Hey Denis,
thanks for putting this doc together - it's very interesting to me as a TDR
n00b to see a case study with images and calculations.
As for the correction, I take no credit, as several other people noticed
this before me, starting perhaps with Albert Otten, who quipped "Most
remarkable is the slow speed of light in vacuum in the USA ;-)".
Siggi
On Mon, Apr 29, 2019 at 9:20 PM Dennis Tillman W7PF <dennis@...>
wrote:
Hi Siggi,
YIKES! Thanks for catching my error. That was a very stupid typo I made. I
know the speed of light by heart.
I was getting tired when I was doing that part of the write-up and I
remember I was very annoyed at myself that I was having trouble
concentrating.
I revised my calculations. The new Velocity Factor is 0.678 which is much
more common. The diameter of the 012-0482-00 cable is 0.210 inches and it
is stiffer than other coax due to the double shield. Since RG223/U is
double shielded, has a diameter of 0.213inches, and has a Velocity Factor
of 0.67 this may be the coax that Tek used to make these cables. There is
still another thing that needs to be located to make a replacement cable -
locate a true 50ohm BNC connector. Most BNC connectors are not 50ohms. They
can, and do, vary between 50 to 54ohms to match to the different impedances
of supposedly 50ohm cable (which also can vary between 50 to 54ohms).
I just uploaded a revised copy of my evaluation with the corrected formula
and value and a few other changes to clarify my conclusions.
I deleted the previous document. The revised document is at
/g/TekScopes/files/Evaluation%20of%20the%20Tektronix%20012-0482-00%20cable%20for%20the%20SG503%20REVISED.pdf
The corrected document says REVISED right in the title and in the footnote
at the bottom.
Albert Otten's email seems right on cue. Let us know how your RG223 cable
works out.
Dennis Tillman W7PF
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of
Siggi
Sent: Monday, April 29, 2019 10:51 AM
To: [email protected]
Subject: Re: [TekScopes] My TDR Evaluation of the SG503 012-0482-00
Cable has been uploaded
On Mon, Apr 29, 2019 at 1:40 PM Dennis Tillman W7PF
<dennis@...>
wrote:
Hi Albert,
I think my derivation is valid and I know the VF can't be that high.
Did I leave something out in the way I calculated it?
You misstated the sped of light in vacuum, which is 299792458m/s per
Wikipedia, whereas your doc states "The speed of light in a vacuum is
224844343.5m/Sec = 0.2248m/nSec.", which is a 25% error :).
