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. Pity, as it does seem to Spice very well. A
5/6V TTL level square wave winds up as around .5 of a volt of 5th
harmonic, post-filtering. Not bad!
--

The BBC: Licensed at public expense to spread lies.

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).

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. :-)

By the way, when you post a waveform where traces are only identified
by node numbers, when the schematic provided is an image only, there's
no way we can know where the traces originate, unless you tell us.

My apologies. I'll try not to let it happen again.
--

The BBC: Licensed at public expense to spread lies.

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).

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. :-)

By the way, when you post a waveform where traces are only identified
by node numbers, when the schematic provided is an image only, there's
no way we can know where the traces originate, unless you tell us.

My apologies. I'll try not to let it happen again.
--

The BBC: Licensed at public expense to spread lies.

On Sun, 14 Mar 2004 15:55:04 -0500, Active8
wrote:

On Sun, 14 Mar 2004 13:14:40 +0000, Paul Burridge wrote:

On Sat, 13 Mar 2004 20:23:45 -0500, Active8
wrote:

Just a rough guess, since your calling on supreme beings...

The post is still vacant as yet...
:-)

That input cap... I take it the input source is a reasonable
estimate of your square wave... if the time constant of that input
RC net isn't right, it'll be a differentiator, and turn your square
wave into pulses coincident with the rising and falling edges. Your
scope trace suggested otherwise, but IIRC, at that tin=me you were
using the filter at the input to the mult., xo things have changed.

There's been no filtering (other than the selective properties of the
tank circuits) whatsoever employed thus far.

It doesn't look like you're biased in Class C. All the mults I've
seen are Class C biased with the tuned circuit on the collector. And
remember, when you're doing this later for some other purpose, in
Class C, the transistors Vceo - reverse breakdown - must be at least
twice the supply voltage.

Yup, perfectly correct. I must admit that going the class C route with
the tank tuned to the required harmonic was the way I was 'brought up'
as it were. Class C typically generates lots of harmonics as you
obviously know. This multiplier seems to be operating in class A,
which I admit is odd given its high linearity. But I didn't design the
multiplying stage you see here, but the guy who did is an RF expert so
I don't argue. :-)

But you've just given me an idea: maybe I should increase the value of
the 82 ohm base-ground resistor to increase drive signal level and tip
the stage into class C. Worth a try?

Nah. With a *sine* input, you'd bias it so it only conducts for less
than 180 degrees of the fundamental's cycle - keep the trans *out*
of conduction for the most part. Now that I think of it, yer using a
square wave and should have the stinkin' harmonic already, duh. What
was I thinkin'? I still wonder what that input cap is doing to the
edges. The trace you posted indicates it *might* be ok if nothing
changed.

Just for grins, get rid of that input cap and do whatever with the
bias to allow you to DC couple the multiplier. That's pretty class
C'ish assuming a 0 - 5V square wave. Don't fry your b-e junction.
Something's wiping out your 5th, so lets get that input RC outta
there.

Hi Mike,
I'm made your suggested changes and re-run the sim.
The new output result across the 1k resistor is now viewable on
abse....

--

The BBC: Licensed at public expense to spread lies.

On Sun, 14 Mar 2004 15:55:04 -0500, Active8
wrote:

On Sun, 14 Mar 2004 13:14:40 +0000, Paul Burridge wrote:

On Sat, 13 Mar 2004 20:23:45 -0500, Active8
wrote:

Just a rough guess, since your calling on supreme beings...

The post is still vacant as yet...
:-)

That input cap... I take it the input source is a reasonable
estimate of your square wave... if the time constant of that input
RC net isn't right, it'll be a differentiator, and turn your square
wave into pulses coincident with the rising and falling edges. Your
scope trace suggested otherwise, but IIRC, at that tin=me you were
using the filter at the input to the mult., xo things have changed.

There's been no filtering (other than the selective properties of the
tank circuits) whatsoever employed thus far.

It doesn't look like you're biased in Class C. All the mults I've
seen are Class C biased with the tuned circuit on the collector. And
remember, when you're doing this later for some other purpose, in
Class C, the transistors Vceo - reverse breakdown - must be at least
twice the supply voltage.

Yup, perfectly correct. I must admit that going the class C route with
the tank tuned to the required harmonic was the way I was 'brought up'
as it were. Class C typically generates lots of harmonics as you
obviously know. This multiplier seems to be operating in class A,
which I admit is odd given its high linearity. But I didn't design the
multiplying stage you see here, but the guy who did is an RF expert so
I don't argue. :-)

But you've just given me an idea: maybe I should increase the value of
the 82 ohm base-ground resistor to increase drive signal level and tip
the stage into class C. Worth a try?

Nah. With a *sine* input, you'd bias it so it only conducts for less
than 180 degrees of the fundamental's cycle - keep the trans *out*
of conduction for the most part. Now that I think of it, yer using a
square wave and should have the stinkin' harmonic already, duh. What
was I thinkin'? I still wonder what that input cap is doing to the
edges. The trace you posted indicates it *might* be ok if nothing
changed.

Just for grins, get rid of that input cap and do whatever with the
bias to allow you to DC couple the multiplier. That's pretty class
C'ish assuming a 0 - 5V square wave. Don't fry your b-e junction.
Something's wiping out your 5th, so lets get that input RC outta
there.

Hi Mike,
I'm made your suggested changes and re-run the sim.
The new output result across the 1k resistor is now viewable on
abse....

--

The BBC: Licensed at public expense to spread lies.

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

On Sun, 14 Mar 2004 19:51:50 GMT, James Meyer
wrote:

The other idea is to make a doubler and a trippler fed from the
fundamental and then feed them into a mixer to get the fifth. If the doubler
and trippler are active (class C) stages, you should get as many db out at the
higher frequency as you put in at the fundamental. The mixer can have gain too.
Three transistors, three tuned circuits, and Bob's yer uncle.

Jim


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


John

Because a square wave has to have a particular on to off ratio to get
enough fifth. Because a square wave needs those nasty logic gates. Because
three transistors are simpler.

Jim

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

On Sun, 14 Mar 2004 19:51:50 GMT, James Meyer
wrote:

The other idea is to make a doubler and a trippler fed from the
fundamental and then feed them into a mixer to get the fifth. If the doubler
and trippler are active (class C) stages, you should get as many db out at the
higher frequency as you put in at the fundamental. The mixer can have gain too.
Three transistors, three tuned circuits, and Bob's yer uncle.

Jim


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


John

Because a square wave has to have a particular on to off ratio to get
enough fifth. Because a square wave needs those nasty logic gates. Because
three transistors are simpler.

Jim

On Sun, 14 Mar 2004 21:27:19 +0000, Paul Burridge
posted this:

On Sun, 14 Mar 2004 19:51:50 GMT, James Meyer
wrote:

I'm still working on an LTspice version of a varactor multiplier using
the base-emitter junction of a class C amp as the varactor. Basically using an
"idler" tank or tanks to augment the fifth harmonic.

The other idea is to make a doubler and a trippler fed from the
fundamental and then feed them into a mixer to get the fifth. If the doubler
and trippler are active (class C) stages, you should get as many db out at the
higher frequency as you put in at the fundamental. The mixer can have gain too.
Three transistors, three tuned circuits, and Bob's yer uncle.

Jim, please remember the fundamental has to be in the order of
~3.5Mhz.

3.5 MHz... 3.5 GHz 3.5 uHz... makes no difference. The laws of physics
scale nicely for most electronic circuits. Although some ICs are getting
features small enough that the electrons have to line up single file. 8-)

Jim

On Sun, 14 Mar 2004 21:27:19 +0000, Paul Burridge
posted this:

On Sun, 14 Mar 2004 19:51:50 GMT, James Meyer
wrote:

I'm still working on an LTspice version of a varactor multiplier using
the base-emitter junction of a class C amp as the varactor. Basically using an
"idler" tank or tanks to augment the fifth harmonic.

The other idea is to make a doubler and a trippler fed from the
fundamental and then feed them into a mixer to get the fifth. If the doubler
and trippler are active (class C) stages, you should get as many db out at the
higher frequency as you put in at the fundamental. The mixer can have gain too.
Three transistors, three tuned circuits, and Bob's yer uncle.

Jim, please remember the fundamental has to be in the order of
~3.5Mhz.

3.5 MHz... 3.5 GHz 3.5 uHz... makes no difference. The laws of physics
scale nicely for most electronic circuits. Although some ICs are getting
features small enough that the electrons have to line up single file. 8-)

Jim

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

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

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

On Mon, 15 Mar 2004 20:03:24 +0000, John Woodgate
wrote:


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.

Either that, or a mistuned filter.

John

On Mon, 15 Mar 2004 20:03:24 +0000, John Woodgate
wrote:


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.

Either that, or a mistuned filter.

John

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

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

Eh?? Where did you get that from? I haven't even tried filtering yet!
I still haven't exhausted all the other suggestions made during the
course of this thread.

I think we have to supplement 'Read The Fascinating Manual' with 'RTCT'
- 'Read The Copulating Thread'.

Perhaps you should...
--

The BBC: Licensed at public expense to spread lies.

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

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

Eh?? Where did you get that from? I haven't even tried filtering yet!
I still haven't exhausted all the other suggestions made during the
course of this thread.

I think we have to supplement 'Read The Fascinating Manual' with 'RTCT'
- 'Read The Copulating Thread'.

Perhaps you should...
--

The BBC: Licensed at public expense to spread lies.

On Mon, 15 Mar 2004 20:03:24 +0000, John Woodgate
wrote:

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.

Not this particular problem, it isn't!

--

The BBC: Licensed at public expense to spread lies.

On Mon, 15 Mar 2004 20:03:24 +0000, John Woodgate
wrote:

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.

Not this particular problem, it isn't!

--

The BBC: Licensed at public expense to spread lies.

On Mon, 15 Mar 2004 23:00:49 +0000, Paul Burridge
wrote:

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

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

Eh?? Where did you get that from? I haven't even tried filtering yet!
I still haven't exhausted all the other suggestions made during the
course of this thread.

---
What???

According to your schematic, the input to R1 is a 2.16MHz square wave
and L1VC1 is a parallel tuned tank, (filter) tuned to 10.8MHz. So is
L2VC2C7. If you're not trying to do any filtering, what are those tanks
doing in there?

--
John Fields

On Mon, 15 Mar 2004 23:00:49 +0000, Paul Burridge
wrote:

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

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

Eh?? Where did you get that from? I haven't even tried filtering yet!
I still haven't exhausted all the other suggestions made during the
course of this thread.

---
What???

According to your schematic, the input to R1 is a 2.16MHz square wave
and L1VC1 is a parallel tuned tank, (filter) tuned to 10.8MHz. So is
L2VC2C7. If you're not trying to do any filtering, what are those tanks
doing in there?

--
John Fields

On Mon, 15 Mar 2004 23:00:49 +0000, Paul Burridge
posted this:

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

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

Eh?? Where did you get that from? I haven't even tried filtering yet!
I still haven't exhausted all the other suggestions made during the
course of this thread.

I think we have to supplement 'Read The Fascinating Manual' with 'RTCT'
- 'Read The Copulating Thread'.

Perhaps you should...

Errr... I read the thread. And in your first message you say. "All I
can get apart from the fundamental is a strong third harmonic on 10.32Mhz,
regardless of what I tune for. I've tried passing the osc output through two
successive inverter gates to sharpen it up, but still nothing beyond the third
appears after tuned amplification for the fifth."

If I'm not mistaken, "tuned amplification" IS "filtering".

Jim

On Mon, 15 Mar 2004 23:00:49 +0000, Paul Burridge
posted this:

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

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

Eh?? Where did you get that from? I haven't even tried filtering yet!
I still haven't exhausted all the other suggestions made during the
course of this thread.

I think we have to supplement 'Read The Fascinating Manual' with 'RTCT'
- 'Read The Copulating Thread'.

Perhaps you should...

Errr... I read the thread. And in your first message you say. "All I
can get apart from the fundamental is a strong third harmonic on 10.32Mhz,
regardless of what I tune for. I've tried passing the osc output through two
successive inverter gates to sharpen it up, but still nothing beyond the third
appears after tuned amplification for the fifth."

If I'm not mistaken, "tuned amplification" IS "filtering".

Jim

On Mon, 15 Mar 2004 17:42:59 -0600, John Fields
wrote:

What???

Yup!!!

According to your schematic, the input to R1 is a 2.16MHz square wave
and L1VC1 is a parallel tuned tank, (filter) tuned to 10.8MHz. So is
L2VC2C7. If you're not trying to do any filtering, what are those tanks
doing in there?

The frequency of the square wave is actually 3.43Mhz (IIRC) the figure
you quote from the schematic is the *period.* Plus, the tanks are
actually shown tuned to 18.75Mhz (well the first one is, anyway, but
since they're variable caps they can be tweaked for the desired
frequency of 17.2Mhz. I've no idea how you've arrived at 10.8Mhz!
Yes, I realise tanks are a form of filter hence in prior postings I've
stated I'd not used any form of filtering *other than* the tanks.

--

The BBC: Licensed at public expense to spread lies.

On Mon, 15 Mar 2004 17:42:59 -0600, John Fields
wrote:

What???

Yup!!!

According to your schematic, the input to R1 is a 2.16MHz square wave
and L1VC1 is a parallel tuned tank, (filter) tuned to 10.8MHz. So is
L2VC2C7. If you're not trying to do any filtering, what are those tanks
doing in there?

The frequency of the square wave is actually 3.43Mhz (IIRC) the figure
you quote from the schematic is the *period.* Plus, the tanks are
actually shown tuned to 18.75Mhz (well the first one is, anyway, but
since they're variable caps they can be tweaked for the desired
frequency of 17.2Mhz. I've no idea how you've arrived at 10.8Mhz!
Yes, I realise tanks are a form of filter hence in prior postings I've
stated I'd not used any form of filtering *other than* the tanks.

--

The BBC: Licensed at public expense to spread lies.

On Tue, 16 Mar 2004 12:51:06 GMT, James Meyer
wrote:

Errr... I read the thread. And in your first message you say. "All I
can get apart from the fundamental is a strong third harmonic on 10.32Mhz,
regardless of what I tune for. I've tried passing the osc output through two
successive inverter gates to sharpen it up, but still nothing beyond the third
appears after tuned amplification for the fifth."

If I'm not mistaken, "tuned amplification" IS "filtering".

An argument over semantics, then. AFAIC it's not filtering as such.
It introduces a high degree of selectivity, certainly. But when
someone says "filtering" I assume they're taking about a pi-network or
something of that sort, between stages or at the end of a chain of
stages.
--

The BBC: Licensed at public expense to spread lies.

On Tue, 16 Mar 2004 12:51:06 GMT, James Meyer
wrote:

Errr... I read the thread. And in your first message you say. "All I
can get apart from the fundamental is a strong third harmonic on 10.32Mhz,
regardless of what I tune for. I've tried passing the osc output through two
successive inverter gates to sharpen it up, but still nothing beyond the third
appears after tuned amplification for the fifth."

If I'm not mistaken, "tuned amplification" IS "filtering".

An argument over semantics, then. AFAIC it's not filtering as such.
It introduces a high degree of selectivity, certainly. But when
someone says "filtering" I assume they're taking about a pi-network or
something of that sort, between stages or at the end of a chain of
stages.
--

The BBC: Licensed at public expense to spread lies.

Paul wrote,

On Tue, 16 Mar 2004 12:51:06 GMT, James Meyer
wrote:

Errr... I read the thread. And in your first message you say. "All I
can get apart from the fundamental is a strong third harmonic on 10.32Mhz,
regardless of what I tune for. I've tried passing the osc output through two
successive inverter gates to sharpen it up, but still nothing beyond the
third
appears after tuned amplification for the fifth."

If I'm not mistaken, "tuned amplification" IS "filtering".

An argument over semantics, then. AFAIC it's not filtering as such.
It introduces a high degree of selectivity, certainly. But when
someone says "filtering" I assume they're taking about a pi-network or
something of that sort, between stages or at the end of a chain of
stages.
--


You need to read up on active filters, and when you've done that, you should
read a book on digital filtering.
73,
Tom Donaly, KA6RUH

Paul wrote,

On Tue, 16 Mar 2004 12:51:06 GMT, James Meyer
wrote:

Errr... I read the thread. And in your first message you say. "All I
can get apart from the fundamental is a strong third harmonic on 10.32Mhz,
regardless of what I tune for. I've tried passing the osc output through two
successive inverter gates to sharpen it up, but still nothing beyond the
third
appears after tuned amplification for the fifth."

If I'm not mistaken, "tuned amplification" IS "filtering".

An argument over semantics, then. AFAIC it's not filtering as such.
It introduces a high degree of selectivity, certainly. But when
someone says "filtering" I assume they're taking about a pi-network or
something of that sort, between stages or at the end of a chain of
stages.
--


You need to read up on active filters, and when you've done that, you should
read a book on digital filtering.
73,
Tom Donaly, KA6RUH

FWIW, just now I had not trouble at all filtering the fifth out of a
square wave, in exactly the way I suggest below. It seems very silly
to me to put nonlinear elements in when you already have plenty of the
harmonic you want. I don't know what logic family you're using, but
if it's a modern one like 74AC, you should have several milliwatts of
fifth harmonic available. A simple series resonant LC from the logic
output to the base of a 2N2219-type transistor should get you at least
a couple mA RMS of fifth harmonic base current, assuming a
grounded-emitter stage with roughly 50 ohms input resistance. Make
the loaded Q of the LC something around 10 to 20, and you won't screw
up the amplifier with other harmonics or the fundamental. Be a bit
careful about the coil you use, because it will be fairly high
inductance for the frequency you're interested in...that is, keep the
unloaded Q and the self-resonant frequency high enough. Use another
moderate-Q tank in the collector circuit; you should be able to get
over 100mW of fifth, with other harmonics down 40dB or more. You can
get more complicated with the filtering if it's necessary, but for
fixed-frequency operation, there's nothing wrong with simple
synchronous tuning of single resonators set to reasonably high Q. If
you insist on using the unnecessary complication of a multi-pole
bandpass filter, be sure the one from the square wave to the amplifier
starts with a series resonator, not a shunt resonator.

Sheesh...all you need to do is selectively amplify the harmonic you
want; it's already there. Don't add complexity trying to generate
something you already have in abundance.


Paul Burridge wrote in message . ..
On Mon, 15 Mar 2004 20:03:24 +0000, John Woodgate
wrote:

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.

Not this particular problem, it isn't!

FWIW, just now I had not trouble at all filtering the fifth out of a
square wave, in exactly the way I suggest below. It seems very silly
to me to put nonlinear elements in when you already have plenty of the
harmonic you want. I don't know what logic family you're using, but
if it's a modern one like 74AC, you should have several milliwatts of
fifth harmonic available. A simple series resonant LC from the logic
output to the base of a 2N2219-type transistor should get you at least
a couple mA RMS of fifth harmonic base current, assuming a
grounded-emitter stage with roughly 50 ohms input resistance. Make
the loaded Q of the LC something around 10 to 20, and you won't screw
up the amplifier with other harmonics or the fundamental. Be a bit
careful about the coil you use, because it will be fairly high
inductance for the frequency you're interested in...that is, keep the
unloaded Q and the self-resonant frequency high enough. Use another
moderate-Q tank in the collector circuit; you should be able to get
over 100mW of fifth, with other harmonics down 40dB or more. You can
get more complicated with the filtering if it's necessary, but for
fixed-frequency operation, there's nothing wrong with simple
synchronous tuning of single resonators set to reasonably high Q. If
you insist on using the unnecessary complication of a multi-pole
bandpass filter, be sure the one from the square wave to the amplifier
starts with a series resonator, not a shunt resonator.

Sheesh...all you need to do is selectively amplify the harmonic you
want; it's already there. Don't add complexity trying to generate
something you already have in abundance.


Paul Burridge wrote in message . ..
On Mon, 15 Mar 2004 20:03:24 +0000, John Woodgate
wrote:

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.

Not this particular problem, it isn't!

On Tue, 16 Mar 2004 20:26:15 +0000, Paul Burridge
wrote:
If I'm not mistaken, "tuned amplification" IS "filtering".

An argument over semantics, then. AFAIC it's not filtering as such.
It introduces a high degree of selectivity, certainly. But when
someone says "filtering" I assume they're taking about a pi-network or
something of that sort, between stages or at the end of a chain of
stages.

Wow - the strange things you learn on this thread! So how many poles does a
circuit need for it to be called a "filter"?

Tony (remove the "_" to reply by email)