What kind of distortion is an asymmetrical sine wave?

[John - KD5YI]

Although I'm really not that young, I seem to be having a Junior Moment.

I had a circuit which produced a sine wave which had a peak positive
voltage of, say, 1V. The peak negative voltage was a tad greater, say
-1.1V. But, the average was zero over a full cycle. I have no way to
measure the distortion nor the spectrum.

Can someone give me a qualitative idea of what picture that wave might
produce on a SA and what its harmonic distribution might look like?

Accuracy not required. Just an idea so I can get a "feeling" for that
sort of thing.

Thanks,
John

 

[Phil Allison]

"John - KD5YI"

I had a circuit which produced a sine wave which had a peak positive
voltage of, say, 1V. The peak negative voltage was a tad greater,
say -1.1V. But, the average was zero over a full cycle. I have no way to
measure the distortion nor the spectrum.

Can someone give me a qualitative idea of what picture that wave might
produce on a SA and what its harmonic distribution might look like?

Accuracy not required. Just an idea so I can get a "feeling" for that sort
of thing.

** Really need to see the actual wave you are on about - can you take a pic
and post it somewhere.

If the positive half is kinda rounded off at the top while the negative side
is a sine shape - that is typical of second harmonic distortion in a
simple, one device amplifying stage with no NFB.

The spectrum contains mainly 2nd harmonic and some 4th.

If a sine wave looks rounded top and bottom ( or has a smooth kink near each
zero crossing ) - that is characteristic of 3rd harmonic and higher odd
harmonics.


...... Phil

 

[John - KD5YI]

"John - KD5YI"

** Really need to see the actual wave you are on about - can you take a pic
and post it somewhere.

If the positive half is kinda rounded off at the top while the negative side
is a sine shape - that is typical of second harmonic distortion in a
simple, one device amplifying stage with no NFB.

The spectrum contains mainly 2nd harmonic and some 4th.

If a sine wave looks rounded top and bottom ( or has a smooth kink near each
zero crossing ) - that is characteristic of 3rd harmonic and higher odd
harmonics.


..... Phil

Excellent!

Thanks Phil, that's the description I was looking for. Unfortunately,
the circuit is no longer functional, but that waveform and what it
represented (distortion-wise) was bothering me.

Cheers,
John

 

[m II]

"John - KD5YI" wrote in message

Although I'm really not that young, I seem to be having a Junior Moment.

I had a circuit which produced a sine wave which had a peak positive
voltage of, say, 1V. The peak negative voltage was a tad greater, say
-1.1V. But, the average was zero over a full cycle. I have no way to
measure the distortion nor the spectrum.

Can someone give me a qualitative idea of what picture that wave might
produce on a SA and what its harmonic distribution might look like?

Accuracy not required. Just an idea so I can get a "feeling" for that
sort of thing.

Thanks,
John

---------------
Measure about 16 amplitude points on the waveform from the same point on
adjacent cycles (one exact cycle) and then find some fast Fourier transform
software and plug in the values.

As posted by others a flat bottom waveform is indicative of some 2nd
harmonic but other harmonics are involved to keep the top of the waveform
looking rounded.

One fallacy that people will tell you is that Nth harmonics will make the
wave look like this and that. This only applies when the harmonic is in
phase with the fundamental at zero crossings. Third harmonics can flatten
the peak of a sine wave or increase the amplitude. This can be simulated in
Excel with it's charting abilities. We needed this to analyze some waveforms
on a job and a co-worker produced one with variable harmonics and variable
phase lag in about half an hour. It was really cool to play with the figures
and see what happens in different condition of noise.

mike

 

[John - KD5YI]

"John - KD5YI"

** Really need to see the actual wave you are on about - can you take a pic
and post it somewhere.

If the positive half is kinda rounded off at the top while the negative side
is a sine shape - that is typical of second harmonic distortion in a
simple, one device amplifying stage with no NFB.

The spectrum contains mainly 2nd harmonic and some 4th.

If a sine wave looks rounded top and bottom ( or has a smooth kink near each
zero crossing ) - that is characteristic of 3rd harmonic and higher odd
harmonics.


..... Phil

I meant to tell you.. You nailed the circuit! It was a single stage
amplifier where I was trying to get as much gain as possible so feedback
was minuscule.

Thanks again.

John

 

[John - KD5YI]

"John - KD5YI"

** Really need to see the actual wave you are on about - can you take a pic
and post it somewhere.

If the positive half is kinda rounded off at the top while the negative side
is a sine shape - that is typical of second harmonic distortion in a
simple, one device amplifying stage with no NFB.

The spectrum contains mainly 2nd harmonic and some 4th.

If a sine wave looks rounded top and bottom ( or has a smooth kink near each
zero crossing ) - that is characteristic of 3rd harmonic and higher odd
harmonics.


..... Phil

I meant to tell you.. You nailed the circuit! It was a single stage
amplifier where I was trying to get as much gain as possible so feedback
was minuscule.

Thanks again.

John

 

[John - KD5YI]

in message

Although I'm really not that young, I seem to be having a Junior Moment.

I had a circuit which produced a sine wave which had a peak positive
voltage of, say, 1V. The peak negative voltage was a tad greater, say
-1.1V. But, the average was zero over a full cycle. I have no way to
measure the distortion nor the spectrum.

Can someone give me a qualitative idea of what picture that wave might
produce on a SA and what its harmonic distribution might look like?

Accuracy not required. Just an idea so I can get a "feeling" for that
sort of thing.

Thanks,
John

---------------
Measure about 16 amplitude points on the waveform from the same point on
adjacent cycles (one exact cycle) and then find some fast Fourier
transform software and plug in the values.

As posted by others a flat bottom waveform is indicative of some 2nd
harmonic but other harmonics are involved to keep the top of the
waveform looking rounded.

Hey, mike -

Thanks for your reply. As I told Phil, the circuit is no longer
functional. Sorry I did not put that into my OP. But, it had been
bothering me for some time now. I think Phil nailed it.

One fallacy that people will tell you is that Nth harmonics will make
the wave look like this and that. This only applies when the harmonic is
in phase with the fundamental at zero crossings. Third harmonics can
flatten the peak of a sine wave or increase the amplitude. This can be
simulated in Excel with it's charting abilities. We needed this to
analyze some waveforms on a job and a co-worker produced one with
variable harmonics and variable phase lag in about half an hour. It was
really cool to play with the figures and see what happens in different
condition of noise.

mike

Sounds cool. I miss having someone to bounce ideas around with.

Cheers,
John

 

[John - KD5YI]

"John - KD5YI"

** Really need to see the actual wave you are on about - can you take a pic
and post it somewhere.

If the positive half is kinda rounded off at the top while the negative side
is a sine shape - that is typical of second harmonic distortion in a
simple, one device amplifying stage with no NFB.

The spectrum contains mainly 2nd harmonic and some 4th.

If a sine wave looks rounded top and bottom ( or has a smooth kink near each
zero crossing ) - that is characteristic of 3rd harmonic and higher odd
harmonics.


..... Phil

My apologies for the multiple post. Thunderbird went berserk on me and I
had to close and restart it.

Sorry.

John

 

[m II]

"John - KD5YI" wrote in message

in message

Although I'm really not that young, I seem to be having a Junior Moment.

I had a circuit which produced a sine wave which had a peak positive
voltage of, say, 1V. The peak negative voltage was a tad greater, say
-1.1V. But, the average was zero over a full cycle. I have no way to
measure the distortion nor the spectrum.

Can someone give me a qualitative idea of what picture that wave might
produce on a SA and what its harmonic distribution might look like?

Accuracy not required. Just an idea so I can get a "feeling" for that
sort of thing.

Thanks,
John

---------------
Measure about 16 amplitude points on the waveform from the same point on
adjacent cycles (one exact cycle) and then find some fast Fourier
transform software and plug in the values.

As posted by others a flat bottom waveform is indicative of some 2nd
harmonic but other harmonics are involved to keep the top of the
waveform looking rounded.

Hey, mike -

Thanks for your reply. As I told Phil, the circuit is no longer
functional. Sorry I did not put that into my OP. But, it had been
bothering me for some time now. I think Phil nailed it.

One fallacy that people will tell you is that Nth harmonics will make
the wave look like this and that. This only applies when the harmonic is
in phase with the fundamental at zero crossings. Third harmonics can
flatten the peak of a sine wave or increase the amplitude. This can be
simulated in Excel with it's charting abilities. We needed this to
analyze some waveforms on a job and a co-worker produced one with
variable harmonics and variable phase lag in about half an hour. It was
really cool to play with the figures and see what happens in different
condition of noise.

mike

Sounds cool. I miss having someone to bounce ideas around with.

Cheers,
John

-------------------


Soooo, you used to be a bouncer, then?


mike

 

[John - KD5YI]

in message



Hey, mike -

Thanks for your reply. As I told Phil, the circuit is no longer
functional. Sorry I did not put that into my OP. But, it had been
bothering me for some time now. I think Phil nailed it.



Sounds cool. I miss having someone to bounce ideas around with.

Cheers,
John

-------------------


Soooo, you used to be a bouncer, then?


mike

Haw! Well, not in the usual sense of the word.

John

 

[m II]

"John - KD5YI" wrote in message

"John - KD5YI"

** Really need to see the actual wave you are on about - can you take a
pic
and post it somewhere.

If the positive half is kinda rounded off at the top while the negative
side
is a sine shape - that is typical of second harmonic distortion in a
simple, one device amplifying stage with no NFB.

The spectrum contains mainly 2nd harmonic and some 4th.

If a sine wave looks rounded top and bottom ( or has a smooth kink near
each
zero crossing ) - that is characteristic of 3rd harmonic and higher odd
harmonics.


..... Phil

My apologies for the multiple post. Thunderbird went berserk on me and I
had to close and restart it.

Sorry.

John
-----------------

I always figured that is your NNTP not sending the "confirm" response. Your
news readers will continually try, again, until it gets that back to
indicate success.


mike

 

[John - KD5YI]

in message



My apologies for the multiple post. Thunderbird went berserk on me and I
had to close and restart it.

Sorry.

John
-----------------

I always figured that is your NNTP not sending the "confirm" response.
Your news readers will continually try, again, until it gets that back
to indicate success.


mike

Aha! Thanks for the explanation. It was probably as you say.

John

 

[Don Lancaster]

Excellent!

Thanks Phil, that's the description I was looking for. Unfortunately,
the circuit is no longer functional, but that waveform and what it
represented (distortion-wise) was bothering me.

Cheers,
John

Um, if you have half wave assymetry, that HAS to be caused by even
harmonics. The second is the most likely.

--
Many thanks,

Don Lancaster voice phone: (928)428-4073
Synergetics 3860 West First Street Box 809 Thatcher, AZ 85552
rss: http://www.tinaja.com/whtnu.xml email: [email protected]

Please visit my GURU's LAIR web site at http://www.tinaja.com

 

[Martin Brown]

I meant to tell you.. You nailed the circuit! It was a single stage
amplifier where I was trying to get as much gain as possible so feedback
was minuscule.

If the frequency is not too high then you could always download Daqarta
which will do basic scope functions and spectrum analysis on a PC using
the sound card for two input channels. ISTR it is good to about 50kHz.
It will easily show which harmonics are present in audio signals, but
the most likely cause is second harmonic if the waveform is assymetric
and smooth.

http://www.daqarta.com/

It will run for a month or so on evaluation and work as a signal
generator forever. It is nicely done with only the odd quirk. No
subsitute for a real scope in electronics but useful for public demos
when you want a projectable realtime spectrum analyser for voice or music.

Regards,
Martin Brown

 

[John - KD5YI]

If the frequency is not too high then you could always download Daqarta
which will do basic scope functions and spectrum analysis on a PC using
the sound card for two input channels. ISTR it is good to about 50kHz.
It will easily show which harmonics are present in audio signals, but
the most likely cause is second harmonic if the waveform is assymetric
and smooth.

http://www.daqarta.com/

It will run for a month or so on evaluation and work as a signal
generator forever. It is nicely done with only the odd quirk. No
subsitute for a real scope in electronics but useful for public demos
when you want a projectable realtime spectrum analyser for voice or music.

Regards,
Martin Brown

Thanks, Martin. Good idea.

Cheers,
John

 

[John - KD5YI]

1. Slightly flattened top (+ side).
2. "Peaky" bottom (- side).
3. Perfect sine with DC offset ruled out by criteria.

Gotcha. Thanks, Robert.

Cheers,
John