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)