Ultra low frequency VCO

I'm mainly here to talk about electronics. One-upmanship also tends to intimidate the newbies, which I really don't want to do. I try not to dispense Bad Info myself, and try to help other people's misunderstandings when I can. Otherwise I just read with interest and learn stuff.

Whit3rd seems to be talking about the phase correlations rather than the instantaneous phase noise. Both multivibrators and LC resonators obey equations with full locality, i.e. neither one has any memory at all.

For instance, if you have a 1 MHz resonator with a Q of a million, it takes a second or so to get its phase to change when you put PM on the drive waveform. OTOH, if you change the resonant frequency suddenly, e.g. by putting 100V on a Y5V tank capacitor, the resonant frequency changes immediately--much faster than 1/Q cycles.

Because of the switching action, multivibrators intermodulate the switching element's noise at all frequencies, which makes their jitter much worse; also the effective Q of a multivibrator is less than 1, which means that there isn't any significant filtering action from the resonator. (That's frequency-domain way of thinking about what Whit3rd is talking about in the time domain--the conservation of energy issue is easier to think about if there's a natural bandwidth limit to the sqrt(t) behaviour.) The physical origin of the phase modulation doesn't change the way it varies with division ratio, though.

Cheers

Phil Hobbs

The point is that a lot of this jiber-jaber is pointless. Without the OP giving a better definition of the problem it=92s a guess at best which measurement technique is required.

He never did state the basis for his phase noise number, nor did he have an offset frequency.

The challenge in making =96100 dBc or better measurements is a function of the offset frequency and bandwidth. Center frequency isn=92t the issue here.

You may not be interested, but perhaps other folks are. And how big an offset frequency can he have on a 60 Hz carrier, anyway?

Cheers

Phil Hobbs

There's no one-up-man-ship involved. Larkin won't (or can't, because he doesn't really understand it) show where the extra charge came from. You (or Win) could put a stop to Larkin's nonsense. Larkin displays me as a fool, and the newbies don't know any better, so they'll never ever learn the correct solution unless someone (politically :) respected steps in.

Yep. ...Jim Thompson

It=92s not that it=92s not interesting =85 but you need to change the topic to phase noise measurements or something of that nature. Or stable low freq Osc for example.

It appears that the OP wanted to discipline to line and use that as a long term ref.. It=92s not clear to me how he came up with the =96100 dBc number without an offset =85

I=92m not sure what you mean by =93how big an offset=94 =85 offset generall= y refers to the position of the measurement relative to the carrier. The closer the offset the more difficult the measurement ... generally do to the limitation of the measuring equipment. The interesting part is the solution to those challenges.

I=92m not trying to be a malcontent here =85 just seems like the discussion doesn=92t have direction.

Much faster than Q cycles, I mean. (Posted before breakfast in Albuquerque.)

Cheers

Phil Hobbs

Understood. I agree that the OP's question wasn't that well posed, but there was a bunch of very strongly stated Bad Info here that needed pointing out. I took the OP to be saying "I need a 60 Hz oscillator block that's way, way quieter than I know how to build", and that the rest of us have been making suggestions. Calculating or measuring how good it actually is is his worry.

Cheers

Phil Hobbs

One interesting and often overlooked part is the coaxial ceramic resonator. It's essentially a shorted transmission line formed in a block or tube of hi-K ceramic, usually by silver or copper plating it. They are usually treated by the RF boys as resonators or inductors, but they really act like time-domain transmission lines. TCs are in the single-digit PPMs and Qs in the hundreds or thousands. Dielectric constants are in the hundreds or thousands, so they are very short for their delay/frequency.

Remarkable parts. I use them to make instant-start/instant-stop oscillators in the 600 MHz range. As a VCO, they will have very low phase noise, somewhere between an LC and a quartz crystal.

John

Check out La Posada de Albuquerque. Cool old hotel. Or it was, except they may have "upgraded" it.

John

I don't know about that. It isn't that difficult to calculate a circuit with two caps, an inductor, and an elf who opens and closes a switch at the right moments. It does help to know elementary differential equations.

I haven't actually followed the original discussion closely enough to know who made the first technical error. The larger error IMO is to keep getting into these tiresome p***ing contests, which I decline to do. If what you want is merely to have the correct solution posted, post it and let's move on to some electronics.

Cheers

Phil Hobbs

I confess I'm one of the ones who overlooked them...where do you get them, and do they come in Y5V?

Cheers

Phil Hobbs

I don't think any specific problem has been clearly stated, such that it can be analyzed. My comment, that seems to have ruffled feathers, is that one shouldn't assume as a working tool that charge, coulombs stored in various capacitors in a circuit, is conserved. Sometimes it is, sometimes it isn't, sometimes the concept is silly.

The argument did make me go back and review some basics, which is good. Messing with all this digital and software and opamp stuff can make the old EE101 math get rusty.

John

Don't know. We buy ours from Skyworks/Trans-tech, and they have Er values from 10 to 90. TCs are very good somehow. Lots of people make these things and the little, high-frequency ones are cheap in quantity.

John

Yes! I've enjoyed the discussion. Say could someone explain the the

Is that right?

George H.

The usual oscillator phase noise spec would be " -100 dBc/Hz " at some offset frequency from the carrier. It's often given as a curve. It is possible to convert the curve to an RMS jitter spec... I have a program around somewhere that some s.e.d. guy posted.

John

Dodge, dodge, dodge. You specifically stated, in...

Message-ID:

"... charge is not conserved."

Where, oh great pretend guru, where does the excess charge come from? ...Jim Thompson

This actually kind of makes my point, which I didn't state clearly: if you _don't_ use a divider it'll be hard. With a divider it gets easy, as long as you ignore clock jitter in the divider (and clock jitter probably isn't a big deal, given the output frequency).

Depending on how close to the carrier you want to get, you lose a factor of up to infinity (if you get _really_ close to the carrier).

The noise gain is something like 1/(s^2 + w0^2) -- it's an oscillator. Worse, because it's an RC, the constant you're multiplying by is greater than one -- I get Hn(s) ~ 15/(s^2 + w0^2). That's not taking the current noise of the part into account (which, I admit, I haven't checked on because I'm lazy).

I've been "using" them... designing them into GPS LO's since before you were born ;-) ...Jim Thompson

"Jim Thompson" wrote in message news: snipped-for-privacy@4ax.com...

What's the advantage -- for you -- over crystals? Just lower cost?

---Joel