatching.php
Didier KO4BB
On September 15, 2014 8:43:21 AM CDT, Tom Van Baak t...@leapsecond.com wrote:
How important are all these cable / termination / impedance issues for
1PPS signals?
Hi Didier,
You showed the effect of standard end-termination and no end-termination both
while driving the cable with a mis-matched low signal source impedance. These
are the same type of plots that Tom posted a link to last week.
The interesting plots will be when you set R1 to match the
Hi Hal,
I think its a slow driver, and a complex output impedance, not necessarily a
weak driver.
I have a Tbolt hidden somewhere and would need to dig it out. My 30 foot cable
disappeared though, so I need to buy a new one :(
On the small hump, i don't think that is a reflection. The signal
saidj...@aol.com said:
here are some plots from two GPSDOs, one series terminated (CSAC GPSDO),
and one load-terminated (Agilent 58503A) product.
Nice pictures. Thanks.
My reading of your pictures is that the 58503A has a weak driver. Do you
have a TBolt?
... and there is a little hump
How important are all these cable / termination / impedance issues for 1PPS
signals? I know ringing and reflections are undesirable in many applications.
But for 1PPS?
I often use pick whatever cable, termination, and trigger level gives the
cleanest edge, the best risetime. What happens to
Fast risetime pulses _are_ RF and need to be treated as such.
Tom
- Original Message -
From: Tom Van Baak t...@leapsecond.com
To: Discussion of precise time and frequency measurement
time-nuts@febo.com
Sent: Monday, September 15, 2014 9:43 AM
Subject: Re: [time-nuts] Correcting
Some good refs on coax driving showing scope traces for ringing etc:
http://www.ti.com/lit/an/snla043/snla043.pdf
http://www.ti.com/lit/an/sboa075/sboa075.pdf
On Mon, Sep 15, 2014 at 9:43 AM, Tom Van Baak t...@leapsecond.com wrote:
How important are all these cable / termination / impedance
On 9/15/2014 10:01 AM, Tom Miller wrote:
Fast risetime pulses _are_ RF and need to be treated as such.
You say that as if simply saying it provides an explanation, or even a
reason. Exactly what ill effect on a triggered measurement is there if
one does not terminate a PPS signal properly?
Hi guys,
Tried to bring my point across, but I guess I failed to do so properly.
What happens after the edge is very important because what happens after the
edge settles is up to 100mA DC current is flowing through all the coaxes AND
your building ground.
Pumping ~5V into 50 Ohms
Looks like this email did not make it:
Hi guys,
Tried to bring my point across, but I guess I failed to do so properly.
What happens after the edge is very important because what happens after
the edge settles is up to 100mA DC current is flowing through all the coaxes
AND your
I found the schematics of the Mini-T output circuit. It actually is a
single 10 Ohms series resistor (R32) driven by six parallel 74AC04 gates.
Thus only a single resistor change on the Mini-T would fix the issue. Since
the gates probably have about 2 Ohms equivalent impedance, simply
I don't claim to be able to do the math, but one could probably easily
calculate it from the Fourier frequencies by looking at the attenuation by
frequency over a 1km lengh:
Loss per 100m over frequency:
10M100M400M1300M2300M
7dB14dB28dB 49dB72dB
So
Also, another issue with the end termination happens when driving very long
coax cables: RG-142 for example has about 60 Ohms center conductor
resistance and 7.5 Ohms shield resistance at 1km length.
RG-142 is far from low-loss. Does anybody use it at that length?
What's the rise time
been shown necessary
to make precise measurements (something this group strives for).
YMMV,
Tom
- Original Message -
From: Mike S mi...@flatsurface.com
To: time-nuts@febo.com
Sent: Monday, September 15, 2014 10:29 AM
Subject: Re: [time-nuts] Correcting jitter on the 1
On 9/15/2014 3:04 PM, Tom Miller wrote:
So does adding ~80 pF per meter or 8 nF for 100 meters (RG58) to your
output have any effect on the risetime? Because that is what it will see
with an open cable.
It's not nearly that simple. 8 nF distributed along 100 M is not the
same as an 8 nF cap
tmiller11...@verizon.net said:
So does adding ~80 pF per meter or 8 nF for 100 meters (RG58) to your output
have any effect on the risetime? Because that is what it will see with an
open cable.
That way of thinking only works if the risetime is long relative to the cable
length. In this
They say that the system clock is 12.504 MHz and that they use both the
rising and falling edges. That is about 40 nS between quantization time
slots. The PPS can only appear on a 40 nS edge. I should be seeing
40 nS jumps in the waveforms. I do see ~40 nS jumps but they are less
Hi
Actually your “best case” is where the clock in the Res-T is *not*
12.504000 MHz or a frequency that is +/- (N * 40 ppb) of that
frequency. If it is, you get a “hanging bridge” in the data. At +/- (N * 20
ppb) you don’t get the classic hanging bridge, but you still get a bias. All
20 matches
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