Selecting oscillator harmonic on multi-mode line for ultra-w

[Scott Stephens]

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

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[Rick Karlquist N6RK]

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" <scottxs@comcast.net> 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/

**********************************

 

[Scott Stephens]

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

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[Rick Karlquist N6RK]

"Scott Stephens" <scottxs@comcast.net> 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]

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

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[ddwyer]

In article <xufrc.87226$536.14704068@attbi_s03>, Scott Stephens
<scottxs@comcast.net> writes

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.
The musical instrument analogue replicates a delay line.

A delay line oscillator can be induced to oscillate over +-180 degrees
if the overall gain is >1. A multimode delay line oscillator can be
achieved by introducing a peaked gain response at the required overtone.
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.
..
--
ddwyer

 

[Scott Stephens]

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

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[ddwyer]

In article <vLWrc.13935$JC5.1310262@attbi_s54>, Scott Stephens
<scottxs@comcast.net> 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

 

[Scott Stephens]

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

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