Bruce,
I finally found the time to google for avalanche pulse generator and
found an App note from Zetex on the subject.
I was not familiar with this technology, but it seems interesting.
Amazing that you can get 50A pulses with sub-ns rise time out of a
device in an SOT-23 (or TO-92) package!
Didier
Analog sampling scopes used avalanche transistors to drive the snap off
diode shorted delay line pulse generator which in turn drove the diode
sampling gate with picosecond risetime complementary pulses.
Bruce
Didier Juges wrote:
Bruce,
I finally found the time to google for
Hi Didiere:
There's also an app note at Linear Technology for making pulses so fast
they are used to calibrate sampling scopes.
Some years ago I made a very simple circuit that pulses a LED with many
amps (very short time) based on a transistor going into avalanche.
Have Fun,
Brooke Clarke
Hi Brooke,
I am familiar with the Jim Williams app note, but I felt the pulse shape
was somewhat lousy (based on the pictures that came with the article)
due to the very small cap on the collector, OK to calibrate or evaluate
a fast scope, I guess, but too far from a square wave to be able to
Hi Brooke,
acc. my understanding, the characteristic impedance of a transmission
line (ideally losseless) is constant and waveform independant, as
given by the relation of inductive and capacitive values (muh and epsilon)
equally distributed over the line.
As long as the physical parameters
- Original Message -
From: Arnold Tibus [EMAIL PROTECTED]
To: Discussion of precise time and frequency measurement
time-nuts@febo.com
Sent: Tuesday, January 30, 2007 4:09 AM
Subject: Re: [time-nuts] 75Z vs 50Z for GPS receivers
Hi Brooke,
acc. my understanding, the characteristic
Subject: Re: [time-nuts] 75Z vs 50Z for GPS receivers
Hi Brooke,
acc. my understanding, the characteristic impedance of a
transmission
line (ideally losseless) is constant and waveform independant, as
given by the relation of inductive and capacitive values (muh and
epsilon)
equally distributed
Dave Brown said, in part,
The characteristic impedance of a transmission
line, in purely general terms, is given by the square root of R plus
jw L divided by G plus jw C, with the usual meaning for symbols used.
Well, I know most of those symbols, but what's gravity (G) doing in
that equation?
Hi Bill:
The series elements are resistance and inductance.
The shunt elements are conductance G (leakage resistance expressed in
Mho or Siemens) and capactance
For long lines the resistance of the wires is very important and for low
frequencies the capactance is the dominant reactance.
see the
acc. my understanding, the characteristic impedance of a transmission
line (ideally losseless) is constant and waveform independant,
The catch is we are discussing the non-lossless case.
The corner frequency is where the losses become significant.
I think there is another corner where the
Hi Hal:
The corner frequency is mainly becuase of the capactance at low
frequencies. A transmission line at audio frequency looks like a shunt
capacitor and the inductance no longer is working aginst it, so you
don't get a real Zo but instaed capactance. Loss really does not come
into it.
Most (except for Trimble,..) GPS receivers and antennas
are designed to use 50 ohm cable.
Trimble Bullet GPS antennas have a 50 ohm output impedance.
Trimble literature however is ambiguous in that in the
Resolution T receiver datasheets talk about using RG59
to connect to the antenna.
Christopher Hoover wrote:
Most (except for Trimble,..) GPS receivers and antennas
are designed to use 50 ohm cable.
Trimble Bullet GPS antennas have a 50 ohm output impedance.
Trimble literature however is ambiguous in that in the
Resolution T receiver datasheets talk about using RG59
to
In message [EMAIL PROTECTED], Dr Bruce Griffiths writes:
93 ohm RG62 cables with BNC connectors are not unknown, they were used
in some nuclear instrumentation.
I have a few of these lying around.
Other uses:
93 Ohm: IBM 3270 terminal cabling
75 Ohm: Practically all telecoms
Christopher Hoover said the following on 01/28/2007 04:48 AM:
I would also add that BNC and N connectors come in both 50Z and 75Z flavors.
In fact 75Z BNC connectors are pretty common, being used in professional
video applications. (Check surplus BNC patch cords carefully.) On the
other
] [mailto:[EMAIL PROTECTED] On
Behalf Of Poul-Henning Kamp
Sent: Sunday, January 28, 2007 6:20 AM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] 75Z vs 50Z for GPS receivers (was Re: ACE-III
GPSreceivers (Dr Bruce Griffiths))
In message [EMAIL PROTECTED], Dr Bruce
Dr Bruce Griffiths wrote:
Christopher Hoover wrote:
Most (except for Trimble,..) GPS receivers and antennas
are designed to use 50 ohm cable.
Trimble Bullet GPS antennas have a 50 ohm output impedance.
Trimble literature however is ambiguous in that in the
Resolution T receiver
Didier Juges wrote:
Dr Bruce Griffiths wrote:
Christopher Hoover wrote:
Most (except for Trimble,..) GPS receivers and antennas
are designed to use 50 ohm cable.
Trimble Bullet GPS antennas have a 50 ohm output impedance.
Trimble literature however is ambiguous in that in the
Chris
Christopher Hoover wrote:
Most (except for Trimble,..) GPS receivers and antennas
are designed to use 50 ohm cable.
Trimble Bullet GPS antennas have a 50 ohm output impedance.
Trimble literature however is ambiguous in that in the
Resolution T receiver datasheets talk
Dr Bruce Griffiths wrote:
Didier Juges wrote:
Dr Bruce Griffiths wrote:
Christopher Hoover wrote:
Most (except for Trimble,..) GPS receivers and antennas
are designed to use 50 ohm cable.
Trimble Bullet GPS antennas have a 50 ohm output impedance.
Trimble
Dr Bruce Griffiths wrote:
Chris
Christopher Hoover wrote:
Most (except for Trimble,..) GPS receivers and antennas
are designed to use 50 ohm cable.
Trimble Bullet GPS antennas have a 50 ohm output impedance.
Trimble literature however is ambiguous in that in
HI Didier:
It's my understanding that the term impedance can only be applied when
sine wave signals are being used. So for pulse work you might look at
the harmonic content and try to match all those frequencies.
Long ago Bob Grove promoted the idea of using 75 Ohm TV coax for ham
antennas
On Sun, 28 Jan 2007 13:02:39 -0800, Brooke Clarke [EMAIL PROTECTED]
wrote:
Long ago Bob Grove promoted the idea of using 75 Ohm TV coax for ham
antennas at 2 meters and higher frequencies because it had lower loss
than 50 Ohm coax and was much lower in cost. For ham applications the
VSWR due
Didier Juges wrote:
Dr Bruce Griffiths wrote:
Didier Juges wrote:
Dr Bruce Griffiths wrote:
Christopher Hoover wrote:
Most (except for Trimble,..) GPS receivers and antennas
are designed to use 50 ohm cable.
Trimble Bullet GPS
Didier Juges wrote:
Dr Bruce Griffiths wrote:
Chris
Christopher Hoover wrote:
Most (except for Trimble,..) GPS receivers and antennas
are designed to use 50 ohm cable.
Trimble Bullet GPS antennas have a 50 ohm output impedance.
In message [EMAIL PROTECTED], Dr Bruce Griffiths writes:
I can see the difference between the short 50 ohm cable terminated in 50
ohms and the short 50 ohm cable terminated in 75 ohms.
It would be instructive to repeat this with a short length of 75 ohm
cable terminated in50 and 75 ohms.
The
Poul-Henning Kamp wrote:
In message [EMAIL PROTECTED], Dr Bruce Griffiths writes:
I can see the difference between the short 50 ohm cable terminated in 50
ohms and the short 50 ohm cable terminated in 75 ohms.
It would be instructive to repeat this with a short length of 75 ohm
cable
It is true is that the impedance of a transmission line is not constant
with frequency, particularly at the low end (audio).
At the higher end, a lot of things happen, such as impedance,
attenuation and velocity factor all change (a little) with frequency.
Also, at the higher end, leakage
Dr Bruce Griffiths wrote:
Didier Juges wrote:
Dr Bruce Griffiths wrote:
Chris
Christopher Hoover wrote:
Most (except for Trimble,..) GPS receivers and antennas
are designed to use 50 ohm
Didier Juges wrote:
It is true is that the impedance of a transmission line is not constant
with frequency, particularly at the low end (audio).
At the higher end, a lot of things happen, such as impedance,
attenuation and velocity factor all change (a little) with frequency.
Also, at the
Didier Juges wrote:
Dr Bruce Griffiths wrote:
Didier Juges wrote:
Dr Bruce Griffiths wrote:
Chris
Christopher Hoover wrote:
Most (except
Didier Juges wrote:
Bruce,
You have done it again. Now, I have more ideas for interesting
experimentation and still not more time :-)
I have 3 coax runs going from my ham shack to the top of my tower to
feed the HF (14 to 30 MHz) and two VHF antennas (6m and 2m, or 50 MHz
and 144 MHz).
Hi Didier:
The Tek 1502 is great for doing this, especially if you have the
optional strip chart recorder. It's what it was made to do.
http://www.pacificsites.com/~brooke/Tek1502.shtml
Have Fun,
Brooke Clarke
w/Java http://www.PRC68.com
w/o Java
I think that the simplest explanation for the BIPM's recommendation that
the antenna cables be matched to the antenna output impedance and the
GPS receivers input impedance is as follows:
If one has gone to the trouble and expense of installing an antenna that
is relatively insensitive to
Hi Didier:
Yes they are on eBay. The tunnel diode models have a narrower pulse
than the later models that use something more rugged. Probably for all
practical purposes one of the newer ones would work well and last
better. I think the military bought boat loads of these and I've heard
a
narrowband receiver.
Daun
-Original Message-
From: [EMAIL PROTECTED] [mailto:[EMAIL PROTECTED] On Behalf
Of Brooke Clarke
Sent: Sunday, January 28, 2007 10:35 PM
To: Discussion of precise time and frequency measurement
Subject: Re: [time-nuts] 75Z vs 50Z for GPS receivers
Hi Didier
Certainly a vector network analyzer is the next piece of test equipment
I need to get. We have several HP 8720 and 8722 where I work, and it's
easy to be spoiled...
Unfortunately, that's another quantum leap in cost from the spectrum
analyzers and synthesizers I have, at least for those that
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