Hello, I've been trying to learn how to use my new Protek 800 series
hand held Digital Oscilloscope.

So, I connected the single oscilloscope probe to the output of a used
function generator that I bought on EBay.

On oscilloscope auto, what I see is a waveform that I can only
describe as a repeating sinc function. When I increase the frequency
of the sine wave on the generator, I see more and more tiny waves
appear in this sinc-like function. If I increase the amplitude on the
generator I see these tiny waveforms in the sinc-like waves increase
in amplitude.

This seems strange to me because I set the function generator for a
repeating sine wave, but what I see is this repeating sinc-like
waveform. The sinc waveform becomes more and more detailed.

Is the generator bad?

How do I get a repeating sine wave without the sinc?

I set the oscilloscope to auto and the resulting setting are:

20V/div, 200mV/time div
coupling is AC
probe set to 1X
Trigger set to edge and slope set to rising

If I try fooling around with the various setting I cannot improve
things.

Setting trigger to pulse, pattern, or video did not help.

Setting coupling to DC or ground did not help.

If I set the time division very low (micro divisions) to zoom in on my
tiny
sine waves they still seem to want to float around.

What do I do?

Thank you,
Christopher Lusardi

Chris L (c...@aol.com) writes:
> Hello, I've been trying to learn how to use my new Protek 800 series
> hand held Digital Oscilloscope.
> 
> So, I connected the single oscilloscope probe to the output of a used
> function generator that I bought on EBay.
> 
> On oscilloscope auto, what I see is a waveform that I can only
> describe as a repeating sinc function. When I increase the frequency
> of the sine wave on the generator, I see more and more tiny waves
> appear in this sinc-like function. If I increase the amplitude on the
> generator I see these tiny waveforms in the sinc-like waves increase
> in amplitude.
> 
> This seems strange to me because I set the function generator for a
> repeating sine wave, but what I see is this repeating sinc-like
> waveform. The sinc waveform becomes more and more detailed.
> 
> Is the generator bad?
> 
Most function generators approximate a sinewave.  They are great
at generating triangle waves, and the square waves that are a byproduct,
but the sinewave is created by "smoothing" the triangle wave, usually
by a circuit of diodes and resistors.

Function generators are general purpose devices, and their sinewave 
out put is good enough for what they are intended for.

If you need a perfect sinewave, then you choose a generator that
starts with a sinewave, or at the very least uses frequency filtering
to get the sinewave.  But, those are usually cumbersome to switch
bands, and add a lot of overhead to the timing so rapidly sweeping
the generator is not in the picture.

If you are seeing the sinewave become smoother the higher the
frequency, likely you are seeing the frequency response of the scope
kick in.  Once you start hitting its limits, its frequency response
will affect the waveform.  Use a high enough frequency, or a scope
with a low enough response, and the scope loses much of its purpose,
since you can't tell whether that sinewave is really a sinewave, or
the frequency response of the scope is turning a signal into a sinewave.

  Michael

On Sun, 11 Nov 2007 15:06:39 -0800, Chris L <c...@aol.com>
wrote:

>Hello, I've been trying to learn how to use my new Protek 800 series
>hand held Digital Oscilloscope.
>
>So, I connected the single oscilloscope probe to the output of a used
>function generator that I bought on EBay.
>
>On oscilloscope auto, what I see is a waveform that I can only
>describe as a repeating sinc function. When I increase the frequency
>of the sine wave on the generator, I see more and more tiny waves
>appear in this sinc-like function. If I increase the amplitude on the
>generator I see these tiny waveforms in the sinc-like waves increase
>in amplitude.

What exactly do you mean by a "sinc function"?  My first thought was
that "sinc" was a typo for "sine", but it apparently isn't.

Can you describe the display more clearly, or better, put a picture of
it on a web site somewhere - then we'll have a better idea of what you
are seeing.


-- 
Peter Bennett, VE7CEI  
peterbb4 (at) interchange.ubc.ca  
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca

Peter Bennett wrote:

> On Sun, 11 Nov 2007 15:06:39 -0800, Chris L <c...@aol.com>
> wrote:
> 
> 
>>Hello, I've been trying to learn how to use my new Protek 800 series
>>hand held Digital Oscilloscope.
>>
>>So, I connected the single oscilloscope probe to the output of a used
>>function generator that I bought on EBay.
>>
>>On oscilloscope auto, what I see is a waveform that I can only
>>describe as a repeating sinc function. When I increase the frequency
>>of the sine wave on the generator, I see more and more tiny waves
>>appear in this sinc-like function. If I increase the amplitude on the
>>generator I see these tiny waveforms in the sinc-like waves increase
>>in amplitude.
> 
> 
> What exactly do you mean by a "sinc function"?  My first thought was
> that "sinc" was a typo for "sine", but it apparently isn't.
> 
> Can you describe the display more clearly, or better, put a picture of
> it on a web site somewhere - then we'll have a better idea of what you
> are seeing.
> 
> 
I think he has the unit set up incorrectly. It's generating 10% or duty 
cycle pulses for example.


-- 
"I'm never wrong, once i thought i was, but was mistaken"
Real Programmers Do things like this.
http://webpages.charter.net/jamie_5

"Peter Bennett" <p...@somewhere.invalid> wrote in message 
news:3...@news.supernews.com...
> On Sun, 11 Nov 2007 15:06:39 -0800, Chris L <c...@aol.com>
> wrote:
>
<snip>
>>On oscilloscope auto, what I see is a waveform that I can only
>>describe as a repeating sinc function. When I increase the frequency
>>of the sine wave on the generator, I see more and more tiny waves
>>appear in this sinc-like function. If I increase the amplitude on the
>>generator I see these tiny waveforms in the sinc-like waves increase
>>in amplitude.
>
> What exactly do you mean by a "sinc function"?  My first thought was
> that "sinc" was a typo for "sine", but it apparently isn't.
>
Peter,

For info on sinc function, see 
http://mathworld.wolfram.com/SincFunction.html

Chris L,
I'm not familiar with your particular o'scope (and I haven't time to look up 
the user's manual), but check to see if it has an FFT function and that it 
is turned off.

Good luck,
Richard

On Sun, 11 Nov 2007 15:06:39 -0800, Chris L <c...@aol.com>
wrote:

>Hello, I've been trying to learn how to use my new Protek 800 series
>hand held Digital Oscilloscope.
>
>So, I connected the single oscilloscope probe to the output of a used
>function generator that I bought on EBay.
>
>On oscilloscope auto, what I see is a waveform that I can only
>describe as a repeating sinc function. When I increase the frequency
>of the sine wave on the generator, I see more and more tiny waves
>appear in this sinc-like function. If I increase the amplitude on the
>generator I see these tiny waveforms in the sinc-like waves increase
>in amplitude.
>
>This seems strange to me because I set the function generator for a
>repeating sine wave, but what I see is this repeating sinc-like
>waveform. The sinc waveform becomes more and more detailed.
>
>Is the generator bad?
>
>How do I get a repeating sine wave without the sinc?

You can use the FREE signal generator that comes in my Daqarta
software package.  That will give you known-good waveforms to test,
and it also displays the waveforms (or spectra) with advanced
triggering options so you can compare with the hand-held.  The only
downside is that since it uses your computer's sound card, you will be
limited to audio-range signals (few Hz to 22 kHz, typically).

There is no need to purchase Daqarta for this.  The signal generator
and all the display functions (and most everything else except signal
inputs)  will continue to work after Daqarta's trial period expires.
You are welcome to use it this way as long as you like.

Best regards,


Bob Masta
 
              DAQARTA  v3.50
   Data AcQuisition And Real-Time Analysis
             www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
        Science with your sound card!

On Nov 11, 5:28 pm, Jamie
<jamie_ka1lpa_not_valid_after_ka1l...@charter.net> wrote:
> Peter Bennett wrote:
> > On Sun, 11 Nov 2007 15:06:39 -0800, Chris L <clusard...@aol.com>
> > wrote:
>
> >>Hello, I've been trying to learn how to use my new Protek 800 series
> >>hand held DigitalOscilloscope.
>
> >>So, I connected the singleoscilloscopeprobe to the output of a used
> >>function generator that I bought on EBay.
>
> >>Onoscilloscopeauto, what I see is a waveform that I can only
> >>describe as a repeating sinc function. When I increase the frequency
> >>of the sine wave on the generator, I see more and more tiny waves
> >>appear in this sinc-like function. If I increase the amplitude on the
> >>generator I see these tiny waveforms in the sinc-like waves increase
> >>in amplitude.
>
> > What exactly do you mean by a "sinc function"?  My first thought was
> > that "sinc" was a typo for "sine", but it apparently isn't.
>
> > Can you describe the display more clearly, or better, put a picture of
> > it on a web site somewhere - then we'll have a better idea of what you
> > are seeing.
>
> I think he has the unit set up incorrectly. It's generating 10% or duty
> cycle pulses for example.
>
> --
> "I'm never wrong, once i thought i was, but was mistaken"
> Real Programmers Do things like this.http://webpages.charter.net/jamie_5- Hide quoted text -
>
> - Show quoted text -

Hello, I went to Frys Electronics and bought a $350 function
generator, hooked it up, and got the exact same plot on the
oscilloscope.

What the plot looks like is this: consider a repeating sine wave. It
has 2 large side lobes which are smaller than the middle lobe. This
repeats the same way a sine wave repeats. If I then increase the
frequency on the function generator these repeating waves become more
developed/detailed.

It may be because the oscilloscope triggering is wrong!
       /\
      /  \
 /\  /    \  /\
/  \/      \/  \ ...


If increase frequency I get :
      ./\.
     ./  \.
./\. /    \../\.
/  \/      \/  \ ...
                                    /\
Consider the dots to be /   \. I.E.: Little sine waves

What should I do?

Chris Lusardi

On Fri, 16 Nov 2007 06:22:27 -0800 (PST), Chris L <c...@aol.com>
wrote:

>
>Hello, I went to Frys Electronics and bought a $350 function
>generator, hooked it up, and got the exact same plot on the
>oscilloscope.
>
>What the plot looks like is this: consider a repeating sine wave. It
>has 2 large side lobes which are smaller than the middle lobe. This
>repeats the same way a sine wave repeats. If I then increase the
>frequency on the function generator these repeating waves become more
>developed/detailed.
>
>It may be because the oscilloscope triggering is wrong!
>       /\
>      /  \
> /\  /    \  /\
>/  \/      \/  \ ...
>
>
>If increase frequency I get :
>      ./\.
>     ./  \.
>./\. /    \../\.
>/  \/      \/  \ ...
>                                    /\
>Consider the dots to be /   \. I.E.: Little sine waves
>
>What should I do?
>
>Chris Lusardi

What is the test frequency, and what is the sample rate of the scope?
What you describe sounds like what you see when the sample rate is
too slow for the test frequency.  Adjacent samples on the display
don't come from the same waveform cycle, but from subsequent cycles
whenever the A/D gets back to fetch them.  Since there is no sync
between the sample rate and the input signal, they don't form a single
complete waveform.  

You can try reducing the signal way down (say, a few 100 Hz) and see
if that gives a clean trace, then slowly bring up the frequency.

Digital scopes typically have a way to avoid this problem by sampling
only every Nth sample on the first trigger, then on the next trigger
they add a one-sample delay and again grab every Nth sample, etc.
So if N = 4, the first trigger will get samples 0, 4, 8, 12 ...   Then
the second trigger will get 1, 5, 9, 13..., the third will get 2, 6,
10, 14..., the fourth will get 3, 7, 11, 15... and the display will
put them all in the correct order.

I couldn't find any on-line info about the Protek 800, so I don't know
what its intrinsic sample rate is, or what they label the controls
that activate the above mechanism.  But I bet it's covered in the
manual.  <g>

Best regards,


Bob Masta
 
              DAQARTA  v3.50
   Data AcQuisition And Real-Time Analysis
             www.daqarta.com
Scope, Spectrum, Spectrogram, FREE Signal Generator
        Science with your sound card!

On Nov 17, 10:12 am, NoS...@daqarta.com (Bob Masta) wrote:
> On Fri, 16 Nov 2007 06:22:27 -0800 (PST), Chris L <clusard...@aol.com>
> wrote:
>
>
>
>
>
>
>
> >Hello, I went to Frys Electronics and bought a $350 function
> >generator, hooked it up, and got the exact same plot on the
> >oscilloscope.
>
> >What the plot looks like is this: consider a repeating sine wave. It
> >has 2 large side lobes which are smaller than the middle lobe. This
> >repeats the same way a sine wave repeats. If I then increase the
> >frequency on the function generator these repeating waves become more
> >developed/detailed.
>
> >It may be because theoscilloscopetriggering is wrong!
> >       /\
> >      /  \
> > /\  /    \  /\
> >/  \/      \/  \ ...
>
> >If increase frequency I get :
> >      ./\.
> >     ./  \.
> >./\. /    \../\.
> >/  \/      \/  \ ...
> >                                    /\
> >Consider the dots to be /   \. I.E.: Little sine waves
>
> >What should I do?
>
> >Chris Lusardi
>
> What is the test frequency, and what is the sample rate of the scope?
> What you describe sounds like what you see when the sample rate is
> too slow for the test frequency.  Adjacent samples on the display
> don't come from the same waveform cycle, but from subsequent cycles
> whenever the A/D gets back to fetch them.  Since there is no sync
> between the sample rate and the input signal, they don't form a single
> complete waveform.  
>
> You can try reducing the signal way down (say, a few 100 Hz) and see
> if that gives a clean trace, then slowly bring up the frequency.
>
> Digital scopes typically have a way to avoid this problem by sampling
> only every Nth sample on the first trigger, then on the next trigger
> they add a one-sample delay and again grab every Nth sample, etc.
> So if N = 4, the first trigger will get samples 0, 4, 8, 12 ...   Then
> the second trigger will get 1, 5, 9, 13..., the third will get 2, 6,
> 10, 14..., the fourth will get 3, 7, 11, 15... and the display will
> put them all in the correct order.
>
> I couldn't find any on-line info about the Protek 800, so I don't know
> what its intrinsic sample rate is, or what they label the controls
> that activate the above mechanism.  But I bet it's covered in the
> manual.  <g>
>
> Best regards,
>
> Bob Masta
>
>               DAQARTA  v3.50
>    Data AcQuisition And Real-Time Analysis
>              www.daqarta.com
> Scope, Spectrum, Spectrogram, FREE Signal Generator
>         Science with your sound card!- Hide quoted text -
>
> - Show quoted text -

Can the below information solve the problem?

Christopher Lusardi

The Operator's Manual says:
Product Standards and Specifications

Model               840
Bandwidth/
Sample Rate         400MHZ
                    Real Sampling 100MS/s per Channel, 200 MS/s Single
Channel                       with 2.5 GS/s Repetive Sampling

2 Input channels
input coupling: DC, AC, GND
input impedance IM +/- 1%, 20pF +/- 2pF
Probe attenuation x1 or x10
Max Input 300V direct input, 600V through 10:1 probe

Vertical
vertical resolution 8 bit
Volts/div range 5mV/div ~100V/div(1,2,5 step)
offset position +/- 5 div from center
vertical accuracy +/- 3%

Horizontal
Sec/Div Range 10ns/div ~ 50s/div
time base accuracy +/- 0.01%
Position Range pre-Trigger:20 div max. Post-Trigger: 1000div
Delay Resolution 1/250 of screen diameter
delay accuracy 0.04 divisins
delta time measurement accuracy +/- 3%
Modes Main, XY
XY Yes
Horizontal Pan and Zoom Yes

Trigger
Sources Channel A and B
Modes Normal, single, roll, auto trigger
Advanced selections edge, pulsewidth, pattern video
edge : trigger on a rising or falling edge of any source
pulsewidth: trigger on a positive or negative pulsewidth of any source
larger             than, less than, equal to or not equal the duration
width 200nS ~             10S
TV: NTSC, PAL, SECAM, Normal Video, Even field, Odd field, Line
#select
TV Sensitivity: 0.7 div trigger level
auto scale : yes
range: +/- 10 div from center of screen
Level Accuracy +/- 0.4 divisions
Level resolutions: 500 pixels
sensitivity: DC 5MHz - 0.5 div 1.5 divisions
noise rejections : yes
Coupling Modes: DC: DC Coupled trigger
                AC: AC Coupled trigger cutoff frequency < 1HZ
                HF-Refject: > 50KHz
                LF-Reject: > 30KHz
                Noise Reject: 3 times the DC coupled limits

Acquistion
Real-Time: 200MS/s single channel
Sample Rate : 100MS/s per channel
Waveform Interpolation : Dot, Linear, Sine, Pulse
Record Length: 125 Kbytes/channel
Acquisition Mode: Sample, Peak detect, envelope, average
peak detection: 10ns
Average: 2-256
Vertical resolution: 8 bit
same rate accuracy: 100ppm
Minimum sample rate: 100MS/s (250 ns to 50S/div)

Measurement
Automatic Measurement: Peak-to-peak, Maximum, amplitude, top,
base,                        positive/negative overshoot, preshoot,
RMS mean, one                             cycle mean, frequency
period, + width, - width, + - duty                         cycle, rise
time, fall time, delay, phase shift
Waveform math: Ch A + Ch B, Ch A - Ch B, Ch B - Ch A
Cursors : delta V voltage
Delta V : voltage diff between cursors
Delta T: Time difference between cursors
FFT : Model 840
Windows : Rectangular, Hamming, Hanning, Blackman-Harris
Amplitude Display: Variable dB (1/2/5/10 dB)
Maximum Frequency: 1.25 GHz

On Sat, 17 Nov 2007 15:51:49 -0800 (PST), Chris L <c...@aol.com>
wrote:


>Can the below information solve the problem?
>
>Christopher Lusardi
>
>The Operator's Manual says:
>Product Standards and Specifications
>
>Model               840
>Bandwidth/
>Sample Rate         400MHZ
>                    Real Sampling 100MS/s per Channel, 200 MS/s Single
>Channel                       with 2.5 GS/s Repetive Sampling
<further specs snipped...>

Not really - of more importance is the frequency and voltage of the
signal you are measuring, and the sweep rate, vertical gain and
trigger settings of the scope when you are doing these measurements.

A silly question: do you have the scope ground connected to the signal
generator?  You can get very strange displays if you only connect the
signal lead (tip of the test probe) without any ground connections.


-- 
Peter Bennett, VE7CEI  
peterbb4 (at) interchange.ubc.ca  
new newsgroup users info : http://vancouver-webpages.com/nnq
GPS and NMEA info: http://vancouver-webpages.com/peter
Vancouver Power Squadron: http://vancouver.powersquadron.ca