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Selecting oscillator harmonic on multi-mode line for ultra-widebandVCO?
If I have a waveguide, coax, or even lumped varactor tuned LC tank,
could I simply select which harmonic I want it to oscillate at, by tunning a negative resistance? Perhaps with the use of a "register key", such as is on flutes and clarinets? I suppose that functions as a high-pass filter on the line, when the hole is unplugged. I'm interested in a multi-decade VCO, tuned with one control voltage and just a few switches. No, I don't want to heterodyne or synthesize, because I'm interested in the regenerative/super-regenerative capabilities. Any applicable app notes or articles? Dream on? -- Scott ********************************** DIY Piezo-Gyro, PCB Drill Bot & More Soon! http://home.comcast.net/~scottxs/ ********************************** |
Scott Stephens wrote in message news:tnamc.36397$0H1.3120575@attbi_s54...
If I have a waveguide, coax, or even lumped varactor tuned LC tank, could I simply select which harmonic I want it to oscillate at, by tunning a negative resistance? A coaxial resonator will resonate on (or near) odd harmonics of the lowest resonance, but you'll probably have trouble getting an LC tank to have significant response at harmonics. Then the tuning will be problematic, I think: you need to cover 3:1 for the lowest resonance, and only 5:3 for the second, 7:5 for the third, etc., but capacitive tuning would need a capacitance for the lowest resonance which is awkward for the higher ones. Maybe you could only use the resonator, say, at and above the 7th harmonic of the lowest resonance, and forget about the 1st, 3rd and 5th. Perhaps with the use of a "register key", such as is on flutes and clarinets? I suppose that functions as a high-pass filter on the line, when the hole is unplugged. Just as an overtone crystal oscillator selects the overtone, you should be able to do similarly with a coaxial resonator oscillator. There's likely a practical limit. (The coupling will change with which resonance is selected, no?) I'm interested in a multi-decade VCO, tuned with one control voltage and just a few switches. You can switch both the C and the L of an LC tank and cover a wide range...but it's often easier to just build separate oscillators and switch among them. No, I don't want to heterodyne or synthesize, because I'm interested in the regenerative/super-regenerative capabilities. Any applicable app notes or articles? Dream on? I predict there will be a whole lot to learn on your way to your goal...but remember the old regen radios that used plug-in coils for different bands? Some of them could cover quite a range. You may be able to accomplish something similar with diode switching. Cheers, Tom |
Scott Stephens wrote in message news:tnamc.36397$0H1.3120575@attbi_s54...
If I have a waveguide, coax, or even lumped varactor tuned LC tank, could I simply select which harmonic I want it to oscillate at, by tunning a negative resistance? A coaxial resonator will resonate on (or near) odd harmonics of the lowest resonance, but you'll probably have trouble getting an LC tank to have significant response at harmonics. Then the tuning will be problematic, I think: you need to cover 3:1 for the lowest resonance, and only 5:3 for the second, 7:5 for the third, etc., but capacitive tuning would need a capacitance for the lowest resonance which is awkward for the higher ones. Maybe you could only use the resonator, say, at and above the 7th harmonic of the lowest resonance, and forget about the 1st, 3rd and 5th. Perhaps with the use of a "register key", such as is on flutes and clarinets? I suppose that functions as a high-pass filter on the line, when the hole is unplugged. Just as an overtone crystal oscillator selects the overtone, you should be able to do similarly with a coaxial resonator oscillator. There's likely a practical limit. (The coupling will change with which resonance is selected, no?) I'm interested in a multi-decade VCO, tuned with one control voltage and just a few switches. You can switch both the C and the L of an LC tank and cover a wide range...but it's often easier to just build separate oscillators and switch among them. No, I don't want to heterodyne or synthesize, because I'm interested in the regenerative/super-regenerative capabilities. Any applicable app notes or articles? Dream on? I predict there will be a whole lot to learn on your way to your goal...but remember the old regen radios that used plug-in coils for different bands? Some of them could cover quite a range. You may be able to accomplish something similar with diode switching. Cheers, Tom |
I have built numerous VCO's that work as you describe.
A tuned coaxial line is used and the feedback is controlled by a capacitor. Making the capacitor small will allow harmonic oscillation, making it small will allow fundamental. Since you can make say a 9th overtone crystal oscillator, there is no reason why you can't make a 9th overtone transmission line resonator oscillator. Rick N6RK "Scott Stephens" wrote in message news:tnamc.36397$0H1.3120575@attbi_s54... If I have a waveguide, coax, or even lumped varactor tuned LC tank, could I simply select which harmonic I want it to oscillate at, by tunning a negative resistance? Perhaps with the use of a "register key", such as is on flutes and clarinets? I suppose that functions as a high-pass filter on the line, when the hole is unplugged. I'm interested in a multi-decade VCO, tuned with one control voltage and just a few switches. No, I don't want to heterodyne or synthesize, because I'm interested in the regenerative/super-regenerative capabilities. Any applicable app notes or articles? Dream on? -- Scott ********************************** DIY Piezo-Gyro, PCB Drill Bot & More Soon! http://home.comcast.net/~scottxs/ ********************************** |
I have built numerous VCO's that work as you describe.
A tuned coaxial line is used and the feedback is controlled by a capacitor. Making the capacitor small will allow harmonic oscillation, making it small will allow fundamental. Since you can make say a 9th overtone crystal oscillator, there is no reason why you can't make a 9th overtone transmission line resonator oscillator. Rick N6RK "Scott Stephens" wrote in message news:tnamc.36397$0H1.3120575@attbi_s54... If I have a waveguide, coax, or even lumped varactor tuned LC tank, could I simply select which harmonic I want it to oscillate at, by tunning a negative resistance? Perhaps with the use of a "register key", such as is on flutes and clarinets? I suppose that functions as a high-pass filter on the line, when the hole is unplugged. I'm interested in a multi-decade VCO, tuned with one control voltage and just a few switches. No, I don't want to heterodyne or synthesize, because I'm interested in the regenerative/super-regenerative capabilities. Any applicable app notes or articles? Dream on? -- Scott ********************************** DIY Piezo-Gyro, PCB Drill Bot & More Soon! http://home.comcast.net/~scottxs/ ********************************** |
Rick Karlquist N6RK wrote:
Finally a reply =) thanks, I have built numerous VCO's that work as you describe. No technical papers recommendations? A tuned coaxial line is used and the feedback is controlled by a capacitor. Making the capacitor small will allow harmonic oscillation, making it small will allow fundamental. That was an initial thought, that, given a flat-gain amp, like a MMIC, the coupling capacitors reactance would determine what frequency maximum power would be transfered. The reactance the amplifier I/O impedance matched the line I/O impedance. Since you can make say a 9th overtone crystal oscillator, there is no reason why you can't make a 9th overtone transmission line resonator oscillator. I'm thinking I should try a binary weighted series-L shunt-C ladder network, with varactors for the C. Could switch the varactors into forward conduction to tune out the end of the line, raising the frequency. Latest Microwave News describes a nonlinear ceramic (BaZrTiO) thin-film voltage-tuned capacitor. I've read about articles that use common ceramic caps as VCO's, even the capacitor-equivalent of magnetic amplifiers. The advantage of thin films is you can fabricate voltage-tuned filters, as well as individual caps. Now if I could just fabricate my own, using basement PCB lithographic techniques, or my microwave oven to plasma sputter the film. -- Scott ********************************** DIY Piezo-Gyro, PCB Drill Bot & More Soon! http://home.comcast.net/~scottxs/ ********************************** |
Rick Karlquist N6RK wrote:
Finally a reply =) thanks, I have built numerous VCO's that work as you describe. No technical papers recommendations? A tuned coaxial line is used and the feedback is controlled by a capacitor. Making the capacitor small will allow harmonic oscillation, making it small will allow fundamental. That was an initial thought, that, given a flat-gain amp, like a MMIC, the coupling capacitors reactance would determine what frequency maximum power would be transfered. The reactance the amplifier I/O impedance matched the line I/O impedance. Since you can make say a 9th overtone crystal oscillator, there is no reason why you can't make a 9th overtone transmission line resonator oscillator. I'm thinking I should try a binary weighted series-L shunt-C ladder network, with varactors for the C. Could switch the varactors into forward conduction to tune out the end of the line, raising the frequency. Latest Microwave News describes a nonlinear ceramic (BaZrTiO) thin-film voltage-tuned capacitor. I've read about articles that use common ceramic caps as VCO's, even the capacitor-equivalent of magnetic amplifiers. The advantage of thin films is you can fabricate voltage-tuned filters, as well as individual caps. Now if I could just fabricate my own, using basement PCB lithographic techniques, or my microwave oven to plasma sputter the film. -- Scott ********************************** DIY Piezo-Gyro, PCB Drill Bot & More Soon! http://home.comcast.net/~scottxs/ ********************************** |
"Scott Stephens" wrote in message news:hDWqc.26611$gr.2415597@attbi_s52... I'm thinking I should try a binary weighted series-L shunt-C ladder network, with varactors for the C. Could switch the varactors into forward conduction to tune out the end of the line, raising the frequency. I played with that idea on the simulator. Didn't seem to have a lot going for it. Latest Microwave News describes a nonlinear ceramic (BaZrTiO) thin-film voltage-tuned capacitor. I've read about articles that use common ceramic caps as VCO's, even the capacitor-equivalent of magnetic amplifiers. The advantage of thin films is you can fabricate voltage-tuned filters, as well as individual caps. I've been following those nonlinear ceramics (ie BST) for years. They don't seem very promising as a tuning diode replacement. The Q is too low, the tuning range is too restricted, and there are temperature problems. Rick N6RK |
"Scott Stephens" wrote in message news:hDWqc.26611$gr.2415597@attbi_s52... I'm thinking I should try a binary weighted series-L shunt-C ladder network, with varactors for the C. Could switch the varactors into forward conduction to tune out the end of the line, raising the frequency. I played with that idea on the simulator. Didn't seem to have a lot going for it. Latest Microwave News describes a nonlinear ceramic (BaZrTiO) thin-film voltage-tuned capacitor. I've read about articles that use common ceramic caps as VCO's, even the capacitor-equivalent of magnetic amplifiers. The advantage of thin films is you can fabricate voltage-tuned filters, as well as individual caps. I've been following those nonlinear ceramics (ie BST) for years. They don't seem very promising as a tuning diode replacement. The Q is too low, the tuning range is too restricted, and there are temperature problems. Rick N6RK |
Rick Karlquist N6RK wrote:
I'm thinking I should try a binary weighted series-L shunt-C ladder network, with varactors for the C. Could switch the varactors into forward conduction to tune out the end of the line, raising the frequency. I played with that idea on the simulator. Didn't seem to have a lot going for it. I just did an FFT on a step-pulse on a diode-switched, binary weighted LC ladder. Came out as I expected. Problem is the high-frequency resonances exist on when the low frequency sections are not shorted. Which will make transistor oscillator design interesting, if I don't use a 50 ohm MMIC. I've been following those nonlinear ceramics (ie BST) for years. They don't seem very promising as a tuning diode replacement. The Q is too low, the tuning range is too restricted, and there are temperature problems. The latest Microwave News article showed the Q as being better than varactor Q's, of under 10, IIRC. -- Scott KB9ETU ********************************** DIY Piezo-Gyro, PCB Drill Bot & More Soon! http://home.comcast.net/~scottxs/ ********************************** |
Rick Karlquist N6RK wrote:
I'm thinking I should try a binary weighted series-L shunt-C ladder network, with varactors for the C. Could switch the varactors into forward conduction to tune out the end of the line, raising the frequency. I played with that idea on the simulator. Didn't seem to have a lot going for it. I just did an FFT on a step-pulse on a diode-switched, binary weighted LC ladder. Came out as I expected. Problem is the high-frequency resonances exist on when the low frequency sections are not shorted. Which will make transistor oscillator design interesting, if I don't use a 50 ohm MMIC. I've been following those nonlinear ceramics (ie BST) for years. They don't seem very promising as a tuning diode replacement. The Q is too low, the tuning range is too restricted, and there are temperature problems. The latest Microwave News article showed the Q as being better than varactor Q's, of under 10, IIRC. -- Scott KB9ETU ********************************** DIY Piezo-Gyro, PCB Drill Bot & More Soon! http://home.comcast.net/~scottxs/ ********************************** |
ddwyer wrote:
A multimode delay line oscillator can be achieved by introducing a peaked gain response at the required overtone. How? A tuned filter? There's a hole in the bucket... (circular implementation) Alternatively with more than 360 degrees phase shift the oscillation which cannot change frequency instantaneously can be induced by continuously increasing phase and jumping from 360 to 0 degrees to sweep over multimodes. Wha? Could you expand on that? Thanks -- Scott ********************************** DIY Piezo-Gyro, PCB Drill Bot & More Soon! http://home.comcast.net/~scottxs/ ********************************** |
ddwyer wrote:
A multimode delay line oscillator can be achieved by introducing a peaked gain response at the required overtone. How? A tuned filter? There's a hole in the bucket... (circular implementation) Alternatively with more than 360 degrees phase shift the oscillation which cannot change frequency instantaneously can be induced by continuously increasing phase and jumping from 360 to 0 degrees to sweep over multimodes. Wha? Could you expand on that? Thanks -- Scott ********************************** DIY Piezo-Gyro, PCB Drill Bot & More Soon! http://home.comcast.net/~scottxs/ ********************************** |
In article vLWrc.13935$JC5.1310262@attbi_s54, Scott Stephens
writes ddwyer wrote: A multimode delay line oscillator can be achieved by introducing a peaked gain response at the required overtone. How? A tuned filter? There's a hole in the bucket... (circular implementation) Not quite. The delay line can be multioctave and the phase slope will be proportional the the delay. It may go through many 360 deg phase rotations over its bandwidth. An amplifier with much shallower phase slope can still have sufficient selectivity to determine which particular 360 deg rotation is oscillated. This has been done successfully with PAL bulk acoustic delay lines. The following is more contentious but I think it will work Alternatively with more than 360 degrees phase shift the oscillation which cannot change frequency instantaneously can be induced by continuously increasing phase and jumping from 360 to 0 degrees to sweep over multimodes. Wha? Could you expand on that? Not a lot. progressively changing phase with varicaps cannot carry on but the circuit does not know the difference between 360deg and 0 deg. Goniometers? used to do this for direction finding. Can also be done with mixers but that is more of a circular argument. Thanks -- ddwyer |
In article vLWrc.13935$JC5.1310262@attbi_s54, Scott Stephens
writes ddwyer wrote: A multimode delay line oscillator can be achieved by introducing a peaked gain response at the required overtone. How? A tuned filter? There's a hole in the bucket... (circular implementation) Not quite. The delay line can be multioctave and the phase slope will be proportional the the delay. It may go through many 360 deg phase rotations over its bandwidth. An amplifier with much shallower phase slope can still have sufficient selectivity to determine which particular 360 deg rotation is oscillated. This has been done successfully with PAL bulk acoustic delay lines. The following is more contentious but I think it will work Alternatively with more than 360 degrees phase shift the oscillation which cannot change frequency instantaneously can be induced by continuously increasing phase and jumping from 360 to 0 degrees to sweep over multimodes. Wha? Could you expand on that? Not a lot. progressively changing phase with varicaps cannot carry on but the circuit does not know the difference between 360deg and 0 deg. Goniometers? used to do this for direction finding. Can also be done with mixers but that is more of a circular argument. Thanks -- ddwyer |
ddwyer wrote:
In article vLWrc.13935$JC5.1310262@attbi_s54, Scott Stephens ddwyer wrote: A multimode delay line oscillator can be achieved by introducing a peaked gain response at the required overtone. The delay line can be multioctave and the phase slope will be proportional the the delay. It may go through many 360 deg phase rotations over its bandwidth. The phase slope is proportional to the delay. When I think of phase slope, I think of inductance or capacitance, reactance based phase shift. An amplifier with much shallower phase slope An amplifier with broad bandwidth, having the real, resistive impedance greater than the reactive impedance? can still have sufficient selectivity to determine which particular 360 deg rotation is oscillated. This has been done successfully with PAL bulk acoustic delay lines. I've played around with ring oscillators made from 3 (or more) transistors, 3 FETs and my favorite, 3 CMOS unbuffered inverter gates. I find I can tune these sine-wave ring oscillators between 8 and 20 : 1 range, by changing the bias gate voltage and source current. Perhaps more, after I try a few tricks. 20:1 isn't bad, but I don't see why I shouldn't be able to get 100,000:1 out of a transconductance-tuned phase shift oscillator. I guess you'd say these have a very shallow "phase slope". I was hoping to use them as a wide-band tuned circuit, by setting the gain just under the oscillation point. But I found they are very sensitive to harmonics. I can bet a delay line oscillator is going to have this same problem then? I've tried several ways to make a clean wide-range sine-wave oscillator and regenerative variable tuned circuit. -- Scott ********************************** DIY Piezo-Gyro, PCB Drill Bot & More Soon! http://home.comcast.net/~scottxs/ ********************************** |
ddwyer wrote:
In article vLWrc.13935$JC5.1310262@attbi_s54, Scott Stephens ddwyer wrote: A multimode delay line oscillator can be achieved by introducing a peaked gain response at the required overtone. The delay line can be multioctave and the phase slope will be proportional the the delay. It may go through many 360 deg phase rotations over its bandwidth. The phase slope is proportional to the delay. When I think of phase slope, I think of inductance or capacitance, reactance based phase shift. An amplifier with much shallower phase slope An amplifier with broad bandwidth, having the real, resistive impedance greater than the reactive impedance? can still have sufficient selectivity to determine which particular 360 deg rotation is oscillated. This has been done successfully with PAL bulk acoustic delay lines. I've played around with ring oscillators made from 3 (or more) transistors, 3 FETs and my favorite, 3 CMOS unbuffered inverter gates. I find I can tune these sine-wave ring oscillators between 8 and 20 : 1 range, by changing the bias gate voltage and source current. Perhaps more, after I try a few tricks. 20:1 isn't bad, but I don't see why I shouldn't be able to get 100,000:1 out of a transconductance-tuned phase shift oscillator. I guess you'd say these have a very shallow "phase slope". I was hoping to use them as a wide-band tuned circuit, by setting the gain just under the oscillation point. But I found they are very sensitive to harmonics. I can bet a delay line oscillator is going to have this same problem then? I've tried several ways to make a clean wide-range sine-wave oscillator and regenerative variable tuned circuit. -- Scott ********************************** DIY Piezo-Gyro, PCB Drill Bot & More Soon! http://home.comcast.net/~scottxs/ ********************************** |
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