On Wed, 17 Mar 2004 11:06:42 +1000, Tony wrote:

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"?

"Words mean what I choose them to mean! No more; no less."
- the Red Queen
:-)
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On 16 Mar 2004 16:54:06 -0800, (Tom Bruhns) wrote:

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.

What leads you to believe I have enough 5th harmonic in *my*
particular case? Are you satisfied with the square wave I posted? Does
it look up to the job?

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.

Currently 74HC but I've got some ACs (shouldn't need anything special
for this relatively low frequency target, I'd have thought).

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.

Should do, shouldn't it.

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.

I'm going to have a bash at this this afternoon. Not strictly
according to your suggestions at this stage, but I just want to know
if there's a sniff of 5th about at all.

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.

Still waiting to see evidence of that "abundance" - no sign so far.
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On 16 Mar 2004 16:54:06 -0800, (Tom Bruhns) wrote:

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.

What leads you to believe I have enough 5th harmonic in *my*
particular case? Are you satisfied with the square wave I posted? Does
it look up to the job?

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.

Currently 74HC but I've got some ACs (shouldn't need anything special
for this relatively low frequency target, I'd have thought).

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.

Should do, shouldn't it.

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.

I'm going to have a bash at this this afternoon. Not strictly
according to your suggestions at this stage, but I just want to know
if there's a sniff of 5th about at all.

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.

Still waiting to see evidence of that "abundance" - no sign so far.
--

The BBC: Licensed at public expense to spread lies.

On Tue, 16 Mar 2004 19:43:24 -0800, John Larkin
wrote:

On Tue, 16 Mar 2004 19:54:27 -0600, John Fields
wrote:

Just for grins, take a little trip over to a.b.s.e. (same subject
heading)and take a look at what John Larkin's series resonant filter
feeding a parallel resonant filter strategy looks like as far as
allowing you to get a fifth harmonic from a fundamental square wave
goes.

Okay, well at least I can see this one! Not sure about the SA trace,
though. Came out clearly enough but I'm not sure what you were trying
to prove by it. As for the 'scope traces, there doesn't seem to be any
phase correlation between the two and you don't indicate at what point
the probe was inserted. The square wave r/f slopes look a bit tardy,
too. What was the active device you used to generate them?

That's just a standard bandpass. What you do is pick a normalized
lowpass filter that has the response shape you like, say a Tchebychev
(I know... various spellings) and scale it to the impedance Z' and
bandwidth W' you want. Then series resonate each L with a C, and
parallel resonate each C with an L, both at some desired center
frequency. Voila (pardon my French) a bandpass that's 2W' wide.

It's basically the same type as Reg's program designed for me. That
was built on Sunday, tested and found to be bang on the money and
later today I shall try to see if it can be used to 'extract' the
elusive 5th. I have to admit I'll be surprised if there's nothing
there at all, but we'll have to wait and see. Don't touch that dial!
:-)



--

The BBC: Licensed at public expense to spread lies.

On Tue, 16 Mar 2004 19:43:24 -0800, John Larkin
wrote:

On Tue, 16 Mar 2004 19:54:27 -0600, John Fields
wrote:

Just for grins, take a little trip over to a.b.s.e. (same subject
heading)and take a look at what John Larkin's series resonant filter
feeding a parallel resonant filter strategy looks like as far as
allowing you to get a fifth harmonic from a fundamental square wave
goes.

Okay, well at least I can see this one! Not sure about the SA trace,
though. Came out clearly enough but I'm not sure what you were trying
to prove by it. As for the 'scope traces, there doesn't seem to be any
phase correlation between the two and you don't indicate at what point
the probe was inserted. The square wave r/f slopes look a bit tardy,
too. What was the active device you used to generate them?

That's just a standard bandpass. What you do is pick a normalized
lowpass filter that has the response shape you like, say a Tchebychev
(I know... various spellings) and scale it to the impedance Z' and
bandwidth W' you want. Then series resonate each L with a C, and
parallel resonate each C with an L, both at some desired center
frequency. Voila (pardon my French) a bandpass that's 2W' wide.

It's basically the same type as Reg's program designed for me. That
was built on Sunday, tested and found to be bang on the money and
later today I shall try to see if it can be used to 'extract' the
elusive 5th. I have to admit I'll be surprised if there's nothing
there at all, but we'll have to wait and see. Don't touch that dial!
:-)



--

The BBC: Licensed at public expense to spread lies.

On Wed, 17 Mar 2004 12:03:04 +0000, Paul Burridge
wrote:


Okay, well at least I can see this one! Not sure about the SA trace,
though. Came out clearly enough but I'm not sure what you were trying
to prove by it.

---
It's an FFT of what's coming out of Larkin's suggested two-stage
bandpass filter.

The first vertical marker (f1) goes through the first peak, 17.19MHz,
which proves the fifth is in a 3.44MHz square wave. The second marker
goes through 34.38, so so's the tenth.
---

As for the 'scope traces, there doesn't seem to be any
phase correlation between the two and you don't indicate at what point
the probe was inserted.

---
Are you kidding? Count the high frequency cycles between the first
leading edge and the same point on the second leading edge of the square
wave and you'll find there are exactly five.
---

The square wave r/f slopes look a bit tardy,
too.

---
That's because the generator wasn't isolated from the filter and you're
seeing the filter's input dragging it around.
---

What was the active device you used to generate them?

---
Tektronics FG502. Here's the layout:



[TEK FG502]-+-[BPF]-+-[TEK 2465A]---[HP5328A]
| |
| +-[HP54602B]
|
[TEK DC504]



--
John Fields

On Wed, 17 Mar 2004 12:03:04 +0000, Paul Burridge
wrote:


Okay, well at least I can see this one! Not sure about the SA trace,
though. Came out clearly enough but I'm not sure what you were trying
to prove by it.

---
It's an FFT of what's coming out of Larkin's suggested two-stage
bandpass filter.

The first vertical marker (f1) goes through the first peak, 17.19MHz,
which proves the fifth is in a 3.44MHz square wave. The second marker
goes through 34.38, so so's the tenth.
---

As for the 'scope traces, there doesn't seem to be any
phase correlation between the two and you don't indicate at what point
the probe was inserted.

---
Are you kidding? Count the high frequency cycles between the first
leading edge and the same point on the second leading edge of the square
wave and you'll find there are exactly five.
---

The square wave r/f slopes look a bit tardy,
too.

---
That's because the generator wasn't isolated from the filter and you're
seeing the filter's input dragging it around.
---

What was the active device you used to generate them?

---
Tektronics FG502. Here's the layout:



[TEK FG502]-+-[BPF]-+-[TEK 2465A]---[HP5328A]
| |
| +-[HP54602B]
|
[TEK DC504]



--
John Fields

On Wed, 17 Mar 2004 08:58:18 -0600, John Fields
wrote:



[TEK FG502]-+-[BPF]-+-[TEK 2465A]---[HP5328A]
| |
| +-[HP54602B]
|
[TEK DC504]


Should be:

+---------|IN1 |
| |TEK2465A|
[TEK FG502]-+-[BPF]-+-|IN2 OUT2|---[HP5328A]
| |
| +-[HP54602B]
|
[TEK DC504]


--
John Fields

On Wed, 17 Mar 2004 08:58:18 -0600, John Fields
wrote:



[TEK FG502]-+-[BPF]-+-[TEK 2465A]---[HP5328A]
| |
| +-[HP54602B]
|
[TEK DC504]


Should be:

+---------|IN1 |
| |TEK2465A|
[TEK FG502]-+-[BPF]-+-|IN2 OUT2|---[HP5328A]
| |
| +-[HP54602B]
|
[TEK DC504]


--
John Fields

On Wed, 17 Mar 2004 08:58:18 -0600, John Fields
wrote:

It's an FFT of what's coming out of Larkin's suggested two-stage
bandpass filter.

The first vertical marker (f1) goes through the first peak, 17.19MHz,
which proves the fifth is in a 3.44MHz square wave. The second marker
goes through 34.38, so so's the tenth.

Curious that there should be a sizeable pass response at the tenth
harmonic, isn't it? It doesn't appear to be *that* much down on the
intended pass frequency although there appears to be no indexing for
the y axis.

Are you kidding? Count the high frequency cycles between the first
leading edge and the same point on the second leading edge of the square
wave and you'll find there are exactly five.

Well, I admit I'm a bit of a greenhorn on these things, but to my eyes
there appears to be some phase difference. I'll accept your word for
it there isn't.

What was the active device you used to generate them?

---
Tektronics FG502. Here's the layout:



[TEK FG502]-+-[BPF]-+-[TEK 2465A]---[HP5328A]
| |
| +-[HP54602B]
|
[TEK DC504]

Many thanks. I hope it didn't involve you in too much setting-up time
to investigate this and post your findings.

--

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