Safely getting the electrical length of a connected antenna feedline
Chris, that makes sense. The low cost Chinese microscopes seem to have only one magnification, usually 20x, probably too much for circuit work. Also the stage is such that only a limited size board can be accommodated. The ideal would be a stereo head on a boom, with magnification adjustable from say 3x to 20x more or less. I don't know where to get such an animal at a decent price.
I would only use this occasionally so investing substantial money isn't in the cards. Perhaps someone has one to trade or to sell at a price I can justify.
Bob
On Thursday, August 11, 2016 8:37 PM, Chris Albertson <albertson.chris@gmail.com> wrote:
There is quite a lot to know about stereo microscopes
The first decision is if you want to buy a new Chinese microscope or a
much older used professional grade US made scope. The Chinese units
used to be total junk but not any more, or at least some of them are
good. But at the $50 price point I doubt you are into the better
Chinese brands. That said, inspecting electrical parts does not
require a state of the art microscope. It is an easy task But
can't say much more until you get to talking about exact make and
model.
On Thu, Aug 11, 2016 at 10:24 AM, Bob Albert via time-nuts
time-nuts@febo.com wrote:
What are the important parameters regarding purchase of a stereo microscope? I see some on ebay for around $50; are those good?
Bob
On Thursday, August 11, 2016 10:00 AM, Didier Juges shalimr9@gmail.com wrote:
I concur. I have been using ExpressPCB extensively over the last 2 years
with great satisfaction now that it is possible to get Gerber files from
them.
I typically use the mini board pro service (3 bare boards, 2 sided with
solder mask and silk screen) for prototypes and then buy the Gerbers to
have production quantities done overseas.
The boards are of high quality and the service is very fast at a very
reasonable price.
The only gotcha with regard to Gerber files is that you can only buy
Gerbers for boards that you have actually bought from them, so the process
is to buy the prototypes, then if you are happy with those, buy the Gerbers
for that design.
Didier KO4BB
On Tue, Aug 9, 2016 at 3:06 PM, Brooke Clarke brooke@pacific.net wrote:
Hi:
I've had good luck using any of the the ExpressPCB services that include
solder mask with surface mount parts where the pitch is 0.05" (half normal
DIP) and hand soldering (requires stereo microscope).
http://www.prc68.com/I/BTSG.shtml (battery top signal generator)
http://www.prc68.com/I/Images/ICS525v1o.jpg
http://www.prc68.com/I/SMT.shtml http://www.prc68.com/I/SMT.shtml
--
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
The lesser of evils is still evil.
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Redondo Beach, California
Good point! It is only an issue when you try to calibrate/correlate to the physical length.
Didier
On August 11, 2016 1:56:09 PM CDT, Bob Stewart bob@evoria.net wrote:
Why is velocity factor an issue? Aren't we only interested in the
electrical time from one end of the coax to the other?
Bob
-----------------------------------------------------------------
AE6RV.com
GFS GPSDO list:
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From: Didier Juges <shalimr9@gmail.com>
To: Bob Albert bob91343@yahoo.com; Discussion of precise time and
frequency measurement time-nuts@febo.com
Sent: Thursday, August 11, 2016 1:20 PM
Subject: Re: [time-nuts] Safely getting the electrical length of a
connected antenna feedline
I used the PPS from a Thunderbolt (fast rise lime, low rep frequency,
was handy) and a digital storage scope and a couple of resistors to
make a reflectometer based on this experiment:
www.ko4bb.com/getsimple/index.php?I'd=coax-cable-impedance-matching
You can very clearly see a 50 ohm/75 ohm mismatch.
The biggest variable will be the velocity factor.
Didier KO4BB
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Sent from my Moto-X wireless tracker while I do other things.
Thank you Tom and yes, the spell checker tends to be overbearing at times
Didier
On August 11, 2016 3:19:04 PM CDT, Tom Van Baak tvb@LeapSecond.com wrote:
FYI: In Didier's post below, the correct URL is:
http://www.ko4bb.com/getsimple/index.php?id=coax-cable-impedance-matching
I'm guessing a mobile spell checker changed his " id= " to " I'd= "
(even though it was part of a URL).
/tvb
----- Original Message -----
From: "Didier Juges" shalimr9@gmail.com
To: "Bob Albert" bob91343@yahoo.com; "Discussion of precise time and
frequency measurement" time-nuts@febo.com
Sent: Thursday, August 11, 2016 11:20 AM
Subject: Re: [time-nuts] Safely getting the electrical length of a
connectedantenna feedline
I used the PPS from a Thunderbolt (fast rise lime, low rep frequency,
was handy) and a digital storage scope and a couple of resistors to
make a reflectometer based on this experiment:
www.ko4bb.com/getsimple/index.php?I'd=coax-cable-impedance-matching
You can very clearly see a 50 ohm/75 ohm mismatch.
The biggest variable will be the velocity factor.
Didier KO4BB
On August 8, 2016 2:18:02 PM CDT, Bob Albert via time-nuts
time-nuts@febo.com wrote:
I host a group called something like HF Antennas. There I posted a
link to an article on how to measure coaxial cable. The easiest way is
with a spectrum analyzer and a tracking generator.
You connect the generator to the analyzer through a Tee that goes to
the unknown coax. You will see a group of peaks and nulls over the
spectrum. The spacing is a half wave of the cable. The match needs to
not be good to see the nulls best, and you will need to know the
propagation constant of the cable. Chances are, the match won't be
good over the entire range so you are okay with that. Propagation
constant of most coaxial cable runs around 66%.
You can also use a TDR setup but you'll have to make one, with a
pulser
and a 'scope. I downloaded a circuit for a pulser that uses one IC. I
have the parts but haven't built it yet, as I am stalled by the
problem
of connecting to a 14 pin SMD part. The IC uses one part as an
oscillator and the other 5 in parallel to drive 50 Ohms. Again, you
use a Tee and measure the time for a reflection, bearing in mind that
the trip is two ways over the same cable and the time shown will be
double the time for the calculation.
Bob
On Monday, August 8, 2016 12:00 PM, Bob Stewart bob@evoria.net
wrote:
Earlier this year, with some help, I pulled the dish off of an old
DishTV antenna on the roof and put a 5V bullet antenna on the mast. I
also pulled a new cable through by attaching it to the old one. The
problem is that I was not able to measure the new cable. So, the
question is, without going back on the roof in this heat, how can I
measure the electrical length of the line I pulled?
I was thinking of using my 8640B signal generator and sending some RF
back up the line to get a quarter wavelength at the null. But that
assumes a lot, including that the other end is open at 3MHz, or
whatever the frequency works out to be, as well as that the high
voltage on the antenna end won't be high enough to blow the LNA.
So, how much RF I can safely send up the line? I've got an 8558B
spectrum analyzer, but it's not on the bench, and it would be easier
to
use my scope, which sadly is a 70s vintage Tek 455. Do I put this all
together with a lead from the generator to a tee at the measuring
device and tune for a null? My experience at getting precise
measurements on anything longer than a few inches is effectively none,
but I'd guess that I want less than 0.5V at the LNA during this test.
Oh, and I do have an 8444A tracking generator that can output -10 dbm
as well as a 10 db attenuator within easy access. That could get a
quick spot on the null point.
Most importantly, of course is the question of whether this will even
work.
Bob -
AE6RV
AE6RV.com
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The way ExpressPCB works is that their free software produces boards in a proprietary format, and you have to pay to convert their design file to Gerber.
Your mileage may vary but I found the combination of design tools learning curve, board quality and quick service to be worthwhile to me.
I have tried Eagle twice and never could manage to build the models I needed. It may have been an issue of not finding the right tutorial but I have produced several ExpressPCB designs in less time than I have tried (unsuccessfully) to produce a single schematic in Eagle, let alone a PWB. Since it is a hobby that has become a business, time matters to me, design time and delivery.
At that point, the cost of the Gerber becomes somewhat irrelevant.
Note that you can make boards of any size in ExpressPCB.
I am not advocating it is the best solution for everyone, I personally would like to be proficient with Eagle, but Express PCB works for me.
Didier KO4BB
On August 11, 2016 10:45:45 PM CDT, Chris Albertson albertson.chris@gmail.com wrote:
This seems totally backwards. Typically a Gerber file is something
you make yourself on your computer then send it in for a prototype.
Seems odd to buy them.
I checked ExpressPCB prices and they are very high. I can get PCBs
made quickly in the US for $3 per square inch, shipping included with
$9 minimum order. And you don't buy the Gerbers.
I notice ExpressPCB offers free software. But it is totally
non-standard and you can't use it for anything other then for their
service. Most people needing free PCB software use Eagle, some use
Kicad or some others. But Eagle seems to be kind of a universal
standard.
On Thu, Aug 11, 2016 at 8:55 AM, Didier Juges shalimr9@gmail.com
wrote:
I concur. I have been using ExpressPCB extensively over the last 2
years
with great satisfaction now that it is possible to get Gerber files
from
them.
I typically use the mini board pro service (3 bare boards, 2 sided
with
solder mask and silk screen) for prototypes and then buy the Gerbers
--
Chris Albertson
Redondo Beach, California
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to
https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
--
Sent from my Moto-X wireless tracker while I do other things.
Because Velocity Factor determines the time it takes a EM wave to traverse the cable it ALSO shortens the wavelength by the same amount relative to free space this is why coaxial cables can be used as delay lines and why when cutting resonant sections of coaxial cable the Velocity Factor must be known
Content by Scott
Typos by Siri
On Aug 11, 2016, at 2:56 PM, Bob Stewart bob@evoria.net wrote:
Why is velocity factor an issue? Aren't we only interested in the electrical time from one end of the coax to the other?
Bob
AE6RV.com
GFS GPSDO list:
groups.yahoo.com/neo/groups/GFS-GPSDOs/info
From: Didier Juges <shalimr9@gmail.com>
To: Bob Albert bob91343@yahoo.com; Discussion of precise time and frequency measurement time-nuts@febo.com
Sent: Thursday, August 11, 2016 1:20 PM
Subject: Re: [time-nuts] Safely getting the electrical length of a connected antenna feedline
I used the PPS from a Thunderbolt (fast rise lime, low rep frequency, was handy) and a digital storage scope and a couple of resistors to make a reflectometer based on this experiment:
www.ko4bb.com/getsimple/index.php?I'd=coax-cable-impedance-matching
You can very clearly see a 50 ohm/75 ohm mismatch.
The biggest variable will be the velocity factor.
Didier KO4BB
time-nuts mailing list -- time-nuts@febo.com
To unsubscribe, go to https://www.febo.com/cgi-bin/mailman/listinfo/time-nuts
and follow the instructions there.
Hi
You can get a pretty good microscope new for about $1,000. Getting them used is a hit or
miss process. A lot of this stuff actually works very well when in good condition with all the
parts (The Mantis is one example). Without all the parts they don’t work or work poorly.
For most of what you do, there is no need for anything fancy. There is a Mantis in full working
condition at work. It never gets used. Magnifier lights get used a lot. Low magnification
microscopes with really good halogen / fiber optic ring lights seem to be the most
popular option.
Bob
On Aug 11, 2016, at 8:06 PM, Steve steve65@suddenlink.net wrote:
Can anyone compare the stereo microscope to a camera/monitor for use with SMT? I have a cheap stereo microscope that I would like to replace with either a much better stereo microscope or a camera/monitor. Is there a marked advantage(s) of one versus the other? I have no "floaters" to contend with.
Steve, K8JQ
On 8/11/2016 4:06 PM, Chuck Harris wrote:
Lots of good suggestions have already been made, but for
me, a boom style stereo microscope, with a distance between
the objective, and the focal point of at least 3 inches works
fairly well...
One other thing that may force your decision, if you are
older, your eyes will likely have lots of "floaters", which
are debris that floats around in your eyeballs. This debris
floats in and out of the center of your field of view, and
looks like a bunch of translucent worms, or shadows.
Your brain, the magnificent organ that it is, tries to compensate
for your eye's degradation, and as long as your eyes can move
about in your field of view, it effectively removes the floaters
from the scenes you are viewing.
However, if you use a stereo microscope, your eye position
is fixed by the very limited amounts of off axis motion
that will allow a through optical channel. This lack of off
axis motion will emphasize your floaters in a great way, and you
will see every single one, clearly, as if it were something
you really wanted to view. Some times, the floaters will cover
the exact thing you need to see clearly, and you will have to
move it off axis by moving it on the microscope stage.
The only answer to this problem, is to either have perfect eyes,
or to use a microscope where you are looking at a screen, rather
than through a pair of oculars. This way, your eyes can dart
around, and inspect what they need to see clearly, and the
floaters will be ignored by your brain.
As far as I know, there is only one optical microscope built this
way, and it is the very expensive Mantis.
Because of the great expense of flat screen optical microscopes,
most modern SMD viewing equipment is going to the trivially cheap
method of using a CCD/CMOS color video camera and an LCD screen.
You can do a lot with a cheap USB camera mounted to a boom, a fiber
optic light source, or a ring light, and a laptop computer to
display the image.
-Chuck Harris
Bob Albert via time-nuts wrote:
What are the important parameters regarding purchase of a stereo microscope? I
see some on ebay for around $50; are those good? Bob
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Yes however since you are simply submitting the circuit design it makes sense that they would hold the Gerber until you bought prototypes as unless you have software to create the Gerber it has value as once you have the Gerber you can have the boards built anywhere. They need to make a profit to stay in business after all
Content by Scott
Typos by Siri
On Aug 11, 2016, at 11:45 PM, Chris Albertson albertson.chris@gmail.com wrote:
This seems totally backwards. Typically a Gerber file is something
you make yourself on your computer then send it in for a prototype.
Seems odd to buy them.
I checked ExpressPCB prices and they are very high. I can get PCBs
made quickly in the US for $3 per square inch, shipping included with
$9 minimum order. And you don't buy the Gerbers.
I notice ExpressPCB offers free software. But it is totally
non-standard and you can't use it for anything other then for their
service. Most people needing free PCB software use Eagle, some use
Kicad or some others. But Eagle seems to be kind of a universal
standard.
On Thu, Aug 11, 2016 at 8:55 AM, Didier Juges shalimr9@gmail.com wrote:
I concur. I have been using ExpressPCB extensively over the last 2 years
with great satisfaction now that it is possible to get Gerber files from
them.
I typically use the mini board pro service (3 bare boards, 2 sided with
solder mask and silk screen) for prototypes and then buy the Gerbers
--
Chris Albertson
Redondo Beach, California
time-nuts mailing list -- time-nuts@febo.com
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and follow the instructions there.
I have never used the Mantis, though I considered one when
my eyes started to degrade.
My big problem with the mantis is all of the light that is
projected on the viewing screen has to be reflected from the
device being viewed. That means you are throwing a lot of
heat and lumens at the device, and even with that you cannot
work in a brightly lit room.... the projected screen will be
too dim.
Just about any CCD/CMOS camera meant for use as a CATV camera,
when equipped with a good quality macro zoom lens, would work
nicely for SMT work. A long working distance, is essential,
which means good lenses. I think it would take very little
expense and effort to greatly exceed the abilities of the
Mantis.
I, on the other hand, continue to use an Olympus Stereo Zoom
microscope (model SZH), and a not so cheap Russian copy of
another Olympus Stereo Zoom scope. And live with a tableau
of translucent worms that cover everything I view.
You get used to it...
-Chuck Harris
Brooke Clarke wrote:
Hi Chuck:
The Mantis is very expensive and the arm in the EEVblog review is not as stable as my
arm.
https://www.youtube.com/watch?v=a3o0EWHEH08
about US$ 3300 retail, maybe $2000 eBay.
In the review he is confused about 3D vs. perspective.
The working distance does not look as long as the B&L.
http://www.prc68.com/I/SMT.shtml#Mag
In the past when I had access to magnifying lamps and stereo
microscopes suitable for printed circuit board work, I preferred the
former. The extra magnification of the stereo microscopes was not
needed and the large magnifying lamp was easier on the eyes although
admittedly I wore glasses even then.
On Fri, 12 Aug 2016 09:14:26 -0400, you wrote:
Hi
You can get a pretty good microscope new for about $1,000. Getting them used is a hit or
miss process. A lot of this stuff actually works very well when in good condition with all the
parts (The Mantis is one example). Without all the parts they dont work or work poorly.
For most of what you do, there is no need for anything fancy. There is a Mantis in full working
condition at work. It never gets used. Magnifier lights get used a lot. Low magnification
microscopes with really good halogen / fiber optic ring lights seem to be the most
popular option.
Bob
Hi Chris:
ExpressPCB has very easy to use free software for schematic capture (later used to check the board wiring) and software
for board layout including making custom components if their library of stock components does not have what you need.
The output file format is proprietary, which makes it interesting that Far Circuits can read it.
I just have not wanted to go through learning curve for Gerber files and all the associated stuff (maybe drilling, silk
screen, solder mask) which is very easy to do with ExpressPCB.
When you start buying many circuits per board and a number of boards from the the price gets a lot lower. When I try
Far Circuits I expect it to drop by a small integer (1/2, 1/3 . . 1/4?)..\
--
Have Fun,
Brooke Clarke
http://www.PRC68.com
http://www.end2partygovernment.com/2012Issues.html
The lesser of evils is still evil.
-------- Original Message --------
This seems totally backwards. Typically a Gerber file is something
you make yourself on your computer then send it in for a prototype.
Seems odd to buy them.
I checked ExpressPCB prices and they are very high. I can get PCBs
made quickly in the US for $3 per square inch, shipping included with
$9 minimum order. And you don't buy the Gerbers.
I notice ExpressPCB offers free software. But it is totally
non-standard and you can't use it for anything other then for their
service. Most people needing free PCB software use Eagle, some use
Kicad or some others. But Eagle seems to be kind of a universal
standard.
On Thu, Aug 11, 2016 at 8:55 AM, Didier Juges shalimr9@gmail.com wrote:
I concur. I have been using ExpressPCB extensively over the last 2 years
with great satisfaction now that it is possible to get Gerber files from
them.
I typically use the mini board pro service (3 bare boards, 2 sided with
solder mask and silk screen) for prototypes and then buy the Gerbers