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Author Topic: Test Equipment: Oscillocopes  (Read 67186 times)

Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #135 on: February 24, 2015, 06:58:47 PM »
So what DDS chip would you recommend?  I've read a good bit that more or less said that the best ones to go with are the AD series, particularly AD9914.  Also the 5932, 9833, and 9959...  oh, and also the XR2206. What are your thoughts, MarkE?

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Re: Test Equipment: Oscillocopes
« Reply #135 on: February 24, 2015, 06:58:47 PM »

Offline picowatt

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Re: Test Equipment: Oscillocopes
« Reply #136 on: February 24, 2015, 07:35:33 PM »
Brian,

Your decision regarding what to buy as a signal source is somewhat dependent upon what you want to use your test equipment for.

That said, I'd recommend saving up for a good used FG or buying one of the 2MHz units on Ebay for $60 or so.

For now, if you're just learning to use a 'scope, I would suggest playing with some audio sources.  Simultaneously listening to music while viewing it on your scope gives you a good visualization of what is going on with both.  Although music/audio signals are a bit more complex (and harder to trigger on) than what is produced by an FG, displaying a left/right stereo signal on your scope while listening to your favorite music can be both enjoyable and enlightening with regard to your scope's operation. 

Also, there is sound card FG software out there.  Possibly someone here can recommend a freeware (and a clean download link) that can get you started in that direction.

Even with a FG (or FG software), I would recommend adapting the signal cables as necessary to allow you to listen along as you view various waveforms and frequencies on your scope.

PW

Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #137 on: February 24, 2015, 08:24:05 PM »
You can use the powerful audio editing applications Audacity (linux) or GoldWave (windows) to generate all kinds of audio frequency waveforms to look at, output from your computer's sound card, one or two channels as you like.
Audacity is freeware and so are versions of GoldWave.

And don't forget about the venerable GenRad 1330-A, which covers the RF range from 5 kHz to 50 MHz with a sine wave output that can also be partially modulated by the fixed audio frequencies from the unit's audio oscillator section ( at the higher frequency ranges of the RF signal).

If I had a hundred dollars to spend I'd buy this right now:

http://www.ebay.com/itm/Interstate-IFC-F-74-F74-20Mhz-Sweep-Function-Generator-/301529989757

Note the back panel Signal Ground isolation switch... this can be a very helpful thing to have in a function generator.


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Re: Test Equipment: Oscillocopes
« Reply #137 on: February 24, 2015, 08:24:05 PM »
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Offline Vortex1

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Re: Test Equipment: Oscillocopes
« Reply #138 on: February 24, 2015, 08:58:01 PM »
Quote
Also, there is sound card FG software out there.  Possibly someone here can recommend a freeware (and a clean download link) that can get you started in that direction.

I recommend this PC based O'scope and sig gen combo software for the beginner.

Many features including sweeps of audio, spectrum, etc

http://www.zeitnitz.eu/scope_en

There are other good ones out there, I just happen to like this one.

Do build a limiter protection box for your soundcard.

Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #139 on: February 24, 2015, 09:09:05 PM »
I recommend this PC based O'scope and sig gen combo software for the beginner.

Many features including sweeps of audio, spectrum, etc

http://www.zeitnitz.eu/scope_en

There are other good ones out there, I just happen to like this one.

Do build a limiter protection box for your soundcard.

Are you using a sound-card based oscilloscope for your waveforms that you posted earlier? I have encountered several cases where PC-soundcards actually inverted one or both of the inputs when used with scope software, with no indication other than the flipped phase of the displayed signals themselves.

Free Energy | searching for free energy and discussing free energy

Re: Test Equipment: Oscillocopes
« Reply #139 on: February 24, 2015, 09:09:05 PM »
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Offline MarkE

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Re: Test Equipment: Oscillocopes
« Reply #140 on: February 24, 2015, 09:14:37 PM »
So what DDS chip would you recommend?  I've read a good bit that more or less said that the best ones to go with are the AD series, particularly AD9914.  Also the 5932, 9833, and 9959...  oh, and also the XR2206. What are your thoughts, MarkE?
I f I were going to build something I like the AD9857 because it is 14 bits.  But there is lots of stuff that you can buy that is cheaper than the one chip alone.  $20. gets you something like Pirate Bill found and $60. gets you something that is packaged in a half way decent case that does 5MHz.

Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #141 on: February 24, 2015, 09:31:30 PM »
Quote
That said, I'd recommend saving up for a good used FG or buying one of the 2MHz units on Ebay for $60 or so.

PW,
That goes right along with what I was just thinking about asking - If, being at the stage I am at, it would be reasonable to buy a DDS chip and build a FG, and if I would be able to obtain comparable features and same or better signal quality.   Sometimes when I think of something, I immediately dive in the deep end as far as ideas/plans go, and then as a few hours or so goes by, I think a little more into whether I'm being reasonable or not. Most of the time, it's not.

Quote
You can use the powerful audio editing applications Audacity (linux) or GoldWave (windows) to generate all kinds of audio frequency waveforms to look at, output from your computer's sound card, one or two channels as you like.
Audacity is freeware and so are versions of GoldWave.

And don't forget about the venerable GenRad 1330-A, which covers the RF range from 5 kHz to 50 MHz with a sine wave output that can also be partially modulated by the fixed audio frequencies from the unit's audio oscillator section ( at the higher frequency ranges of the RF signal).

If I had a hundred dollars to spend I'd buy this right now:

http://www.ebay.com/itm/Interstate-IFC-F-74-F74-20Mhz-Sweep-Function-Generator-/301529989757

I'll have to go to storage and dig out my old Dell dimension 8250 and get it up and running with Linux, and download some software on it.  I don't feel like buying any cheap-o USB sound cards, and I have 4 or 5 good 5.1 sound cards in storage I can use.  I did read up on sound card based FG's a little bit, and got the jist that I will most definitely be needing to build a limiter unit so I don't fry them up crispy. I don't know if that PC will support installing more than one sound card, but it would be pretty nifty if I could install two, run a PC scope on one, and FG on the other, or have several FG/scope channels.     I know I already have a real scope and everything, but there should be some math/charting features along with other digital scope features on the PC based scope.   But instead of using a cheap 3.5mm home-made probe for it, maybe I can build a little BNC interface box - or if I can get that dongle, maybe I can make something with that.  or even the arduino.  I'm probably getting a little bit ahead of myself here though.  Just some ideas. 
I'll just start with the sound card FG, though.
Hopefully some of my stuff on ebay sells soon, and then maybe I can scoop up that FG you linked to before it's gone...

Quote
I recommend this PC based O'scope and sig gen combo software for the beginner.
Many features including sweeps of audio, spectrum, etc
http://www.zeitnitz.eu/scope_en
There are other good ones out there, I just happen to like this one.
Do build a limiter protection box for your soundcard.

Vortex -
That definitely seems like a good one to start with once I get my desktop out of storage.  I'm running out of room to put all of this stuff!  Going to have to do some re-organizing and add some more shelves to my ikea wall unit...


Brian

Free Energy | searching for free energy and discussing free energy

Re: Test Equipment: Oscillocopes
« Reply #141 on: February 24, 2015, 09:31:30 PM »
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Offline picowatt

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Re: Test Equipment: Oscillocopes
« Reply #142 on: February 24, 2015, 09:35:22 PM »
Brian,

Why would you need a dedicated computer or two sound cards to start using a software based FG and your scope?

What are you posting on this forum with?

PW

Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #143 on: February 24, 2015, 11:47:49 PM »
Brian,

Why would you need a dedicated computer or two sound cards to start using a software based FG and your scope?

What are you posting on this forum with?

PW

My laptop, and as far as sound card goes, all it has is a combo jack. Now that you've asked...
What is the real difference between using FG software out the headphone jack to a modified cable and a FG off of a dedicated sound card?
Is it really only the PC based scope that needs a dedicated sound card??  I'm confused.  going to have to do a search and read a few articles again..
I have FG software. There is an FG built into Visual Analyzer, and "Function Generator" by Cognaxon. From what I remember, the only issue with using PC based FG's is the amplification. Is this correct? (That is, amplification for using the FG for more than just running it to the scope, I'm sure using it without amplification is fine for only that aspect. Maybe this is where I am confusing people.....)
I may have confused some of you when speaking of this, because I was referring to having a PC based FG and possibly scope w/ extras for future projects as well.   Sorry.... I need to just stick to talking about specifically using it for learning functions on the scope.   My fault...

Brian

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Re: Test Equipment: Oscillocopes
« Reply #143 on: February 24, 2015, 11:47:49 PM »
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Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #144 on: February 25, 2015, 12:08:50 AM »
Ok, so what I have done here is this:
I have a standard 3.5mm stereo audio cable ran to a jack that I pulled off a board.  I figured out what was left, right, and ground, and soldered red, white, black to it.  I'm about to connect another jack into the setup so I can listen in to the signal.
Do I need to be on AC or DC? This is what I am unsure of as far as when I connect to something... what qualifies for an AC signal and what qualifies as DC? and what do I use ground for? Is that ground setting also to be referred to as "reference"? meaning that, on that setting, I would be seeing what my AC or DC signal would be in reference to?

Also, I would only need a limiter protection box if I were running my signal to an amp and/or using it for anything other than putting the signal to the scope, right?

Brian

Offline TinselKoala

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Re: Test Equipment: Oscillocopes
« Reply #145 on: February 25, 2015, 12:43:36 AM »
That little switch under the channel vertical V/div setting knob is the most misunderstood scope control ever, and is a particular "pet peeve" of mine.

This is the channel's _input coupling_ switch.
AC -Ground-DC.

It does NOT refer to the "type of signal" that you are measuring! It refers to how the signal is _coupled_ into the oscilloscope.

The "ground" setting is, or should be, obvious. It disconnects the probe _tip_ from the scope and connects the input circuitry directly to the scope's chassis ground. This means that the scope's input sees "zero volts". No signal. So you select this when you want to set the channel's baseline, or zero voltage display, on some reference marker on the screen, like the center graticule line or some other graticule line of your choosing using the vertical position control. It essentially turns that channel's input off, removes the signal from the probe, connects the scope's input to ground (and leaves the probe tip floating so it doesn't short-circuit the device under test.)

The "DC" setting is called "DC Coupling". I believe it should more properly just be called "Direct Coupling", since that is what it does: It connects the probe tip _directly_ to the scope's input circuitry. Just that. (Here I'm disregarding the input and probe impedances or 10x voltage divider, which are irrelevant to this discussion.)

The "AC" setting is the one that causes confusion. This is "AC Coupling".... the switch simply puts a capacitor in series with the scope probe tip. Just that. This is a "high pass filter" arrangement that works to filter out, or eliminate, a DC component to the signal (the very slowly changing or unchanging part) and only allows the rapidly changing part of the signal to pass through to the scope's input circuitry.

The "AC coupled" setting has two major effects on what you see on the screen.

First, it removes the DC component of an oscillating signal. So, if you are interested in seeing the small oscillating ripple riding on top of a larger DC signal.... this is what you would use to view it. For example, say you have a ripple of 20 mV sitting on top of your +55 V DC power supply. How do you display such a thing? If Direct Coupled, and you use a V/div value that keeps the 55 V on the screen, the ripple is so small compared to that, you'll never see it accurately. So you need to _remove_ that +55 volts DC from the signal and magnify the 20mV ripple so that you can see it displayed at sufficient resolution to measure it. You select "AC Coupled", and then you can turn the V/div setting to some low value like 10mV/div and the ripple will be displayed rippling around the zero baseline level (that you positioned with the "ground" setting) at a good magnification. So in this case even though you are looking at a mostly DC signal, the AC-coupled setting is the appropriate one to use to view the ripple. You use DC-coupled to see the overall voltage level, and AC-coupled to see the tiny ripple on top.

Second, the AC-coupled setting takes the _average_ of the displayed signal and moves it up or down to the channel's zero baseline level that you set using the "ground" switch setting and the vertical position control. Obviously, you then lose the absolute voltage values of the signal when this happens. Peak-to-Peak value remains the same and is accurate, but you no longer know what the actual _peak_ values are because the trace has been moved down or up by some unknown amount to place the _average_ on the zero baseline. So even if you are measuring a truly "AC" signal, if it is not symmetrical about the zero value, the scope will make it _look_ like it is, and sometimes this will be false.

All scopes, whether the latest digital one with all bells and whistles, or an ancient analog clunker, accomplish this miracle in the same way: they simply place a capacitor in series with the probe when "AC-coupled" is selected. Analog scopes do this with a simple switch, digital ones use a software-controlled relay.

Most of the time you will use the DC-coupled setting for almost everything you do with the scope, whether measuring "AC" or "DC" signals. The most often-used reason for using the AC-coupled setting is what I mentioned above: Viewing small ripples on top of larger DC offset signals.



That Interstate F74 sweep FG that I linked earlier is a _good buy_ at 100 dollars. It has functionality that you will not find on many modern FGs for three or four times the price. 20 MHz range, a relatively fast pulse generator feature, a high-amplitude output, the sweep function, ability to float the signal ground, etc. The only drawback to these old Interstate models is the frequency setting knob. It is a vernier control, but it is still a little hard to set a precise frequency on it. I generally run my F43 into a hardware frequency counter when I need to set a precise frequency and this pretty much solves that problem. It is also kind of hard to find manuals for the Interstate line. But they are constructed with the same "generation" of technology as your 465 scope: mostly discrete components, only a few ICs on a robust double-sided circuit board with plenty of room to work.

Free Energy | searching for free energy and discussing free energy

Re: Test Equipment: Oscillocopes
« Reply #145 on: February 25, 2015, 12:43:36 AM »
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Offline Vortex1

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Re: Test Equipment: Oscillocopes
« Reply #146 on: February 25, 2015, 12:50:47 AM »
No separate soundcard is needed. Just use the existing soundcard in the pc.

Stereo line or headphone out is the 2 channel FG output. Stereo line in is the 2 channel scope input.

This applies to the PC based scope I referenced earlier.

I don't know if this software supports a separate dedicated soundcard. A manual is available, it mjght address that issue.

Offline MarkE

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Re: Test Equipment: Oscillocopes
« Reply #147 on: February 25, 2015, 01:59:04 AM »
Ok, so what I have done here is this:
I have a standard 3.5mm stereo audio cable ran to a jack that I pulled off a board.  I figured out what was left, right, and ground, and soldered red, white, black to it.  I'm about to connect another jack into the setup so I can listen in to the signal.
Do I need to be on AC or DC? This is what I am unsure of as far as when I connect to something... what qualifies for an AC signal and what qualifies as DC? and what do I use ground for? Is that ground setting also to be referred to as "reference"? meaning that, on that setting, I would be seeing what my AC or DC signal would be in reference to?

Also, I would only need a limiter protection box if I were running my signal to an amp and/or using it for anything other than putting the signal to the scope, right?

Brian
AC coupling inserts a series capacitor between the signal that you are measuring and the vertical amplifier.  This applies a controlled amount of distortion to the measured signal that:

Removes all DC information.
Attenuates AC information in varying degrees as the frequency falls below about 1/(CCOUPLING*1E6) or typically about 1% attenuation at 40Hz, and shifts the phase of the measured signal beginning below about 40Hz.

AC coupling is useful when:  There is a large and stable DC offset on a signal, and there is little or no content between DC and at least ~40Hz or higher.  For example:  If you want to see the ripple on top of a power supply rail, then AC coupling lets you crank up the gain and see that ripple.

AC coupling is of course useless for DC signals, or signals where the DC content matters (power measurements for instance), or where there is signal content that matters between DC and ~40Hz.

Scope settings for novices:

Probe set to 10X.
Input set to DC.
Gain set to display the entire signal on the display, including the extent of any spikes.
Persistance set to OFF
Averaging set to OFF
20MHz filter set to OFF
Trigger mode set to AUTO
Trigger coupling set to DC
Trigger level autoset to 50% once signal is connected(Tektronix scope feature, may not be available on other brands)
Trigger position set to 0 (Tektronix scope feature, may not be available on other brands)
Change trigger mode from AUTO to NORMAL


Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #148 on: February 25, 2015, 02:46:53 AM »
TK, MarkE,

Thanks for the clarification.  I am going to mentally tag them "Direct" and "Average" so as to remember that DC is for Directly measuring the actual signal, and AC zeroes out the Average signal in order to show the ripple.
This is all starting to come together and make sense to me now. I'll know how to use this scope in almost no time at all! :)   It even seems like a good place to start with scopes in general, since the digital ones have sooo many more functions I will need to learn when I one day scoop one up.  This one will do just fine for quite a while.

Vortex,

Thanks for pointing me to that program. Seems like a decent all around FG/scope when it comes to free stuff.  I have a mono mic input on my combo jack so I would only be able to use 1 channel, but for now I'll only be using the FG part since I already have this 465 to figure out.


I would also just like to note that putting the case back on the scope made a HUGE difference on the stability of the trace and functionality of the controls. I would never have imagined that something as simple as that would have such a big impact.  They really designed these scopes down to the tiniest detail, didn't they??

Brian

Offline Brian516

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Re: Test Equipment: Oscillocopes
« Reply #149 on: February 25, 2015, 04:10:21 AM »
Went to check the compensation on the new probes and the old probes, and noticed that the waveform I am seeing differs a little from the one depicted in the old scope manuals.  Just want to make sure that is what it should look like, so I uploaded another vid. I went thru various settings with the direct lines still hooked up to get the hang of things, and am now checking the probes and then putting some signals from the FG into it to see what I get.  Getting pretty tired so I'll probably save a bit of the good stuff for tomorrow.
I noticed a little issue on the ALT setting with it not wanting to show the CH1 waveform in it's full width on the top section of the screen, and did the same with CH2 on top, and it seemed that adjusting the B trigger level made it a little better.  I decided that I would try it again with the probes instead of direct links and see what happens. If I'm still having issues with it and can't figure it out tomorrow, I'll shoot another vid to show you all what's going on. Hopefully it's nothing, though.

https://www.youtube.com/watch?v=FDZ2ZhdMle4

Brian

 

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