Paul Burridge wrote in message . ..
On 14 Mar 2004 10:01:00 -0800, (R.Legg) wrote:

C2's small size (3.3pF)is attenuating any 5th harmonic current by 6db
into
Q2's base biasing network, in both posted versions.

Curious. Can you show some figures to back this claim up? (Not that I
don't believe you; just that I'd like to see how you arrived at this
view).

The reactance of the C2 part is almost 3K at the fifth harmonic.

Input impedance of the biasing network is 300 ohms - this is about
half the small signal input impedance of the 3904 @4mA.

Even with bypassed emitter, only 1/3 of C2's AC current will enter the
base of Q2.

If the resonant circuit used lower L and higher C values, C2 could be
increased without as severe an effect as it has here.


Biasing the first stage as classC in the second revision is a pretty
drastic change from the previous class A revision (100mW). Don't you
believe in tiny steps?

I've been trying nothing else *but* "tiny steps" for the last few
days. There's no harm in the ocassional quantum jump. :-)

As previous posters have stated, if the input is squarish then the
harmonics are already there.

There is a +/- 3% window on all the optimum duty cycles (ie 10, 30,
50, 70, 90%), including risetime, for which the 5th harmonic amplitude
is relatively constant, at about 10% of the initial peak amplitude.
Note that the 30/70% period is a median quasi-minima for both 3rd and
4th harmonics, possibly reducing LF filtering problems in the first
stage, as the 1st and 2nd are farther away. 50% being available, you
should stick to it.

I don't know if you're doing any actual physical breadboarding. The
100mW power dissipation suggests not. Pre-apps it's time.

If this is a physical breadboard, then perhaps you might let us know
what you are actually using for your 2uH inductors. You wouldn't want
the relatively hefty classA bias to have any effect on them, so there
should be a lot of air in their flux path - not a couple of turns on a
bead, I hope.

RL

On 14 Mar 2004 23:43:57 -0800, (R.Legg) wrote:

The reactance of the C2 part is almost 3K at the fifth harmonic.

Input impedance of the biasing network is 300 ohms - this is about
half the small signal input impedance of the 3904 @4mA.

Even with bypassed emitter, only 1/3 of C2's AC current will enter the
base of Q2.

Understood. I chose a very low value for C2 because it was the third
harmonic that was dominating and most needed cutting down to size.
Though the reactance at the fifth is high, it's a lot higher still at
the third. Although I suppose I could have used a simple series L/C
tuned circuit tuned to pass on the fifth and attenuate everything
else. Do you think that might work?

If the resonant circuit used lower L and higher C values, C2 could be
increased without as severe an effect as it has here.

Good point.

As previous posters have stated, if the input is squarish then the
harmonics are already there.

Theoretically, perhaps! Damned if I can find the 5th, though. :(

There is a +/- 3% window on all the optimum duty cycles (ie 10, 30,
50, 70, 90%), including risetime, for which the 5th harmonic amplitude
is relatively constant, at about 10% of the initial peak amplitude.
Note that the 30/70% period is a median quasi-minima for both 3rd and
4th harmonics, possibly reducing LF filtering problems in the first
stage, as the 1st and 2nd are farther away. 50% being available, you
should stick to it.

I'm as close to 50% as I can get. If square waves are so finicky about
producing the 5th if their mark/space ratios are a tiny bit out then
maybe I need to consider some other way of generating such harmonics.

I don't know if you're doing any actual physical breadboarding. The
100mW power dissipation suggests not. Pre-apps it's time.

I'm using my 'leopardboard' technique: a layer of PCB with liittle
island pads etched out in copper and component ends soldered to those
islands.

If this is a physical breadboard, then perhaps you might let us know
what you are actually using for your 2uH inductors. You wouldn't want
the relatively hefty classA bias to have any effect on them, so there
should be a lot of air in their flux path - not a couple of turns on a
bead, I hope.

Nope. They should be okay. 5mm dia, air-core, 20mm winding length
--

The BBC: Licensed at public expense to spread lies.

On 14 Mar 2004 23:43:57 -0800, (R.Legg) wrote:

The reactance of the C2 part is almost 3K at the fifth harmonic.

Input impedance of the biasing network is 300 ohms - this is about
half the small signal input impedance of the 3904 @4mA.

Even with bypassed emitter, only 1/3 of C2's AC current will enter the
base of Q2.

Understood. I chose a very low value for C2 because it was the third
harmonic that was dominating and most needed cutting down to size.
Though the reactance at the fifth is high, it's a lot higher still at
the third. Although I suppose I could have used a simple series L/C
tuned circuit tuned to pass on the fifth and attenuate everything
else. Do you think that might work?

If the resonant circuit used lower L and higher C values, C2 could be
increased without as severe an effect as it has here.

Good point.

As previous posters have stated, if the input is squarish then the
harmonics are already there.

Theoretically, perhaps! Damned if I can find the 5th, though. :(

There is a +/- 3% window on all the optimum duty cycles (ie 10, 30,
50, 70, 90%), including risetime, for which the 5th harmonic amplitude
is relatively constant, at about 10% of the initial peak amplitude.
Note that the 30/70% period is a median quasi-minima for both 3rd and
4th harmonics, possibly reducing LF filtering problems in the first
stage, as the 1st and 2nd are farther away. 50% being available, you
should stick to it.

I'm as close to 50% as I can get. If square waves are so finicky about
producing the 5th if their mark/space ratios are a tiny bit out then
maybe I need to consider some other way of generating such harmonics.

I don't know if you're doing any actual physical breadboarding. The
100mW power dissipation suggests not. Pre-apps it's time.

I'm using my 'leopardboard' technique: a layer of PCB with liittle
island pads etched out in copper and component ends soldered to those
islands.

If this is a physical breadboard, then perhaps you might let us know
what you are actually using for your 2uH inductors. You wouldn't want
the relatively hefty classA bias to have any effect on them, so there
should be a lot of air in their flux path - not a couple of turns on a
bead, I hope.

Nope. They should be okay. 5mm dia, air-core, 20mm winding length
--

The BBC: Licensed at public expense to spread lies.

On Sun, 14 Mar 2004 21:27:21 +0000, Paul Burridge
wrote:

On Sun, 14 Mar 2004 12:04:18 -0800, John Larkin
wrote:


Why not just bandpass filter the 5th from the square wave? Too simple?

I suggested this a while ago, but no one seemed very keen on that
solution for some reason.

Write down their names for me please, so I can remember to not hire
them.

John

On Sun, 14 Mar 2004 21:27:21 +0000, Paul Burridge
wrote:

On Sun, 14 Mar 2004 12:04:18 -0800, John Larkin
wrote:


Why not just bandpass filter the 5th from the square wave? Too simple?

I suggested this a while ago, but no one seemed very keen on that
solution for some reason.

Write down their names for me please, so I can remember to not hire
them.

John

I read in sci.electronics.design that John Larkin jjlarkin@highSNIPland
THIStechPLEASEnology.com wrote (in qvrb50hvn0t1nj7kq5cako00bjrtis7nnr@
4ax.com) about 'Extracting the 5th Harmonic', on Mon, 15 Mar 2004:
On Sun, 14 Mar 2004 21:27:21 +0000, Paul Burridge
wrote:

On Sun, 14 Mar 2004 12:04:18 -0800, John Larkin
wrote:


Why not just bandpass filter the 5th from the square wave? Too simple?

I suggested this a while ago, but no one seemed very keen on that
solution for some reason.

Write down their names for me please, so I can remember to not hire
them.

The reason no-one seemed keen is that the OP's **complaint** was that
his 5th harmonic BP filter didn't produce any output.

I think we have to supplement 'Read The Fascinating Manual' with 'RTCT'
- 'Read The Copulating Thread'.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

I read in sci.electronics.design that John Larkin jjlarkin@highSNIPland
THIStechPLEASEnology.com wrote (in qvrb50hvn0t1nj7kq5cako00bjrtis7nnr@
4ax.com) about 'Extracting the 5th Harmonic', on Mon, 15 Mar 2004:
On Sun, 14 Mar 2004 21:27:21 +0000, Paul Burridge
wrote:

On Sun, 14 Mar 2004 12:04:18 -0800, John Larkin
wrote:


Why not just bandpass filter the 5th from the square wave? Too simple?

I suggested this a while ago, but no one seemed very keen on that
solution for some reason.

Write down their names for me please, so I can remember to not hire
them.

The reason no-one seemed keen is that the OP's **complaint** was that
his 5th harmonic BP filter didn't produce any output.

I think we have to supplement 'Read The Fascinating Manual' with 'RTCT'
- 'Read The Copulating Thread'.
--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk

On Mon, 15 Mar 2004 19:05:02 +0000, John Woodgate
wrote:

I read in sci.electronics.design that John Larkin jjlarkin@highSNIPland
THIStechPLEASEnology.com wrote (in qvrb50hvn0t1nj7kq5cako00bjrtis7nnr@
4ax.com) about 'Extracting the 5th Harmonic', on Mon, 15 Mar 2004:
On Sun, 14 Mar 2004 21:27:21 +0000, Paul Burridge
wrote:

On Sun, 14 Mar 2004 12:04:18 -0800, John Larkin
m wrote:


Why not just bandpass filter the 5th from the square wave? Too simple?

I suggested this a while ago, but no one seemed very keen on that
solution for some reason.

Write down their names for me please, so I can remember to not hire
them.

The reason no-one seemed keen is that the OP's **complaint** was that
his 5th harmonic BP filter didn't produce any output.


So I guess Fourier was wrong; makes sense, with a French name like
that. Somebody in this group also proved Shannon to be wrong... does
anybody remember who?

John

On Mon, 15 Mar 2004 19:05:02 +0000, John Woodgate
wrote:

I read in sci.electronics.design that John Larkin jjlarkin@highSNIPland
THIStechPLEASEnology.com wrote (in qvrb50hvn0t1nj7kq5cako00bjrtis7nnr@
4ax.com) about 'Extracting the 5th Harmonic', on Mon, 15 Mar 2004:
On Sun, 14 Mar 2004 21:27:21 +0000, Paul Burridge
wrote:

On Sun, 14 Mar 2004 12:04:18 -0800, John Larkin
m wrote:


Why not just bandpass filter the 5th from the square wave? Too simple?

I suggested this a while ago, but no one seemed very keen on that
solution for some reason.

Write down their names for me please, so I can remember to not hire
them.

The reason no-one seemed keen is that the OP's **complaint** was that
his 5th harmonic BP filter didn't produce any output.


So I guess Fourier was wrong; makes sense, with a French name like
that. Somebody in this group also proved Shannon to be wrong... does
anybody remember who?

John

I read in sci.electronics.design that John Larkin jjlarkin@highSNIPland
THIStechPLEASEnology.com wrote (in lr1c50ls8v4stqisn34rcd8eoc4bkqu4vo@
4ax.com) about 'Extracting the 5th Harmonic', on Mon, 15 Mar 2004:
spam.yuk wrote:

I read in sci.electronics.design that John Larkin jjlarkin@highSNIPland
THIStechPLEASEnology.com wrote (in qvrb50hvn0t1nj7kq5cako00bjrtis7nnr@
4ax.com) about 'Extracting the 5th Harmonic', on Mon, 15 Mar 2004:
On Sun, 14 Mar 2004 21:27:21 +0000, Paul Burridge
wrote:

On Sun, 14 Mar 2004 12:04:18 -0800, John Larkin
wrote:


Why not just bandpass filter the 5th from the square wave? Too simple?

I suggested this a while ago, but no one seemed very keen on that
solution for some reason.

Write down their names for me please, so I can remember to not hire
them.

The reason no-one seemed keen is that the OP's **complaint** was that
his 5th harmonic BP filter didn't produce any output.


So I guess Fourier was wrong; makes sense, with a French name like that.

No, what has emerged from the discussion is that rather small deviations
from a perfect square waveform can drastically reduce the amount of one
or more harmonics in the spectrum, and this probably is the source of
the problem.

--
Regards, John Woodgate, OOO - Own Opinions Only.
The good news is that nothing is compulsory.
The bad news is that everything is prohibited.
http://www.jmwa.demon.co.uk Also see http://www.isce.org.uk