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Yeah, I suspected you were talking about white noise.

Unfortunately for folks that design low noise freq synthesizers white noise isn=92t the tough spot. We typically live in those 1/f places. The whole process is about shaping that noise profile. Without targeted system spec=92s, one can see why it=92s virtually impossible to select loop components such as a VCO=92s, amps, etc., for this type of job.

Btw, I apologize for the ignorant comment =85 didn=92t mean to sound so nasty. I regret that.

In remote areas, the electricity distribution network is often like a tree (not a ring) and becomes weaker when approaching the leaves of the tree. Connecting one or more 1-3 MW wind turbines at the edges will cause problems.

Ideally, it is assumed that the turbine should provide power to the customers at the local branch. However, when operated close to the cut-in wind speed, the power output will vary significantly, causing voltage variations and the lights will flicker at nearby customers in the weak net.

With wind turbines at different branches of a weak net, some operated below average, some above average power, power is routed long distances along weak lines through the common distribution point of the original distribution net. The direction of power transfer in the weak lines varies constantly, depending on the local wind variations. In effect, the wind turbines in different branches have a slightly different phase compared to each other and the main power grid.

When connecting individual PV or other small scale power sources to a weak net, the control loops must be able to follow much faster phase variations in weak nets with local generation, compared to a strong network.

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I understand your post NOT. Please explain more thoroughly, or point me to texts. I still do not understand the way you are using units for phase modulation. I have trouble understanding phase modulating a 60 Hz carrier with a 1 MHz signal. What is the p-p angle you are achieving? How do you know?

Sorry about sounding like a fool, but i cannot find common frame for us to understand each other.

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Larkin only wishes he were that young. No matter, he posts just like such a brash young punk.

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If that is the case, a simple twist on the standard PFC circuit will do it. Though that may not meet all of the safety requirements, which are rather difficult.

Of course I'd like to be young. Wouldn't you?

As far as behaving like a "brash young punk", I plead guilty, with pleasure. I hope to keep designing better and faster, and skiing steeper and faster, for a good long time. Electronics is not something you have to give up designing after the age of 30.

I knew people who gave up electronics when transistors replaced tubes, and people who refused to learn how to use programmable logic or microprocessors or whatever. May as well move into a managed-care facility and take up miniature golf.

John

If you read the derivation in Section 13.6 and do the math, which isn't difficult--just sums and differences of trig functions--we should be talking the same language.

The main point is that we discuss small-amplitude phase noise using the small angle approximation, i.e. sin theta ~= theta, so that it's just like amplitude noise except that it's in phase quadrature with the carrier. That makes it a bog-standard propagation-of-errors calculation: you take all the noise sources, multiply them by the relevant partial derivatives, and compute the RMS sum.

If you add white noise, half winds up in the I phase, which looks like amplitude variations, and half in the Q phase, which looks like phase variations. The small angle behaviour makes the statistics and frequency spectrum of the resulting phase and amplitude noise equal to those of the original additive noise. It's quite pretty.

When the SNR is below about 20 dB, we have to start being a lot more careful mathematically.

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

Understood. My first engineering job was designing 2/3 of the time and frequency reference boards for the first direct-broadcast satellite system (the Spacetel system from AEL Microtel), including the VHF synthesizer that controlled the 14 GHz local oscillator on both the central station and the remotes. The noise spec was 7 Hz RMS in 5-100 Hz bandwidth around a 14 GHz carrier, i.e. after being multiplied up by

120 times from the output of my board. I was allocated half of this budget, i.e. 5 Hz RMS at 14 GHz, or 0.041 Hz at 115 MHz, and my synthesizer had to be tunable over about 5 MHz in steps of 8.3333... kHz (1 MHz at the LO frequency). This was in 1981-83, remember, which was well before DDS.

I had no idea how hard that was before I started--I had a brand new astronomy and physics B.Sc., and only a hobby background in electronics (though I did start when I was 10 years old). I knew about PLLs, but I'd never seen one, let alone designed one. Talk about being chucked in the deep end of the pool! (I eventually made a fairly novel fractional-N synthesizer with an 833.33... kHz comparison frequency, using a MC12013 ECL 10/11 dual modulus prescaler(*) with the modulus controlled by a 74LS163 synchronous decade counter, whose carry input was driven by a string of CD4527 CMOS BCD rate multipliers. The rate multiplier jitter was pretty well outside the LO PLL's bandwidth, and certainly wasn't in the 5-100 Hz band that they mostly cared about. One nice feature was that you didn't need a switch setting table--because it was BCD and used a synchronous divide-by-12 to get the reference, you just set the BCD DIP switches to the desired 14 GHz LO frequency.

It all eventually worked fine, thanks to Floyd Gardner's book and the Mini-Circuits catalogue. Its main wart was that even with lead-lag compensation, I _still_ couldn't get enough loop gain to control the noise of an LC VCO with a 5 MHz tuning range. I eventually had to retreat and use a VCXO, meaning that you had to change a crystal as well as set the DIP switches. (Changing crystals was SOP in those days, so nobody minded too much.) The oscillator was a one-transistor Colpitts with self-limiting, just like in the ARRL Handbook. If I'd known how to design better oscillators, or had had coaxial resonators, I could probably have kept real tunability. Such is life.

No worries. The plus side of having large areas of ignorance is the opportunity to learn lots of new things, which is one reason I like SED in spite of the spam, troll baiting, and flame wars. I think that standing at a white board arguing about technical stuff with a few smart people is the most fun you can have standing up. (I have a directory full of pithy Usenet posts that I refer to periodically--some of the stuff in my book came out of things I learned here.)

Cheers

Phil Hobbs

(*) Did you design that one, Jim?

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

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Hi Joseph, I'm trying to get my head around this too. (I like Phil's intro to section 13.6, "We live in a fallen world, so the signals we process are never free of noise, distortion, and extraneous interfering signals.")*

I think it would help me if I understood how one measures the phase noise. My simple minded approach would be to trigger my digital 'scope on the carrier zero crossing, and then look 'down stream' 100 or 1,000 periods later and see how much 'jitter' there was in the delayed zero crossing. Seems like there must be a better way.

George H.

*Does this mean there is no noise in heaven? (all R's have zero temperature)

If you don't mind my asking, Phil, how long did that all take?

With the synthesizers-in-a-chip (PLL+VCO), off-the-shelf VCOs, plus the design tools from Analog Devices, etc., I have a suspicion that many such RF generators are now given all of perhaps a day or two of design time. :-)

---Joel

I joined Microtel in about June of 1981, and left in August 1983 to get married and go to grad school. The first few months were working on the system demo, and the rest of it was spent getting the Pilot Tone Generator and Timing & Frequency Unit designed, breadboarded (no SPICE either), laid out, and tested with the 14 GHz LO setup. Plus miscellaneous other stuff.

So I'd say a year, give or take. I had a fair few false starts in there, too, of course--such as trying to use anything with an 8 kHz comparison frequency!

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

quoted text -

One approach is to phase lock a quiet oscillator to the unknown one, with a very narrow loop bandwidth, and look at the noise at the phase detector output.

In _The Screwtape Letters_, C. S. Lewis quotes George Macdonald on the subject of Heaven: "...the regions where there is only life, and therefore all that is not music is silence". (Unspoken Sermons, Vol 1)

So, no noise there. ;)

Cheers

Phil Hobbs

--
Dr Philip C D Hobbs
Principal
ElectroOptical Innovations
55 Orchard Rd
Briarcliff Manor NY 10510
845-480-2058
hobbs at electrooptical dot net
http://electrooptical.net

quoted text -

That's pretty much what the Allan Variance does,

which is to characterize the jitter as a function of the time, or equivalently the number of skipped edges, between the edges you measure. Cheap crystal oscillators may have a few ps RMS between adjacent clock edges (aka cycle-to-cycle jitter) but may have many nanoseconds of jitter if you measure edges that are a second apart.

You've got to be careful about the scope jitter, too. It may well be worse then the oscillator you're trying to measure.

The "real" way to measure phase noise in the frequency domain is to get two of the things you want to test, set them to slightly different frequencies, and mix their outputs, then analyse the mixer output. That's about the only way to characterize really quiet sources. Of course you have to make sure they aren't injection locking or showing the same line-hum jitter or any other sneaky correlation.

We have a couple of 10 MHz atomic clocks around here, one rubidium and one cesium. If you trigger a scope from one and look at the rising edge of the other, you could swear that the scope is triggered internally. At, say, 5 ns/div, it looks rock steady. Come back a half hour later and the trace has drifted a little left or right.

That test is the time-domain equivalent of the mixer thing. That's how we test the timing system stuff we did for NIF: trigger a scope from one unit, observe the rising edge of another.

John

All the Real terms are zero... heaven is purely Imaginary!

Best regards,

Bob Masta DAQARTA v5.10 Data AcQuisition And Real-Time Analysis

Scope, Spectrum, Spectrogram, Sound Level Meter Frequency Counter, FREE Signal Generator Pitch Track, Pitch-to-MIDI DaqMusic - FREE MUSIC, Forever! (Some assembly required) Science (and fun!) with your sound card!

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OK that sounds easy enough... you then have to add a third oscillator and measure each againts the other if you want to really know any individual bandwidth.

Fun! I did the same trick when comparing digital function generators. This cheap protek one had a 'hick up' every second or so and the transistion would slowly march across the screen.

Thanks again John and Phil.

George H.

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Usually just dumping the mixer output into a spectrum analyzer is good enough. One assumes the units are identical. You can use three or more DUTs, in pairs, to demonstrate that.

One of my Tek scopes has a few ps of time shift that correlates to a blinking led on the sampling head.

John