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Author Topic: Test Equipment: Oscillocopes  (Read 57391 times)

Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #255 on: March 14, 2015, 03:48:33 PM »
For decent coax and sinewaves:  20MHz*meters will be OK.  IE if you have a 10MHz signal a 2 meter unterminated coax won't cause much distortion from the reflections.  For squarewaves, 0.4ns/cm = 1ns/inch rise or fall times will be reasonably clean.  Modern logic like DDR3 has rise and fall times down to around 50ps - 70ps which demands termination in almost all applications.  Stuff like common CMOS logic is much slower and can go a couple to several inches without termination cleanly.

MarkE -
So if I want to test the max output of my oscillator (50Mhz), I should use the shortest possible coax direct into my scope (I do not have any in-line attenuators yet), preferably around 15.6 inches or less? (Just a guess here, but preferably I would use a tee connection with one side going directly into a 50ohm terminator and a 10:1 or 20:1 attenuator between the tee and the scope, so I don't have to max out my time/div to .05us .  Am I correct?)   
What you are stating with square wave with fast rise/fall times applies when I am using a direct connection to scope and not a probe?

Once I actually receive at least the terminations, and make some decent patch cables, I will experiment further with these setups and compare probe use to direct connections with the PC signal generator and the oscillator.  Should I find a pair of, or at least one 20:1 attenuator as well, or is that not necessary for the time being?

TK (and all),

What are your thoughts on this GR974 - BNC adapter?
http://www.ebay.com/itm/BNC-TO-GR874-COAXIAL-CONNECTORS-WITH-16-BELDEN-WIRE-RG58A-U-/291176479245?pt=LH_DefaultDomain_0&hash=item43cb787a0d

I personally do not like the crimp connection at the BNC, but the main thing here is just getting a GR874 connector. I can always replace the BNC fitting, shorten the cable, or possibly even replace the RG-58 cable with something better if it becomes necessary at some point.  I would rather get a GR to BNC direct one piece, but everyone is wanting upwards of $30 for a single unit..

Free Energy | searching for free energy and discussing free energy

Re: Test Equipment: Oscillocopes
« Reply #255 on: March 14, 2015, 03:48:33 PM »

Offline MarkE

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Re: Test Equipment: Oscillocopes
« Reply #256 on: March 14, 2015, 04:29:03 PM »
MarkE -
So if I want to test the max output of my oscillator (50Mhz), I should use the shortest possible coax direct into my scope (I do not have any in-line attenuators yet), preferably around 15.6 inches or less? (Just a guess here, but preferably I would use a tee connection with one side going directly into a 50ohm terminator and a 10:1 or 20:1 attenuator between the tee and the scope, so I don't have to max out my time/div to .05us .  Am I correct?)   
What you are stating with square wave with fast rise/fall times applies when I am using a direct connection to scope and not a probe?
For sinewaves the signal is narrow band and we can talk about the signal frequency.  Yes, if you do not want to see significant distortion from an unterminated 50MHz signal then you don't want a propagation path longer than about 1/10th the period: 1/10th * 20ns = 2ns ~1.25' or about 15 inches.  It is not as though at 15.1" you will have a problem.  But you will get a very rude surprise at a quarter wavelength.

Things won't be too bad using a BNC T right at the scope that has a 50 Ohm terminator on one leg.
Quote

Once I actually receive at least the terminations, and make some decent patch cables, I will experiment further with these setups and compare probe use to direct connections with the PC signal generator and the oscillator.  Should I find a pair of, or at least one 20:1 attenuator as well, or is that not necessary for the time being?
Attenuators have limited usefulness.  They can be useful for limiting reflections.  Your 465 limits you to 100MHz, so I don't think reflections are going to be your biggest headaches.  Sometimes a 2:1 power divider is a handy thing to have around.  With one of those you can fire off a signal to a DUT and monitor the original signal on your scope without distorting it.
Quote

TK (and all),

What are your thoughts on this GR974 - BNC adapter?
http://www.ebay.com/itm/BNC-TO-GR874-COAXIAL-CONNECTORS-WITH-16-BELDEN-WIRE-RG58A-U-/291176479245?pt=LH_DefaultDomain_0&hash=item43cb787a0d

I personally do not like the crimp connection at the BNC, but the main thing here is just getting a GR874 connector. I can always replace the BNC fitting, shorten the cable, or possibly even replace the RG-58 cable with something better if it becomes necessary at some point.  I would rather get a GR to BNC direct one piece, but everyone is wanting upwards of $30 for a single unit..
With shipping this used unit is going to cost you $15.00  It looks serviceable.

Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #257 on: March 14, 2015, 09:20:58 PM »
@Brian:

This should be a suitable replacement for your panel mount 874 connector:
http://www.ebay.com/itm/GENERAL-RADIO-GR-874-PB58-CONNECTOR-NEW-/121589661784?pt=LH_DefaultDomain_0&hash=item1c4f4f0058

This place has a bunch of 874 fittings, etc but I didn't see the precise panel mount connector listed, you may want to call them to see if they have the exact replacement:
http://www.mgs4u.com/RF-Microwave/General-Radio-GR-874.htm

If I were you I'd stick to 50 ohm co-ax and the BNC connector system for all Ts, terminators, attenuators, patch cords and other fittings, and just get the one necessary 874-to-BNC adaptor for the GenRad oscillator itself.

Free Energy | searching for free energy and discussing free energy

Re: Test Equipment: Oscillocopes
« Reply #257 on: March 14, 2015, 09:20:58 PM »
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Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #258 on: March 14, 2015, 11:14:03 PM »
@Brian:

This should be a suitable replacement for your panel mount 874 connector:
http://www.ebay.com/itm/GENERAL-RADIO-GR-874-PB58-CONNECTOR-NEW-/121589661784?pt=LH_DefaultDomain_0&hash=item1c4f4f0058

Yep, that's the exact one that the manual specifies as it's "Panel Mount Connector".  I did not see that listing when I first searched.

Quote
If I were you I'd stick to 50 ohm co-ax and the BNC connector system for all Ts, terminators, attenuators, patch cords and other fittings, and just get the one necessary 874-to-BNC adaptor for the GenRad oscillator itself.

That is the plan.  When I said "Replace the BNC connector" I meant replacing the crimp-on BNC with a Solder-type or Compression-type BNC fitting.  From my experience with cable and satellite systems, crimping, crushing, or even sometimes squeezing a coax cable can cause distortion to the signal. This occurs mostly with digital signals, but just the fact that it can distort a signal at all makes me not want crimp fittings for anything. Not only that, but they aren't very secure. One good yank and the connector could come right off. 
As for the 'making my own patch cables' - the only reason I am planning on doing this for the time being is that I have a surplus of compression BNC fittings, the coax strippers, and compression tool to do it all. I have thousands of feet of RG6 that I can't use, but RG58 is pretty cheap. I could make 12 2' cables for the cost of one actual patch cable, plus I can make them custom length so I don't have a bunch of excess rolled up.  If I had to buy everything, I would just buy a couple pairs of cables instead.

I was playing with my Arduino a little earlier in preparation to build that Inducto-meter.  I built the I2C LCD interface and found out that the coding in the sketch is apparently incorrect... and I have no idea how to fix it.  So I guess until I learn how to write code for it, or someone else fixes it, I will be using the multiple wire LCD setup. I did notice that with that specific IC I can run up to 8 LCD's off of the same two wires by just assigning different addresses.  I'm assuming I could easily add a piezo instead of one of the other screens.  That would bring me up to the Parallax's capabilities for much cheaper than $45. I'll figure out the coding issue in the next few days hopefully. 

Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #259 on: April 11, 2015, 01:56:32 AM »
Well, well, well.....  It appears that Mr Tek decided to start acting up again....
Everything has been fine and dandy up until today, when Channel 2 decided it didn't want to trigger above the .2V/div (on 1x, 2V/div 10x) setting.
I have been using it a bit probing around on various circuits, and never had any problems at all, until I got this FG today and started testing it out.

This is where things went wrong:
At first, I was comparing the MAIN output (on CH1 scope) to the TTL output (CH2 scope) for a while, and playing with the sweep settings on the Tek CFG253.  At this point everything was fine.
Next I disconnected from the Tek and connected up to the Wavetek 166.  I tested it out a bit on only channel one for a while, and then hooked up TTL to channel 2 of my scope, and that is when I noticed something was wrong with Channel 2.  I then disconnected everything, went back to the Tek 253 and hooked up the MAIN to CH1 and got it displaying a waveform.  I set CH2 of the scope to the exact same settings (above .2V/div) and switched my BNC from the MAIN of FG to CH2, and could not get it to trigger and display the waveform.  When I put it on AUTO I get a nearly flatlined trace, and cannot get a stable trigger at all.    :(

I could just leave it like this, and only be able to use CH2 for up to 16V max with a 10X probe, but who wants to have a piece of equipment that they can't use the full range of features on??  Not me!   If I can't solve this, it's going to drive me nuts!    I'm going to look thru the troubleshooting and schematics of the manual and see what I can figure out here after I make a video to show what's happening.  For now I really just wanted to get this info out here to see if anyone has any ideas that can help me get a bead on what's wrong here.

A video demonstrating the problem using a small device and also a function generator:
https://www.youtube.com/watch?v=YGbAhnIFfeU

Thank you for all of your help everyone!   You've all gotten me this far in such a short amount of time, which is incredible.  Hopefully this problem can be resolved fairly easily and the full functionality of this scope restored.

Free Energy | searching for free energy and discussing free energy

Re: Test Equipment: Oscillocopes
« Reply #259 on: April 11, 2015, 01:56:32 AM »
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Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #260 on: April 11, 2015, 02:44:36 AM »
Wellllll,
I am looking at the schematic for the CH2 vertical preamp and my assessment is that the X100 attenuator is blown.   I don't know how I did it, but I must have.  I am attaching a picture of the internal settings for the CH2 V/div knob, and you will notice that above 500mV/div and above use the X100 attenuator. nothing below that does.  This makes perfect sense, now just to find the part.      I'm almost 100% certain that this is it, so if anyone would be able to confirm this for me, I'll just order the part instead of even opening up the scope and looking around in it.

Offline Brian516

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For future reference - the solution to the problem
« Reply #261 on: April 16, 2015, 12:08:24 AM »
I am just going to post this for future reference for anyone who may end up having the same problem.

I correctly diagnosed the problem I was having with channel 2 above 200mV/div - It was in fact the X100 attenuator, and replacing that part did fix the problem.
I am thinking that this may have been the faulty part that was spoken of when I acquired the scope, and it had just enough life left in it to get me thus far on a good cleaning before blowing. (since after doing some researching on no-no's with Scopes, I have found none that I may have done).   

Also, since I still had "noise" from my vertical position knobs after my previous cleaning attempts (especially channel 2), I decided I would take care of that while I had it opened up.
- I loosened the 4 screws on the back of the pot case just enough to be able to shoot some LPS inside of it.  I gave it a shot, worked the pot back and forth a few times, then gave it another rinsing shot, and tightened the screws back up.   This solved that problem entirely.  Now when I adjust the vertical position, even if I turn the knob quickly, I don't get a bunch of scratchy lines across my CRT.   ::thumbs up::

That is all...

Free Energy | searching for free energy and discussing free energy

For future reference - the solution to the problem
« Reply #261 on: April 16, 2015, 12:08:24 AM »
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Offline Pirate88179

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Re: For future reference - the solution to the problem
« Reply #262 on: April 16, 2015, 04:03:56 AM »
I am just going to post this for future reference for anyone who may end up having the same problem.

I correctly diagnosed the problem I was having with channel 2 above 200mV/div - It was in fact the X100 attenuator, and replacing that part did fix the problem.
I am thinking that this may have been the faulty part that was spoken of when I acquired the scope, and it had just enough life left in it to get me thus far on a good cleaning before blowing. (since after doing some researching on no-no's with Scopes, I have found none that I may have done).   

Also, since I still had "noise" from my vertical position knobs after my previous cleaning attempts (especially channel 2), I decided I would take care of that while I had it opened up.
- I loosened the 4 screws on the back of the pot case just enough to be able to shoot some LPS inside of it.  I gave it a shot, worked the pot back and forth a few times, then gave it another rinsing shot, and tightened the screws back up.   This solved that problem entirely.  Now when I adjust the vertical position, even if I turn the knob quickly, I don't get a bunch of scratchy lines across my CRT.   ::thumbs up::

That is all...

Good work.

Don't feel bad about having probs with a used scope.  TK just received a brand new 4 channel digital scope and has problems with channel 4 right out of the box.  Of course, his is still under warranty but, what a pain in the ass.

Bill

Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #263 on: April 16, 2015, 04:58:06 AM »
Yep, had to send it back to the vendor, and they've sent me a replacement, due to arrive tomorrow.

Here's the video I made documenting the main problem with the channel 4 :

http://www.youtube.com/watch?v=7RvcByoEE5o

Free Energy | searching for free energy and discussing free energy

Re: Test Equipment: Oscillocopes
« Reply #263 on: April 16, 2015, 04:58:06 AM »
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Offline Brian516

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Re: For future reference - the solution to the problem
« Reply #264 on: April 16, 2015, 07:04:24 AM »
Good work.

Don't feel bad about having probs with a used scope.  TK just received a brand new 4 channel digital scope and has problems with channel 4 right out of the box.  Of course, his is still under warranty but, what a pain in the ass.

Bill

Yes, that is very unfortunate.  Very few, if any companies make anything with the same care and at the same quality level as they used to.  Also, the more functions that are added to something, the more "components" there are to be broken.  (I quoted that since it technically speaking has less actual components due to ICs)  Also, it becomes that much harder to repair since so many things are packed onto a single semiconductor device.
      This is why I have been tossing around the idea of buying a used, time-tested digitizing or digital phosphor oscilloscope.... but then again, if I were to buy new and had an issue, I could just send it in under warranty, and buy an extended-extended warranty.

Considering the point I am at in my electronic education, I think it's better if I don't have a scope that does all the math for me.... A freq counter, pencil & paper, and my brain need their workout!!

TK - Let's all hope that they send a delivery driver that can pick the correct house this time - or that they reamed the idjjot and he doesn't make the same mistake twice.  I'm sure you'll be doing what I'd do, and continually check the tracking status!  haha     Let's PRAY that this scope doesn't have ANY issues at all this time! Or ever, for that matter!

Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #265 on: April 16, 2015, 06:01:38 PM »
Yep, it supposedly is on the local brown truck for delivery today --- sometime today. The last one was dropped off around 7:30 pm, at the wrong house next door.
I spray-painted our house number on a big piece of cardboard and put it on the front porch.... maybe that will help the driver get oriented...

I'm watching the front-porch security cam on the computer, watching for the Brown Truck... yesterday I saw them about 6 times driving past on the street, haven't seen any yet today. I'm afraid to go make lunch, might miss something while I'm in the kitchen.

Free Energy | searching for free energy and discussing free energy

Re: Test Equipment: Oscillocopes
« Reply #265 on: April 16, 2015, 06:01:38 PM »
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Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #266 on: April 16, 2015, 07:25:18 PM »
I don't blame you.   On the days that I was expecting an equipment delivery I actually stayed home just to make sure I was there to get it as soon as it arrived, and I kept checking for it outside and constantly reloading the tracking page....   and I will be doing this again on Sat or Mon for my freq counter.  I live directly off of a high traffic state road, though, so it's doubtful anyone would be bold enough to steal something off my front porch or garage door. Ya never know, though.   I'd be even more anxious if I were waiting on something like your scope! 

Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #267 on: April 16, 2015, 07:27:38 PM »
What frequency counter did you wind up getting?

Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #268 on: April 16, 2015, 09:14:56 PM »
Tektronix CMC251.  1hz - 1.3Ghz w/ precision 10Mhz reference oscillator (and self-check function).  :)
   I don't know if it has the Ratio A/B function, but it appears to be very close to mint condition like the CFG253, it's from the same seller, and I got quite a deal on it.  I d/l'ed the Manual, but still didn't catch anything on Ratio, but didn't fully go thru it yet.
   I think the ones they had donated to them like these Tek's may have been some university's property that were tucked away somewhere as spares.  The top of the CFG253 had sharpie on it of some stock-type designation number, there is zero wear on it, but a few of the push in-out type selector buttons have a whiter area on top from where they had been left pushed in for such a long time. They are evenly toned, which leads me to my conclusion of university back-stock - rarely - if ever used prior to initial testing. 
   I've got my fingers crossed that the counter is the exact same.   :)

It's a TCXO not an OCXO, but it's probably the closest I'll get to super-ultra precision for under $100 and in (hopefully) fantastic condition.

Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #269 on: April 16, 2015, 11:28:15 PM »
Good find, sounds like you got a good deal. Unfortunately it does not have Ratio A/B, but it does have Period and Totalizer functions.

Here's what it looks like inside:
http://www.eevblog.com/forum/testgear/tektronix-cmc251-frequency-counter/

 

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