LC_Tuning-Outside_the_Box

Is that tuning, or just successfully yanking around?

It's tuning, I did it in 0.05% steps for illustration, but you'd could put a pot in there and do continuous tuning, or, as I alluded, add a PFD and do effective PLL control.

(I think you meant "successively" rather than "successfully" :-) ...Jim Thompson

Duh! Make that 5% (0.05) steps :-( ...Jim Thompson

No, I mean successfully, as in "he used a 2x4 instead of a tack hammer, but he managed it". I'm not sure what you're contemplating using it for, but the further that you get from the actual LC resonance the more you'll be at the mercy of your active elements, with all of the noise and signal distortion problems that are inherent in such. I suppose that an LC- stabilized active filter is better than nothing, and may even have a place in a serious design, but it just screams "consumer grade" to me.

I was just showing that an LC can be electronically-tuned by adding an amplifier wrapped around a reactive element (with the feedback amount adjustable)... write the loop equations and you'll see.

At 100kHz I don't see any problems with active elements. At much higher frequencies, delay and phase effects _will_ complicate matters. ...Jim Thompson

I don't know if has any relevance but, i've been watching this thread and it occured to me that I've done similar by putting a loosely coupled turn on the coil and then load it accordingly.

Jamie

Has anyone tried testing Y5V with DC control and 60Vpp signal yet? Or is it still theoretical? Murata doesn't carry this value in 100-V rating.

Since Varicap range is usually in the first 30% of the voltage rating, there will be Q reducing factors with a large swing in Y5V. WHat is the ESR and loss Tan Delta?

I'm not arguing with the effect that you're achieving in the least. I'm just arguing about whether it merits the claim of tuning an LC. Tuning an LC-based active filter -- yes. Yanking around a poor unsuspecting LC in unnatural ways -- yes. Tuning an LC -- welllllll...

(Tube-type radios used a similar technique, where a variable-gain pentode was used as a feedback element, either as a phase modulator in FM transmission, or to make a tunable oscillator for AGC. It worked so well that when varactor diodes came along, everyone abandoned it.)

As I posted way upthread, see

Joerg has been strangely silent here, but previously he's let slip that he uses this sort of technique, which is why I gave him the credit in the first place.

Cheers

Phil Hobbs

Yanking? I think you're misunderstanding the whole concept. I'll write it up equation-style so you can see how it works. ...Jim Thompson

But doesn't it have to tune 20%, thus it has to see 20% of the swing, does it not? Or is the route part fixed padding and small part variable via Y5V? ...Jim Thompson

Either way works. Probably a method that would do the whole range and work reliably over temperature, component tolerance, and aging would require a few stages in series-parallel. You can apply +-+- bias to alternating sections. Pity about that -20%/+80% tolerance--it means that only a factor of 4 is actually usable.

Of course for a small-production device, maybe the part-to-part matching of devices on the same reel would allow a less cumbersome design. I've never used a Y5V in my life, AFAIR. I just think the idea of a 10:1 capacitance range up in the microfarads is cool.

Cheers

Phil Hobbs

Tried?

Don't have any Y5V so I grabbed a pair of Z5Us from the junk box, probably

I'll even add a selection of current manufacturers' products, at different temperatures and amplitudes, and do a write up, if you all wouldn't mind dropping in a few donations ;-)

Tim

-- Seven Transistor Labs Electrical Engineering Consultation Website:

I've previously modeled the Y5V curve, for simulation purposes...

One of these days I'll try it as a Varicap. ...Jim Thompson

Not consumer grade, putting a floating bipolar power amp in there, bashing the entire circulating current of the LC! A consumer grade product would have poorly paid assemblers hand-selecting caps from a huge bin of assorted values.

He should draw up the actual power amp, and its floating power supplies, and pick some heat sinks.

You missed the point... it doesn't need to be floating. A virtual ground is a ground.

And what's this noise about consumer grade? More bloviation ?>:-} ...Jim Thompson

Fun! How big was the amplitude.. Could you see the distortion?

Hmm are you looking for cash, or will you work for electronics? I could look through my junk piles and see what might be of interest :^)

Since hearing about it here, I've always wanted to try this trick... but don't really have a use for it.

George H.

I don't need any equations to see what's in your schematic. You've got a regular old LC resonator in there, whose behavior you are modifying with a voltage amplifier (E1) that effectively changes the capacitance. That's pretty simple.

But tossing E1 in there means that it's not really a resonant tank circuit any more -- it's an active filter with a coil, with all the drawbacks of an active filter, as well as the major drawback of an LC circuit.

Uhm... like equipment? Can always use power supplies I guess, something nice for the lab say. Or a spectrum analyzer, but I'm guessing that would be a bit much :) As for junk or parts, dunno... most of the stuff I need, I just order. Guess I wouldn't mind something interesting though.

Tim