[time-nuts] sub harmonic VCO locking

[Attila Kinali]

On Thu, 30 Jul 2020 21:56:42 +1000
glen english LIST <glenlist at cortexrf.com.au> wrote:

> - a double-double-double could work, but my experience is for x2 x2 x2 I 
> really need to filter well at each stage to avoid sum and difference 
> products.. which might be OK for this application , especially if I 
> filter really well after the first x2 . but avoid if I can. filters at 
> 908 MHz need space, and shield cans where it is going.

Frequency multiplying would be probably the easiest to get low noise,
followed by a well designed PLL system. Though -115dBc spurs is tough,

 
> - and I dont know too much about phase noise and SRD or varactor 
> multipliers. but maybe that's an option.

SDR are prety low noise. From NLTLs we know that varactor systems can
exhibit increased flicker noise levels (probably due to bias point
instability).

 
> - onboard VCO chip/PLLs have all sorts of unrelated spurs in the output.
> 
> - sure I can use a good PLL and a external VCO, but if my N value is 
> fixed, and I can use injection locking, why bother with the PLL chip 
> that is likely to introduce PD related spurs anyway.

The generic way in this case is to build a PLL using frequency multiplier
for the reference and a narrow loop filter after the phase detector.
Placing zeros at the multiples of the (unmultiplied) reference frequency
in the loop filter will reduce the spurs quite considerably.


Injection locking is finicky. To injection lock, the resonator has to be
pretty much on frequency to begin with, and kept that way. But unlike with
other systems, you have no feedback system where get information how far
off you are to control the frequency. Unless you build a hybrid system
of an oscialltor with a Pound lock[5,6] (e.g. like cryogenic sapphire oscillators use[7]) 
You want to read Adler's paper[1] at the very least before you start. 
A look at the work byHuntoon/Weiss[2] and Kurokawa[3,4] is probably also beneficial.


			Attila Kinali

[1] "A Study of Locking Phenomena in oscillators", by Robert Adler, 1946 (reprinted 1973)

[2] "Synchornization of Ocillators", By Huntoon and Weiss, 1947

[3] "Injection Locking of Microwave Solid-State Oscillators", by Kurokawa, 1973

[4] "Noise in Synchronized Oscillators", by Kurokawa, 1968

[5] "Electronic Frequency Stabilization of Microwave Oscillators", by Pound, 1946
http://dx.doi.org/10.1063/1.1770414

[6] "Frequency-Stabilized Oscillator  Unit Notes and Instructions", by Lawrance, 1946
https://dspace.mit.edu/bitstream/handle/1721.1/5024/1/RLE-TR-022-14254857.pdf

[7] "An Ultra-Low Noise Microwave Oscillator Based on a High-Q Liquid Nitrogen Cooled
Sapphire Resonator", by Woode, Tobar, Ivanov, 1995


-- 
Science is made up of so many things that appear obvious 
after they are explained. -- Pardot Kynes