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Is there some black magic required to get higher order harmonics out
of an oscillator? I'm only trying to get 17.2Mhz out of a 3.44Mhz source and am thus far ....[snip].... John L. Reinartz, W1QP, published "A Fundamental-Reinforced Harmonic- Generating Circuit" in the July, 1937, issue of QST. I don't have a copy handy, but a followup article "Putting the Harmonic Generator to Work" in the April, 1938, QST contains this statement: "It will be remembered that in the harmonic-generator circuit the crystal oscillator was operated on the crystal frequency only, and that the following tube was used to generate the even and odd harmonics up to the 11th and 12th. For our present purpose, the 8th harmonic is sufficient; that is, 28 Mc. from an 80-meter crystal...." Hope this helps. --Myron. -- Five boxes preserve our freedoms: soap, ballot, witness, jury, and cartridge PhD EE (retired). "Barbershop" tenor. CDL(PTXS). W0PBV. (785) 539-4448 NRA Life Member and Certified Instructor (Home Firearm Safety, Rifle, Pistol) |
On Sun, 14 Mar 2004 14:30:28 +1000, Tony wrote:
Even worse than that - relying on simple reasoning (no maths), the 5th will be COMPLETELY suppressed when the input's rising and falling edges are spaced so they correspond in time with the SAME point in the 5th harmonic waveform, Nicely put. Something like Fourier analysis can be an equation that you can apply, or a reality you can visualize. When it becomes "simple reasoning" is when you truly understand it. I suppose that if a being were infinitely intelligent, it wouldn't need any math; everything would be obvious. John |
On Sun, 14 Mar 2004 14:30:28 +1000, Tony wrote:
Even worse than that - relying on simple reasoning (no maths), the 5th will be COMPLETELY suppressed when the input's rising and falling edges are spaced so they correspond in time with the SAME point in the 5th harmonic waveform, Nicely put. Something like Fourier analysis can be an equation that you can apply, or a reality you can visualize. When it becomes "simple reasoning" is when you truly understand it. I suppose that if a being were infinitely intelligent, it wouldn't need any math; everything would be obvious. John |
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On Sat, 13 Mar 2004 22:15:43 -0800, John Larkin
wrote: I suppose that if a being were infinitely intelligent, it wouldn't need any math; everything would be obvious. Yeah, but he wouldn't have much of a social life. -- The BBC: Licensed at public expense to spread lies. |
On Sat, 13 Mar 2004 22:15:43 -0800, John Larkin
wrote: I suppose that if a being were infinitely intelligent, it wouldn't need any math; everything would be obvious. Yeah, but he wouldn't have much of a social life. -- The BBC: Licensed at public expense to spread lies. |
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? -- The BBC: Licensed at public expense to spread lies. |
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? -- The BBC: Licensed at public expense to spread lies. |
Paul Burridge wrote in message . ..
Hi all, Is there some black magic required to get higher order harmonics out of an oscillator? I'm only trying to get 17.2Mhz out of a 3.44Mhz source and am thus far failing spectacularly. I've tried everything I can think of so far to no avail. C2's small size (3.3pF)is attenuating any 5th harmonic current by 6db into Q2's base biasing network, in both posted versions. 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? 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. RL |
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