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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 :-) -- The BBC: Licensed at public expense to spread lies. |
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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. -- The BBC: Licensed at public expense to spread lies. |
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