A lot of devices have a low output impedance so that the signal can be split
using a TEE adapter with little loss or need for a distribution amplifier.
However, the cables must be impedance matched at far end, scope input, to
prevent reflections which are the source of the ringing.
You can
Is there any reason (other than cost) not to both series-terminate the
source and parallel-terminate the sink?
When I was dealing with analog video, the standard distribution method was :
1. Buffer amplifier with high input impedance, very low output
impedance, and a gain of 2 (so 1 V P-P
Hi the list,
Just wanted to introduce myself for my 1st message.
I'm Stephane, 40, living in France, at the moment working in RF
electronics for a particles accelerator lab. I'm hamradio as well, and I
do enjoy especially weak and accurate signals.
I'm desiging various RF circuits. Current
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?
You need not have a properly terminated transmission line but you
must then worry about the bounce. If you understand the size
of the bounce and have a system that will not suffer false triggering
then you will be OK.
There are some worries however. It is hard to predict the exact
size of
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
Hi Stephanie,
Welcome to the list!
We designed a 1GHz crystal LO for PLLs (the ULN-1G) using an off the shelf
miniature 500MHz crystal oscillator which is run at 3 rd overtone internally
then using a diode doubler and a steep bandpass filter using several Mini
Circuits ceramic filters and a
My daughter and I were discussing what she does for a living with time and
phase as a geophysicist and relating that to what I'm trying to do with my
GPSDOengine. I explained that I was trying to keep the frequency accurate and
stable, while also keeping the phase near a target of 180 degrees.
Hello Said,
Thanks for the answer.
Sounds interresting. Do you have a description of that ? Especially a
phase noise plot ?
As said, I'm planning to use a VCXO (low cost and low noise) at 100 MHz
followed by a MMIC (ERA) and a 500 MHz 3-cells helical filter from
Temwell. Then a doubler
Hi,
It sounds like all my messages need moderator approbation. Is it the
rule on the list or a technical problem at my side ?
Cheers
Stephane
On Mon, 15 Sep 2014 09:17:01 -0700, Said Jackson via time-nuts
time-nuts@febo.com wrote:
Hi Stephanie,
Welcome to the list!
We designed a 1GHz
Hi Stephanie,
I have a similar issue, I can never tell if my messages post or not, some I
get back instantly others never show up in my inbox. I think the mail
server was just updated..
To answer your questions:
1) attached is the PN plot of the 1.0GHz version.
2) Here is a datasheet
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
Hi Dave,
yes there is a reason.
The standard 1PPS signal termination (Thunderbolt etc) used to be 5 Ohms
or less series termination into a 50 Ohms coax (yikes), then end-terminate
to get rid of all the undesired reflections.
Your example below is properly terminating a 75 Ohms coax with
Hi Stephane,
Welcome. There's nothing wrong on your end. Thanks for asking.
Subscription to this list is open to all without approval. Since about a year
or two ago postings from new subscribers are moderated. Any technically rich,
on-topic posting goes through.
/tvb (i5s)
On Sep 15, 2014,
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 will agree that the end termination is optional if you are delivering a
pulse signal to just one input, which is at the far end of the coax.
However, I think there's still a problem with series-only termination when
the pulse signal is daisy-chained through multiple inputs. When you apply
5
Hi Dave,
what you are describing is reflected wave switching, which works perfectly
in applications such as the PCI bus. The PCI bus uses it because it lends
itself to extremely low power consumption.
Your scenario does not work with end-termination either if you have
multiple taps,
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
Is that all. Sounds like a piece of cake.
Regards.
Max. K 4 O DS.
- Original Message -
From: cdel...@juno.com
To: time-nuts@febo.com
Sent: Sunday, September 14, 2014 12:16 PM
Subject: [time-nuts] Hydrogen Maser KIT!
Well, I bet that got your attention!
My Hydrogen Maser kit
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
Bob,
On 09/15/2014 06:23 PM, Bob Stewart wrote:
My daughter and I were discussing what she does for a living with time and phase as a
geophysicist and relating that to what I'm trying to do with my GPSDOengine. I explained
that I was trying to keep the frequency accurate and stable, while
dave.martind...@gmail.com said:
Is there any reason (other than cost) not to both series-terminate the
source and parallel-terminate the sink?
With both series and parallel termination, the signal at the receiver is 1/2
the output level of the output driver. That doesn't work well if you
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.
I am sure you can make a case for some condition(s) where an unterminated
cable will still work. But it is not something we have
Hi Corby,
Looks like a nice challenge and lots of fun and learning.
A maser or two would not be bad for my lab :)
Those Sigma-Taus is known to be pressure sensitive. Might be something
to investigate.
Cheers,
Magnus
On 09/14/2014 07:16 PM, cdel...@juno.com wrote:
Well, I bet that got
Hi
These are saturated logic signals. When you terminate both source and load you
get an interesting issue with compatible logic levels.
For instance: 5V CMOS switches at roughly 2.5V. If you series terminate and
load terminate, your destination now sees a 0 to 2.5V signal. Either it’s
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
Thanks for the details.
This miniaturized device is nice.
There is no information regarding stability. Anything there ? What's the
technology inside ? crystal, TCXO ?
What is the approx price for a such device ?
The VCXO I was targetting is this one :
has anyone suggested a 50R in series with a capacitor as termination?
no DC currents
Best
Richard
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Hi Stephane,
our customer just needed +/-50KHz free-running over all conditions
including aging, so stability was not of major concern, and the unit easily
performs significantly better than that. We did make a VCO version for PLL
disciplining so you can lock it to a GPSDO or in a
Thanks for your feedback. This is indeed a bit expensive for that application.
The x5 multiplier is indeed just the harmonic 5 capture with the helical
filter. I'll let you know the outcome. This probably won't beat any expensive
ULN source but might be a good starting point for low cost. Worth
We've been on the new version of Mailman for a couple of weeks now. The
main reason for the update was to work around the DMARC adoption by
Yahoo, AOL, and other large ISPs that broke the mailing list model.
That seems to be working now. I'll spare the technical details (you can
read about it
I should drop an email rather than just lurking on this extremely
interesting list.
I'm in the process of building my first GPSDO, so I have lots to learn
and am enjoying the education. This list has been a real eye opener
for me.
I'm a licensed amateur radio operator looking to move up into
Jason, we just did one using the ublox at 1 KHz and I have some boards
extra so if you contact me off list I will gladly send you some data and
schematic .Can be modified for 10 KHz.
Bert Miami
In a message dated 9/15/2014 9:46:35 P.M. Eastern Daylight Time,
ja...@ball.net writes:
I
depend how do you terminate the, cable if the cable's impedance is Z,
use two terminating resistors each R =2Z, one is connected to thee
ground the other is connected to the supply voltage of the receiving
chip, that way although the cables input and output termination will
eat up half of the
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