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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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