Re: My TDR Evaluation of the SG503 012-0482-00 Cable has been REVISED
All, I have been following this thread with interest; thanks to Dennis for his investigation and sharing. If anyone needs a refresher on the basics of TDR, TEK has a relevant Application Note here: Shaun M Get Outlook for iOS<> ________________________________ From: [email protected] on behalf of Albert Otten <aodiversen@...> Sent: Tuesday, April 30, 2019 03:05 To: [email protected]Subject: Re: [TekScopes] My TDR Evaluation of the SG503 012-0482-00 Cable has been REVISED Hi Dennis, Please read my following comment also with a smiley. "That was a very stupid typo I made." The speed of light you used previously was exactly 75% of the correct value. A remarkable typo ;-) I think you had a VF 75% in mind for some reason. Albert
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Re: OT: historical interest-- automobile radio coax
It is RG-62, 93 Ohm coax. The connector was designed by Galvin Manufacturing which changed their corporate name to Motorola to better identify their newly developed car radios.
IBM also used RG-62 for some of their dumb terminals for the 360 and later series.
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Re: My TDR Evaluation of the SG503 012-0482-00 Cable has been REVISED
Hi Dennis,
Please read my following comment also with a smiley.
"That was a very stupid typo I made."
The speed of light you used previously was exactly 75% of the correct value. A remarkable typo ;-)
I think you had a VF 75% in mind for some reason.
Albert
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Some 15 years ago I bought this scope from usa intending to recap it .
10 years ago I bought all the parts according to an on line spreadsheet. and thats as far as it got. because father time was working away I now don't feel competent to do the job, and probably never was ( not a tech but a ham)
Is there anyone in OZ preferable melbourne that could undertake such work. The scope was working when I fired it up last shortly after purchase but did have a slightly unstable display. I have not fired it up since as I thought it unwise to do so.
I see parts are available from israel for this as you will be aware If I need to repurchase the parts.
It used to be that eBay used to advertise an overhaul service but that seems to have long gone.
Any help would be appreciated.
73
George VK3QP
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Looking for fan impeller fastener for 2465
Does anyone have or sale or a source for the impeller fastener, Tek P/N: 343-104-001?
Thanks in advance.
Jon
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Re: OT: historical interest-- automobile radio coax
I do not have a specification, but a story.
A year ago I got around to investigating why the front fender mounted antenna on my 1966 Corvair was not working, infinite resistance from Motorola plug to the antenna shaft.
I suspected a bad ground from base to fender (did not explain infinite resistance, but common problem) or bad connection at the bottom of the antenna. GM antennas of this era usually have a screw on plug connection at the base of the antenna.
I unscrewed the coax from the antenna, and removed it from the car. Investigation revealed the center conductor, a small 30 or so awg copper wire had corroded and disappeared in places! So I ran a new piece of 30 awg wire through the (compared to the inner 30 awg conductor) large plastic tube that holds the center conductor inside the outer braid and soldered it to the Motorola plug and the GM connector.
Works GREAT!
Somewhere here I have several lengths of original Wards Antenna coax I picked up almost 50 years ago from Avec Electronics in Richmond, VA...... That's when I first noticed the tiny center conductor inside a large cavern of plastic tube inside the outer braid.
Not sure this is limited to early auto radio, as I cut into an antenna coax on a mid 80s Nissan truck, and it was the same small conductor in large tube construction. But, maybe 80s is early, now!
Frank DuVal
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On 4/29/2019 3:26 PM, Brad Thompson wrote: Hello--
This is off-topic and only of historical interest, but does anyone have a spec for
the coaxial cable used in early automobile-radio installations?
(For newcomers, automobile radios received only AM broadcasts until the first
AM/FM radios were introduced in the mid-1950s.) The AM installation used a short
telescoping whip antenna that "looked" capacitive to the radio's input.
To minimize shunt capacitance, the coax that connected antenna to radio
comprised a thin center conductor located inside a plastic tube covered with
a loosely-braided shield and an outer jacket of black plastic. The cable
terminated in a "Motorola connector" that was coaxial but likely
not otherwise spec'ed for impedance. The radio typically included a trimmer
capacitor which would allow boosting reception at either end of the AM band.
73--
Brad? AA1IP
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My TDR Evaluation of the SG503 012-0482-00 Cable has been REVISED
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 :).
-=-=-=-=-=-=-=-=-=-=-=- -----Original Message----- From: Albert Otten Sent: Sunday, April 28, 2019 11:39 PM Subject: Re: [TekScopes] My TDR Evaluation of the SG503 012-0482-00 Cable has been uploaded I?m going to solder a 1m RG223 cable for my SG503 so this is interesting stuff for me. Nice detailed piece of work Dennis, thanx!! -- Dennis Tillman W7PF TekScopes Moderator
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Re: 475A with High +110 rail
Tom,
I found all the advice helpful. Any comments and advice is greatly appreciated! Your confirmation of Dave's diagnosis is a great help, going back through his comments as well. I am reading the Power Supply circuit description in the manual right now. Unfortunately, I am not that experienced with this stuff, which does complicate things somewhat. However, i am not afraid to learn and fix things. Working through the components list right now. I do appreciate your followup and your kind advice. I will post more measurements and findings as I am able to get them from the scope.
Sincerely,
--
Michael Lynch
Dardanelle, AR
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Re: 475A with High +110 rail
This morning you got a nice reply from Dave Hills that talked about the parts of the circuit in question that limit and control the over voltage of the +110 circuit.
This led me to? search the 475A service manual and read everything it had to say about the low voltage regulator circuits.
There is a nice summary of how the +110 control low voltage circuit handles the over current and over voltage shutdowns.
After reading this, Dave Hills comments are probably right on the likely problem components. Your +110 regulator should probably shutdown with the over voltage you are seeing on the +110 test point, but it isn't!
Think about studying that +110 section on page 3-24 of my first edition August 1976 manual, it's all quite simple when you read it.
tom jobe...
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On 4/29/2019 3:23 PM, Mlynch001 wrote: I forgot to say Thanks to All for such complete answers. I appreciate your patience with a very inexperienced individual.
I will post results.
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Re: 2465B Parametric Freq Measurement Error
Thanks Chuck,
Don't worry, you never saw this machine - it's sort of my beater.
best,
john
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On 4/29/19 9:45 AM, Chuck Harris wrote: Hi John,
Best would be to swap the trigger hybrid from one of your
2465 family scopes that does work into the one that doesn't
work, as a test. (as long as you restore the original to the
calibrated scope, there will be no affect on calibration.)
The trigger hybrid is crucial to everything in the parametric
functions.
An additional place to look would be to follow the signal from the
DAC to the trigger hybrid threshold inputs (TLA, TLB). The 4051's
and the TL072's and their associated sample and hold gate parts go
bad sometimes (U2521, U2520, U2420, C2421, C2621).
One repair/calibration blurs into the next. If you think I didn't
repair something correctly, send it back, and I will fix it gratis.
I know I tested the parametric functions on the unit I calibrated.
It is a standard part of the tektronix calibration routines.
-Chuck Harris
John Ferguson via Groups.Io wrote:
Hi Chuck,
The parametric functions do not work on one of my 2445Bs, the one you didn't
calibrate.? It also doesn't sync on signal on start-up but does work well manually.?
I chased this around? on EVblog a few years back, but never arrived at what to look at.
Is it possible that cleaning up the contacts and gently re-seating a hybrid could
resolve this? Would it make sense to buy a replacement hybrid just in case the
clean-up doesn't produce the desired result?
best regards
john
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Re: My TDR Evaluation of the SG503 012-0482-00 Cable has been uploaded
I know the length, and from that can calculate the velocity factor. Or rather, let the 1502b calculate the factor for me. On 29/04/2019, Merchison Burke via Groups.Io <merchison@...> wrote: You need to get the specifications (using the part number on the cable)
which you are going to use (or test) and plug-in the Velocity factor
into the 1502 for the distance reading to be correct.
On 2019-Apr-29 4:03 AM, Tom Gardner wrote:
Very timely: this weekend I picked up a Tek 1502B, and it came with a
012-0482-00 cable and a 011-0123-00 BNC 50ohm terminator. Apart from
that I only have "generic" connectors and terminators, of variable
quality.
Caveat: I don't understand the expected performance of the 1502B, and
haven't calibrated it at all.
Having said that, the only significant difference from your report is
the velocity factor. In order for the 1502B to show the cable's length
as 3ft, I have to set the velocity factor to 0.67.
On 29/04/19 01:19, Dennis Tillman W7PF wrote:
I uploaded the results of my testing the SG503 012-0482-00 cable. In
addition I compared it to two other similar cables: a Tektronix
012-0057-00
50? cable, and a Pomona Electronics 50? cable.
It is located at:
/g/TekScopes/files/Evaluation%20of%20the%20Tektronix%20012-
0482-00%20cable%20for%20the%20SG503.pdf
Dennis Tillman W7PF
---
This email has been checked for viruses by AVG.
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Re: 475A with High +110 rail
I forgot to say Thanks to All for such complete answers. I appreciate your patience with a very inexperienced individual.
I will post results.
--
Michael Lynch
Dardanelle, AR
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Re: 475A with High +110 rail
Dave,
No worries on the caps! I understood why you were using them, I sometimes do the same thing and hope that people figure out my meaning. Renee, Tom and Dave, I will do some more probing and post the results. I am tempted to lift one end of CR1489 and test it, out of circuit. BTW, it appears to be mounted correctly. I think I might have found a good Q1496 and I will try that as well, once I verify CR1489. I do have a service manual for the scope, so that makes repairs much more doable for me, since I am not an EE or trained in any way. Just a self taught enthusiast. I just love these old TEKTRONIX scopes.
--
Michael Lynch
Dardanelle, AR
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Re: OT: historical interest-- automobile radio coax
Dennis Tillman W7PF wrote on 4/29/2019 2:33 PM: A follow up bit of information which may matter with the SG503 cable:
Within Tek it came as a surprise to at least one very senior engineer I know
when he discovered that BNC connectors were NOT 50ohms. For an interesting
explanation on how we arrive at 50 and 75 ohms for common cables read the
paragraph titles "Choice of Impedance". <snip> Hello-- This is off-topic and only of historical interest, but does anyone have a spec for the coaxial cable used in early automobile-radio installations? (For newcomers, automobile radios received only AM broadcasts until the first AM/FM radios were introduced in the mid-1950s.) The AM installation used a short telescoping whip antenna that "looked" capacitive to the radio's input. To minimize shunt capacitance, the coax that connected antenna to radio comprised a thin center conductor located inside a plastic tube covered with a loosely-braided shield and an outer jacket of black plastic. The cable terminated in a "Motorola connector" that was coaxial but likely not otherwise spec'ed for impedance. The radio typically included a trimmer capacitor which would allow boosting reception at either end of the AM band. 73-- Brad? AA1IP
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Re: My TDR Evaluation of the SG503 012-0482-00 Cable has been uploaded
Dennis,
You have an error in the free space velocity which Albert mentioned indirectly.
Multiple reflection in the cable produces one or more poles in the transfer function. The SG503 may compensate for reflections from the ends of a 3 ft cable. However, something as basic as physical robustness of the cable may be the primary factor. Just making wild guesses.
I'm not at all familiar with the SG503, but I have been doing a lot of TDR of cables and connectors with my 11801. I see a lot of not quite 50 ohm cables from reputable vendors. It's a bit disappointing. It also leaves the question of how close are the connectors to 50 ohms and over what BW.
I suspect that the cable with the reflection in the middle was partially crushed or kinked at some point.
I'd really like to see the no cable case at a faster sweep rate, say no more than 100 ps/div.
You can see some of what I've been doing here:
170 in particular shows the reflection from a BNC-F to BNC-M connection between two cables which otherwise match. I'm fairly certain they came from the same spool of cable. The two cables are BNC to SMA jumpers a friend made up for me when I was singing the "Chinese Connector Blues".
Have Fun!
Reg
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Re: My TDR Evaluation of the SG503 012-0482-00 Cable has been uploaded
A follow up bit of information which may matter with the SG503 cable:
Within Tek it came as a surprise to at least one very senior engineer I know
when he discovered that BNC connectors were NOT 50ohms. For an interesting
explanation on how we arrive at 50 and 75 ohms for common cables read the
paragraph titles "Choice of Impedance".
In a few special cases where the need for exactly 50ohms was necessary Tek
had their own connectors made. The difference is so slight in mechanical
dimensions that you would never notice it, but Tek was a stickler for
details, and this detail mattered when you are designing high performance
equipment to laboratory standards.
I was not surprised when the Pomona cable I tested showed up on the TDR as
having an impedance of 50.6ohms. I expected it to measure 51 ohms before I
tested it. I check every cable I get at hamfests or swap meets when I bring
them home on a TDR before I will add them to my pile of coax cables. At
first I was always puzzled by the random variation in impedance on coax I
saw on the TDR within the same type of common cable designators. There are
several variations of RG-58 for example: Belden makes RG58 in 50 52, and
53.5 ohm versions. The make RG58A/U in 54 and 50 ohm versions. RG58,
RG58A/U, RG58C/U are common but other RG58 versions also exist.
With this much variation in cable impedance it is to be expected that the
connector manufacturers will come up with versions of their BNC to match
almost any impedance close to 50ohms. That is the problem Tek had that
forced them to do their own BNCs for special situations.
The hardest part of doing this evaluation was getting to the absolute
minimum Rho with the adapters and terminators I had to use. Almost all the
measurements were within 5mRho -10mRho. That is approaching the "noise
level" for the 7S12 which is just under 1mRho.
Another thing to watch out for are the transitions in the connector. The
last photo shows what happens to the signal when it traverses a poor quality
adapter. The resulting swing indicated a very large shunt capacitance facing
the signal before it reaches the end of its journey. Moral of this part of
my results: Don't rely on unknown quality adapters. Also, buy terminators
from reputable companies you trust, and if you have a TDR use it to check
the parts you buy.
Dennis Tillman W7PF
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-----Original Message-----
From: me
Sent: Sunday, April 28, 2019 5:19 PM
Subject: [TekScopes] My TDR Evaluation of the SG503 012-0482-00 Cable
has been uploaded
I uploaded the results of my testing the SG503 012-0482-00 cable. In
addition I compared it to two other similar cables: a Tektronix 012-
0057-00 50¦¸ cable, and a Pomona Electronics 50¦¸ cable.
It is located at:
/g/TekScopes/files/Evaluation%20of%20the%20Tektronix%20
012-
0482-00%20cable%20for%20the%20SG503.pdf
Dennis Tillman W7PF -- Dennis Tillman W7PF TekScopes Moderator
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Re: 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 :).
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Re: My TDR Evaluation of the SG503 012-0482-00 Cable has been uploaded
Hi Merchison,
I don't know about the 1502, but the 7D12 which I used has the ability to
preset any velocity factor on the POLY scale between 0.67 and Air (which is
one of the other distance scales). VF for air is around 0.99.
Dennis Tillman W7PF
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-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of
Merchison Burke via Groups.Io
Sent: Monday, April 29, 2019 10:25 AM
Subject: Re: [TekScopes] My TDR Evaluation of the SG503 012-0482-00
Cable has been uploaded
You need to get the specifications (using the part number on the cable)
which you are going to use (or test) and plug-in the Velocity factor
into the 1502 for the distance reading to be correct.
On 2019-Apr-29 4:03 AM, Tom Gardner wrote:
Very timely: this weekend I picked up a Tek 1502B, and it came with a
012-0482-00 cable and a 011-0123-00 BNC 50ohm terminator. Apart from
that I only have "generic" connectors and terminators, of variable
quality.
Caveat: I don't understand the expected performance of the 1502B, and
haven't calibrated it at all.
Having said that, the only significant difference from your report is
the velocity factor. In order for the 1502B to show the cable's length
as 3ft, I have to set the velocity factor to 0.67.
On 29/04/19 01:19, Dennis Tillman W7PF wrote:
I uploaded the results of my testing the SG503 012-0482-00 cable. In
addition I compared it to two other similar cables: a Tektronix
012-0057-00
50? cable, and a Pomona Electronics 50? cable.
It is located at:
/g/TekScopes/files/Evaluation%20of%20the%20Tektronix
%20012-
0482-00%20cable%20for%20the%20SG503.pdf
Dennis Tillman W7PF -- Dennis Tillman W7PF TekScopes Moderator
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Re: My TDR Evaluation of the SG503 012-0482-00 Cable has been uploaded
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?
My purpose in calculating it (regardless of whether I got a perfect answer) was to show how to do it so everyone else with a TDR could do it. I wanted to illustrate how Velocity Factor was calculated from a TDR display. Instead of looking up a standard Velocity Factor, I was attempting to determine the velocity factor of the Tek cable based on its physical length and the TDR's "time distance" electrical length I measured on the screen. So I measured the time between the discontinuity at the start and at the end of the trace on the screen. Take a look at Figure 2. I marked off the starting point at "A" and the ending point of the cable at "B" and measured 9.0nSec between points A and B on the screen. Then I calculated the velocity factor based on that measurement of the transit time of the pulse through a 36.0" cable.
The result I got, VF = 0.9 was very high and I commented on that in my results. The only cables that have such a high velocity factor are very expensive and usually very fat (large diameter). I know the velocity factor can't be 0.9 and that figure is only a guess because my TDR has not been calibrated in over 20 years. The VF is probably more likely around 0.8 which is still a general indication of a high quality cable.
I also converted the mRho measurements to VSWR figures in a few places because that is also a consideration for some applications. For instance, the VSWR is listed in the specs for the 7A29 plugin as 1.4:1 at 10mV/Div or 1.2:1 on all other settings. The VSWR of the 012-0482-00 cable may have been a consideration of the engineering staff that determined what properties it had to have for the SG503.
This raises another question which none of us may ever have the answer to: What are the unique qualities the Tek SG503 designer wanted this cable to have to be the ideal match to the SG503. It may be something as silly, in retrospect, as the stiffness of the cable. Maybe he/she like stiff cables. Why is it exactly 36in? Maybe he/she had a scrap piece of stiff coax exactly that length in his drawer and he/she said "Use this" to the production people when they asked what kind of cable should ship with the SG503. Meanwhile we are all guessing at whether using this cable with an SG503 is really important.
Dennis Tillman W7PF
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-----Original Message-----
From: Albert Otten
Sent: Monday, April 29, 2019 4:54 AM
Subject: Re: [TekScopes] My TDR Evaluation of the SG503 012-0482-00
Cable has been uploaded
On Mon, Apr 29, 2019 at 10:50 AM, Richard Knoppow wrote:
Where does it show the speed of light in a vacuum? The TDR should
be calibrated to the speed of light (electricity) in the cable. For 50
Ohm cable its about 66% of c. Varies with the impedance of the cable.
If you know the physical length of the cable you can determine both
its impedance and the velocity from it.
On 4/29/2019 1:26 AM, Albert Otten wrote:
Interesting stuff Dennis! I have to look at it in more detail. I
consider repeating these tests since I have both Tek cables, though
I don't have quality SMA-BNC adapters.
Most remarkable is the slow speed of light in vacuum in the USA ;-)
Albert --
Richard Knoppow
dickburk@...
WB6KBL
The document says: "The speed of light in a vacuum is 224844343.5 m/Sec=
0.2248m/nSec. "
I guess Dennis already used some kind of velocity factor here. But this
makes his following derivation invalid:
"The Velocity Factor (the speed the signal travels in the dielectric of
this cable) is VF = 2* 36.0in * 0.0254m/in * 4.4475nSec/m/9.0nSec ~
0.90. "
Albert -- Dennis Tillman W7PF TekScopes Moderator
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Re: My TDR Evaluation of the SG503 012-0482-00 Cable has been uploaded
Hi to All,
Around the mid of 2013 their was a comparable discussion of this cable on:
Now only accessible for Members. Nevertheless clues of it are still on:
And this "replacement" cable is still for sale.
Greetings,
Egge Siert
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Shaun M
Michael A. Terrell
Mlynch001