Date   

Re: My TDR Evaluation of the SG503 012-0482-00 Cable has been uploaded

Reginald Beardsley
 

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:

https://www.eevblog.com/forum/beginners/oscilloskope-50ohm-input/msg2351448/#msg2351448

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


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

-----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 50Ω cable, and a Pomona Electronics 50Ω cable.

It is located at:

https://groups.io/g/TekScopes/files/Evaluation%20of%20the%20Tektronix%20
012-
0482-00%20cable%20for%20the%20SG503.pdf

Dennis Tillman W7PF


--
Dennis Tillman W7PF
TekScopes Moderator


Re: My TDR Evaluation of the SG503 012-0482-00 Cable has been uploaded

Siggi
 

On Mon, Apr 29, 2019 at 1:40 PM Dennis Tillman W7PF <dennis@ridesoft.com>
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 :).


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

-----Original Message-----
From: TekScopes@groups.io [mailto:TekScopes@groups.io] 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:

https://groups.io/g/TekScopes/files/Evaluation%20of%20the%20Tektronix
%20012-

0482-00%20cable%20for%20the%20SG503.pdf


Dennis Tillman W7PF



--
Dennis Tillman W7PF
TekScopes Moderator


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

-----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@ix.netcom.com
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


Re: My TDR Evaluation of the SG503 012-0482-00 Cable has been uploaded

Egge Siert
 

Hi to All,

Around the mid of 2013 their was a comparable discussion of this cable on:

http://www.amplifier.cd/smf/index.php?topic=359.0

Now only accessible for Members. Nevertheless clues of it are still on:

https://www.amplifier.cd/Test_Equipment/Tektronix/Tektronix_500/SG503.htm

And this "replacement" cable is still for sale.

https://www.ebay.de/itm/151280227415?ViewItem=&;item=151280227415

Greetings,

Egge Siert


Re: My TDR Evaluation of the SG503 012-0482-00 Cable has been uploaded

Richard Knoppow
 

I know that. I was pointing out that the velocity of propagation in a cable is not the same as in space and that it depends on the physical nature of the cable, including its dielectric constant but you are right that it's mostly the dielectric constant of the core.
the OP was as

On 4/29/2019 9:49 AM, Dennis Tillman W7PF wrote:
Hi Richard,
The speed in a cable is mostly a function of the Dielectric Constant of the filling between the inner conductor and the outer shield.
The dielectric constant of the filling along with the diameter of the inner wire and the distance to the outer shield determines the impedance.
But there are many, many other considerations manufacturers have to consider. Many of those are not listed here. What is here is signal attenuation, how well shielded from interference. Other things to consider are triboelectric noise from flexing the braided shield if the cable will be carrying very small signals, group velocity, cutoff frequency, maximum power it can handle, and on and on. Take a look at this web page to get an idea of what factors are taken into account in design of a coax cable:
http://www2.rfsworld.com/RFS_Edition4/pdfs/TechInfo_Edition4_639-672.pdf
Dennis Tillman W7PF

-----Original Message-----
From: Richard Knoppow
Sent: Monday, April 29, 2019 1:50 AM
Subject: Re: [TekScopes] My TDR Evaluation of the SG503 012-0482-00
Cable has been uploaded

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@ix.netcom.com
WB6KBL
--
Richard Knoppow
dickburk@ix.netcom.com
WB6KBL


Re: My TDR Evaluation of the SG503 012-0482-00 Cable has been uploaded

Merchison Burke
 

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:

https://groups.io/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.
https://www.avg.com


Re: My TDR Evaluation of the SG503 012-0482-00 Cable has been uploaded

 

Hi Richard,
The speed in a cable is mostly a function of the Dielectric Constant of the filling between the inner conductor and the outer shield.
The dielectric constant of the filling along with the diameter of the inner wire and the distance to the outer shield determines the impedance.

But there are many, many other considerations manufacturers have to consider. Many of those are not listed here. What is here is signal attenuation, how well shielded from interference. Other things to consider are triboelectric noise from flexing the braided shield if the cable will be carrying very small signals, group velocity, cutoff frequency, maximum power it can handle, and on and on. Take a look at this web page to get an idea of what factors are taken into account in design of a coax cable:
http://www2.rfsworld.com/RFS_Edition4/pdfs/TechInfo_Edition4_639-672.pdf

Dennis Tillman W7PF

-----Original Message-----
From: Richard Knoppow
Sent: Monday, April 29, 2019 1:50 AM
Subject: Re: [TekScopes] My TDR Evaluation of the SG503 012-0482-00
Cable has been uploaded

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@ix.netcom.com
WB6KBL



--
Dennis Tillman W7PF
TekScopes Moderator


Re: My TDR Evaluation of the SG503 012-0482-00 Cable has been uploaded

 

Hi Tom,

Wikipedia is your friend when it comes to Velocity Factors. Scroll down this
web page
https://en.wikipedia.org/wiki/Coaxial_cable

Or in your web browser type "wikipedia coax" and it is usually the first hit
you get.

Wikipedia lists about 40 or 50 types of cable with all their parameters
including velocity factors.
It is my favorite, quickest way to find any information about different coax
cables.

Dennis Tillman W7PF

-----Original Message-----
From: Tom Gardner
Sent: Monday, April 29, 2019 1:03 AM
Subject: Re: [TekScopes] My TDR Evaluation of the SG503 012-0482-00
Cable has been uploaded

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 50Ω cable, and a Pomona Electronics 50Ω cable.

It is located at:

https://groups.io/g/TekScopes/files/Evaluation%20of%20the%20Tektronix%
20012- 0482-00%20cable%20for%20the%20SG503.pdf

Dennis Tillman W7PF



--
Dennis Tillman W7PF
TekScopes Moderator


Re: 2465B Parametric Freq Measurement Error

Chuck Harris
 

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




Re: 475A with High +110 rail

Dave Hills
 

With 134v on Q1496 collector, you should see +61v at Q1490's base. This will completely shut down the regulator by reverse biasing Q1494 b-e. That said it only leaves R1483, Q1496, CR1498, and R1488 as likely suspects. R1483 would have to have drifted VERY low, (unlikely), or R1488 VERY high, (possible, but not likely to cause these symptoms), leaving a leaky or shorted Q1496 or CR1489. Note that an OPEN CR1489 would likely cause Q1496 to subsequently fail. Also, check that CR1489 has not been installed backward.

Please forgive the caps, not shouting, just no other way to highlight for emphasis.

Dave


Re: 2465B Parametric Freq Measurement Error

John Ferguson
 

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


2465 repair attempt with (horizontal?) issues, help needed

satbeginner
 

Hi all,

I got (yet another for my collection) 2465, it was stated it had problems before I got it, so no problem there.
What have I done so far:

Recapped the Power Supply, cleaned the Siemens fan and powered the scope up.
Power supply is OK, all voltages are well within range in terms of value and ripple, set the reference voltage for 10V.
Control DAC and reference are checked and set for a 2.5V range.

After Power-On I have a straight trace, not really focussed perfectly, but more interesting: I got no proper readout, I have two blurry lines at the top and bottom of the screen.
When I apply a calibration signal from the scope itself when on Auto Lvl the triggered light goes on, but the image looks like if it is not triggered, because I see just two horizontal lines.
They seem to be the high and low level of the calibration signal.

When I switch on the Voltages cursors they seem OK, a little vague, but the respond to the delta-settings knobs, but when I switch to the vertical (Time Cursors) I see some vague light in the tube as if the beam is hitting the sides?
The trace stays where it is.

Now the weird thing: as I am looking for causes, I tried the following:

When I put the scope on X-Y mode using Ch2 I get a line instead of a dot??
When I check the outputs of the U800 I have clean static DC voltages (cursors and readout switched off) approx. between 20 and 60V, depending on the Ch1 position, so that should be a dot, but it is a horizontal line......????
Vertical position of this line (that should be a dot) is nicely controlled by the Ch2 position.

When not in X-Y mode, the horizontal trace appears to be way to wide as well, so it looks like something other that the U800 is causing a horizontal deflection?

Any ideas where this line / horizontal deflection is coming from?
It's a line, so it should be some changing signal, but now I could use some tips and tricks.

Thank and un saludo,

Leo

I


Re: 2465B Parametric Freq Measurement Error

Tom B
 

Hi Chuck,

Exactly!
Have you tried their product?
Nope. I found others for sale, but these were cheaper.

Tom


-Chuck Harris

Tom B wrote:
Hi Chuck,

I use one of the red plastic nutstarters that would be familiar to old
guys that built Heathkits. I wish I could find them new somewhere,
but
I have enough to last my lifetime of used.
Like this:


Re: 2465B Parametric Freq Measurement Error

Chuck Harris
 

Exactly!

Have you tried their product?

-Chuck Harris

Tom B wrote:

Hi Chuck,

I use one of the red plastic nutstarters that would be familiar to old
guys that built Heathkits. I wish I could find them new somewhere, but
I have enough to last my lifetime of used.
Like this: http://smallbear-electronics.mybigcommerce.com/nut-starter/

Tom





Re: 475A with High +110 rail

tom jobe <tomjobe@...>
 

On the 474A L.V. schematic it shows the expected voltage at the emitter of Q1496 as being 135.6 volts, which is quite close to your 134.66 reading at your +110 test point.
It shows the expected voltage at the +110 test point as being 111 volts with only R1488 and Q1496 directly between the +110 test point and the expected 135.6 volts at the emitter of Q1496.
Maybe you can find the problem by probing around right in that area?
tom jobe...

On 4/28/2019 10:00 PM, Mlynch001 wrote:
I have searched for a previous thread that was referred to in a post about a "high" 110 voltage rail on a 475 from back in 2012. I failed to find that post or any other applicable answer, perhaps I am not searching for the correct words? So I will ask for some help. I have a 475A with DM44 s/n B012228. After a thorough cleaning, I turned it on and find that for the most part it works great, no triggering issues, bright trace, all controls respond as expected, just dirty pots and switches. I supply various signals to the A and B channels and the scope displays a good trace with with amplitude matching the output of my signal generator, so calibration seems to be close enough for hobby work. The scope simply does not act as if there is anything wrong. For safety sake, I pulled the case and tested the various system voltages on the A9 interface voltage test points. I found everything to be spot on, except the +110 volt rail, Voltages as follows:
-15V = -14.998
-8V = -8.005
5V = 5.005
15V = 15.002
50V = 50.035
Unregulated 50V = 63.35
110V = 134.66

Line Voltage is 120V and the voltage calibrator on the transformer is set to the proper voltage. I pulled and tested Q1490, Q1494, Q1496 and Q1497. These all tested "good" with a transistor tester. I also replaced Q1490 and Q1494 with "Known Good" components, with no change noted in the +110V rail. I did not have exact replacements for Q1497 or Q1496, but they did both test good. I did go through to check and seat all the transistors that I could reach on all the boards. I checked the various resistors in LV +110 Supply regulator circuit (the ones I could reach) and found then to be very close to correct. I do not want to start un-soldering components without some idea of what to check next. I do not know if CR1489 has anything to do with the voltage regulation or not, but that component appears to be part of the +110 regulation system. Other than the "too high" +110 rail, the scope demonstrates no other issues, nothing smells "Hot" and no "magic smoke", The boards inside the scope are perfect, no signs of repairs, heat or damage. I just want to sort this out before I use the scope very much. Collector voltage on Q1497 is 134.5 and Q1496 at about 133.8. Almost everything agrees with the schematic EXCEPT that pesky +110V rail. Any ideas where to check next?


Re: 2465B Parametric Freq Measurement Error

Tom B
 

Hi Chuck,

I use one of the red plastic nutstarters that would be familiar to old
guys that built Heathkits. I wish I could find them new somewhere, but
I have enough to last my lifetime of used.
Like this: http://smallbear-electronics.mybigcommerce.com/nut-starter/

Tom


Re: My TDR Evaluation of the SG503 012-0482-00 Cable has been uploaded

Albert Otten
 

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@ix.netcom.com
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


Re: 2465B Parametric Freq Measurement Error

Chuck Harris
 

All members of the 2465 family use interchangeable trigger hybrids.
To remove them, remove the four nuts at the corners of the module.

Tektronix considered them all to be "selected"... which I think meant
they tried them to see if they would work. the "-0X" suffix meant
changes in production usually... stuff like Tek vs Maxtek, or this
or that revision on their fabrication line...

I would suggest that your first attempted fix be to remove the module,
and clean the gold contacts with a Q-tip and IPA.

When you put the module back, seat it with finger pressure, and hold
it there as you finger tighten a pair of nuts on diagonal corners.
Then install the other pair of nuts. Tighten the nuts 1/4 turn past
where they just make contact. The tightness doesn't make or improve
electrical contact, so just 1/4 turn past the nut touching the hybrid
when it is touching the PCB.

I use one of the red plastic nutstarters that would be familiar to old
guys that built Heathkits. I wish I could find them new somewhere, but
I have enough to last my lifetime of used.

If cleaning the existing hybrid's contacts makes no improvement, then
swap in a hybrid from a working scope, and that should fix the problem.

-Chuck Harris

Tony Fleming wrote:

Is my Tektronix 2465 DMS using the same part number or do I need a
different one?
Where would I find more information how to perform the replacement?
Thanks.
Tony

On Sun, Apr 28, 2019 at 8:43 PM Chuck Harris <cfharris@erols.com> wrote:

The parametric measurements use the trigger hybrid extensively,
and their performance is directly related to how well that hybrid
performs. Some are better than others.

-Chuck Harris

joe@reforyou.net wrote:
After successfully calibrating my 2465B, it reports "All tests passed"
on start up. The question marks are all gone! My issue is with the
parametric measurement of frequency. When I attempt to measure the
frequency of a sine wave at frequencies higher than 10 MHz, the scope
reports the frequency as 35.62 kHz. Any test frequency above 10 MHz gets
the exact same report, 35.62 kHz. Below 10 MHz, it reports various
incorrect values (i.e. a 4.89 MHz signal is reported as 6.35 MHz). At
about 500 kHz and lower frequencies, the scope reports the correct
frequency. I have replaced the PAL at U975 - no change. Any suggestions?







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